Author Topic: Repairing the IBM Model M2  (Read 56269 times)

0 Members and 2 Guests are viewing this topic.

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« on: Tue, 06 January 2009, 14:51:06 »
The M2 has a bad reputation for not working. Clickykeyboards claims that 4 out of 5 M2s are broken. Bluemercury and xsphat had broken M2s too.

There were theories that PS/2 might use different signal levels than PS/1. I bought mine together with the original PS/1 computer so I thought it would be a working version. I threw that PS/1 away lately as it didn't come with the monitor which contains the power supply. As I couldn't use the 'board on a PS/1 as originally intended I decided it didn't matter anymore. I cleaned it and connected it to my Linux machine. Two LEDs came on immediately:



Otherwise it would do nothing. No characters, no LED switching. Another broken M2.

Here's the tag (german layout):



As I had cleaned it before I tried it, I had seen two SMD electrolytic capacitors on the controller pcb:



These can dry up over time and stop working. After 18  years it is quite possible that they're dry. The solution is to replace them. The small one is 2.2uF 50v, the big one is 47uF 16v. I used these for replacement:

2.2uF 63v electrolytic
47uF 16v tantal

Tantal is better because it doesn't dry but I only had a 2.2uF 35v tantal and didn't want to do it twice if that wouldn't work.

I didn't remove the pcb from the case.

The SMD capacitors are difficult to desolder. I use a very hot temperature, add a little solder for better heat distribution and push the legs to the side. If you push against the capacitor it will finally come loose with a snap and tear the other circuit path off in the process. So pushing the leg to the side seems to be the way to go. Here are the new parts, using correct polarity:



Immediately after soldering in the capacitors I connected the board to the PC. All LEDs stayed off. Tapping on the membrane showed that characters were generated as well!

During re-assembly there will be more holes than buckling springs. So it's good to take a pic before removing the springs:



Finished and working:



Unrelated, removing the numpad will be difficult with this version of the M2. There will be no room for the controller afterwards.
« Last Edit: Fri, 18 June 2010, 06:24:29 by lowpoly »

Miniguru thread at GH // The Apple M0110 Today

Offline itlnstln

  • Posts: 7054
Repairing the IBM Model M2
« Reply #1 on: Tue, 06 January 2009, 15:13:40 »
Sweet.  Congratulations!


Offline Therac-25

  • Posts: 82
Repairing the IBM Model M2
« Reply #2 on: Tue, 06 January 2009, 21:13:44 »
I remember mine fondly.

It died, too :-(
****ty Razer Backlit POS Jesus Don't Ever Buy Razer Christ
Model M Mini
Model M, grey IBM, modular cable.
Model M, blue IBM, modular cable.

Offline iMav

  • geekhack founder
  • Location: Valley City, ND
  • "En casa del herrero, cuchillo de palo"
Repairing the IBM Model M2
« Reply #3 on: Tue, 06 January 2009, 21:53:15 »
I've got two M2's that work just fine.  Refurbished one of them with a full set of new buckling springs.

One great thing about the M2's are the easy accessibility of the BS's.  No frame assembly cracking necessary.  Quite easy to refurbish.

Thanks for the info on the capacitors.  Nice to know if/when mine go out.

Offline xsphat

  • Posts: 2371
  • Location: 'Sconi FTW
  • Enlightened
    • Dan Newman, Writer
Repairing the IBM Model M2
« Reply #4 on: Wed, 07 January 2009, 02:21:07 »
Oh well, I now have the old 1 year old who owns a Model M2, and to be quite frank, he likes the M2 better than I do. Plus, I have a Model M mini sitting right next to me, so I don't need it.

Andn for the record, I had 2 that were broke, but all three lights came on ...

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #5 on: Wed, 07 January 2009, 03:40:16 »
Thanks for the comments.

Quote from: xsphat
Andn for the record, I had 2 that were broke, but all three lights came on ...
Bluemercury had that too (three lights). Might be the same cause or not. We will not know until someone who has that tries the fix.

Miniguru thread at GH // The Apple M0110 Today

Offline Mercen_505

  • Posts: 200
Repairing the IBM Model M2
« Reply #6 on: Tue, 13 January 2009, 08:41:48 »
Oh, nice! I have two M2 boards: a perfectly working IBM from '93, and a non-functional Lexmark from '94. The bad one does just what you described: two LEDs fire, and nothing else happens. I'll have to try this next weekend when I have some spare time.

I *love* how the M2 sounds, as well as the ultra-strong action on the keys. At the same time, the lack of curvature on the board itself tends to mess me up, after years of typing on an M.

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #7 on: Tue, 13 January 2009, 08:56:59 »
Let me know if the fix works for you.

Miniguru thread at GH // The Apple M0110 Today

Offline ozar

  • Posts: 352
Repairing the IBM Model M2
« Reply #8 on: Sat, 28 February 2009, 15:31:47 »
Quote from: lowpoly;17241
The M2 has a bad reputation for not working. Clickykeyboards claims that 4 out of 5 M2s are broken. Bluemercury and xsphat had broken M2s too.

Ouch... my own M2 (1395300) has stopped working, too.

Thanks for posting this because it will come in handy when I get around to opening it up to have a look.

Offline jeffreytk

  • Posts: 2
What do the lights do without reassembly?
« Reply #9 on: Mon, 23 March 2009, 22:18:51 »
I took my broken M2 (Caps Lock and Scroll Lock light and nothing works) and replaced the capacitors but it behaves the same when I plug it in *without being reassembled*.

When the microcontroller is working and the PCB is not installed to the sensing sheets with the key "things" in the right state (all "away" from the sheets???), do the LEDs typically go to all off when plugged into a working keyboard port?

Is there a replacement part for the microcontroller (and its firmware) on this thing? I would easily spend $25-ish dollars on this to make it work since the replacement cost can be much larger than that.

The coolest thing about these old keyboards and Win2000/XP/etc is that you can remap keys.

I made Caps Lock -> Ctrl, Left Ctrl -> Alt (swapped key tops with Left Alt too), Left Alt -> Windows Key, Right Alt -> Mute, `~ -> Esc, Esc -> `~.

Now Escape is where it should be, Ctrl and Alt are where they should be, and I have a Windows Key to do things like WinKey-D to toggle windows, WinKey-E for explorer, not to mention just bringing up the start menu to launch something.

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #10 on: Tue, 24 March 2009, 10:08:42 »
Quote
with the key "things" in the right state (all "away" from the sheets???)
Not sure what you mean by that.

I didn't remove the pcb from the lower case for soldering. After capacitor replacement I plugged the 'board in and the LEDs stayed off (unlike before).

Did you preserve polarity for the capacitors?

Miniguru thread at GH // The Apple M0110 Today

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #11 on: Tue, 24 March 2009, 10:15:24 »
Oh, and welcome to geekhack. :)

Miniguru thread at GH // The Apple M0110 Today

Offline jeffreytk

  • Posts: 2
Capacitor Polarity Checks Out
« Reply #12 on: Tue, 24 March 2009, 13:46:31 »
(thanks for the welcome)

Let me clarify:
With the keyboard disassembled, one cannot know what the state of the capacitive switch is supposed to be. Does key up correspond to the spring+paddle being flat against the membrane, or does key up correspond to the spring+paddle being tilted upward?

I.e., without any spring+paddles installed, will the microcontroller still go into a working state or will it go into some error state ("your keyboard is utterly destroyed, man")?

Since you replace the caps while the PCB was installed, did you test with no spring+paddle parts on the membrane??

I removed my PCB in order to inspect it better and to see if/what components there are on the other side.

My 2.2uF is bipolar. My 47uF is installed right--negative toward silk label.

(If I had a cap tester, I could see if my removed parts were even bad. If they test bad, I either destroyed them desoldering ((small chance)) or they failed in circuit. If they test good, then I can rule out bad caps.)

So--anything else I can do? Any source for the microcontroller?

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #13 on: Tue, 24 March 2009, 14:18:57 »
Quote from: jeffreytk;25270
Let me clarify:
With the keyboard disassembled, one cannot know what the state of the capacitive switch is supposed to be. Does key up correspond to the spring+paddle being flat against the membrane, or does key up correspond to the spring+paddle being tilted upward?
Upward. If no key is pressed no switch is closed. It should work without the membrane connected. The switches are not "capacitive" but buckling spring over membrane. The membrane can be actuated without the buckling spring assembly by pressing the contact area with your finger.

Quote from: jeffreytk;25270
I.e., without any spring+paddles installed, will the microcontroller still go into a working state or will it go into some error state ("your keyboard is utterly destroyed, man")?
It should work.

Quote from: jeffreytk;25270
Since you replace the caps while the PCB was installed, did you test with no spring+paddle parts on the membrane??
Yes.

Quote from: jeffreytk;25270
I removed my PCB in order to inspect it better and to see if/what components there are on the other side.

My 2.2uF is bipolar. My 47uF is installed right--negative toward silk label.
Maybe it's the 2.2uF. Try a tantal or electrolyte one. I did this repair with little electronics knowledge though, so maybe it doesn't matter. However, polarized capacitors won't work if loaded from the wrong side. What if the circuitry depends on that?

Quote from: jeffreytk;25270
So--anything else I can do? Any source for the microcontroller?
I don't think this is an option.

Miniguru thread at GH // The Apple M0110 Today

Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #14 on: Sat, 18 April 2009, 17:37:02 »
Currently going through the keyboard pics thread, where I found this mentioned. Yeah, those pesky early surface mount electrolytics. Good for all kinds of fun in all kinds of devices - DATs, CD players, shortwave portables (Sony in particular), video cameras, whatever.

As for what to do if a swap doesn't work, hmm. The new caps shouldn't be all that much larger than the old ones I imagine (parasitic inductance and all), and it probably doesn't hurt to use tantalums for both (careful soldering them though, they're not that fond of heat). It may be helpful to clean away residue from leaked electrolyte (isopropyl alcohol, sometimes also mixed with H2O dest, should do the trick), as this tends to be conductive and may even cause corrosion. Also check for lifted traces or similar fun stuff.
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #15 on: Sun, 19 April 2009, 12:24:02 »
Quote from: keyb_gr;86354
shortwave portables (Sony in particular), video cameras, whatever.

That's where I learned about the issue, Sony ICF-SW1.

Miniguru thread at GH // The Apple M0110 Today

Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #16 on: Sun, 19 April 2009, 13:55:53 »
Quote from: lowpoly;86419
That's where I learned about the issue, Sony ICF-SW1.

For me it was the ICF-SW7600. Apart from the dead-o-lytics[tm] (and the annoying lack of the external antenna jack in the German version), I actually rather like this model. Mine was entirely recapped fairly recently, and I hope to get the antenna jack issue sorted eventually.
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #17 on: Sun, 19 April 2009, 14:37:50 »
Nice. Here is mine (well, not actually mine):

http://www.dr-boesch.ch/radio/sony-icf-sw1-test1.htm (site in german)

Looks like it uses the same keys/buttons.

Miniguru thread at GH // The Apple M0110 Today

Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #18 on: Sun, 19 April 2009, 15:17:19 »
Quote from: lowpoly;86437
Looks like it uses the same keys/buttons.

Yeah, same NEC microprocessor / PLL IC in there. After I had a look at the datasheet I knew where the (somewhat strange) frequency entering concept came from...

And before it gets off-topic too far, these sets actually have pretty good key feel, tactile with short throw. Older sets (e.g. 7600D, 2001D) still had rubber mat over microswitches, soft but not that bad either. That said, I can't complain about key action on DE1102 and E100 either, only size is an issue with the E100. The Chinese don't always get it right though, the RP2000 (Roadstar TRA-2350P) suffers from slow key scanning.
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline Rajagra

  • Posts: 1931
Repairing the IBM Model M2
« Reply #19 on: Sat, 27 June 2009, 09:57:12 »
I should be getting an M2 soon (or maybe not, the seller underestimated postage and has to sort it out.)

I was thinking of buying some replacement capacitors in advance. I have a couple of questions:

If the old caps have failed, do they go open circuit / low capacitance? If so you could just solder the new ones in in parallel.

Is it obvious from the board which way round to connect the caps? Or do you have to take notes from the existing caps before you remove them?

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #20 on: Sat, 27 June 2009, 16:00:08 »
The + symbol is on the pcb:


Miniguru thread at GH // The Apple M0110 Today

Offline Rajagra

  • Posts: 1931
Repairing the IBM Model M2
« Reply #21 on: Sat, 27 June 2009, 16:09:23 »
Ah, thanks I see them now! :embarassed:

Offline timw4mail

  • Posts: 1307
    • https://timshomepage.net
Repairing the IBM Model M2
« Reply #22 on: Sat, 27 June 2009, 21:06:26 »
Quote from: ripster;99684
Ah, the good old original Model M.  My electrolytics know they can be easily replaced so they BETTER not act up.

Show Image


My controller has two of these commonly available guys.  Still surprised how long they last.


After that era of exploding computer caps...the only capacitors I'm comfortable with are the solid ones.
Pointing devices- CH Products DT255 (With Lapis Lazuli ball), Razer Salmosa, Logitech MX400
Buckling Springs - IBM Model M 1391401 (1987) & IBM Model F AT
Cherry MX Blue Switches - iOne Scorpius M10 "otaku"(2009) & OCN-branded Ducky keyboard
Cherry MX Brown Switches - Compaq MX11800 & Cherry G80-8963LUBUS-2 (MX8100) & Filco FKBN91M/JB (Japanese Tenkeyless)

Cherry MX Black Switches -  US Micro Products Metal Keyboard USMP-KX065-TB-USB-A
Fake Cherry MX White Switches - Qtronix Scorpius 32 keypad &  Chicony KB-5191
White round SMK Switches - Gold VTech label keyboard
SMK blue Monterrey Switches - Chicony KB-5181
Damped tactile ALPS - Apple AEKII
Blue NEC Switches - NEC APC-H412


Quote from: bigpook;129625
: ) life is like a box of webwit. you never know what you are going to get.



Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #23 on: Sun, 28 June 2009, 19:43:40 »
You might enjoy my page on capacitor nonlinearities and linked literature.

It always pays to be somewhat skeptical with boutique stuff - oil paper caps seem to have quite some dielectric absorption, or so Bob Pease mentions. Huge film caps obviously have a good bit of series inductance as well.

Regular electrolytics with a nice bias voltage across them that are not subjected to high ripple currents or temperatures can easily last 25..30 years. The smaller ones which are more prone to drying out may still do 15..20 years with no major problems, so it's not surprising that our Ms are doing so well. A lot of these early surface mount 'lytics seem to have been junk though (as observed with the M2).

The ExplosiCaps[tm] found in PCs were a result of both faulty electrolytics with wrongly copied electrolyte and wrong derating at excessive ripple currents, i.e. the caps were deliberately run at ripple currents over spec (so one could use fewer of them) but the formulas for life expectancy calculation were off. PC mainboards are manufactured under extreme price pressure, don't forget.
When replacing dead electrolytics, some people have installed small film or ceramic bypass capacitors in parallel in order to keep the high-frequency ripple away from the 'lytics. Even though one may have to consider parallel resonance ('lytic series L || bypass C) when using ultra low ESR 'lytics, this usually seems to work well in practice.

Given that the 'lytics in the regular Ms are axial types mounted a good bit away from the microcontroller, I don't think they need anything fancy.
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline timw4mail

  • Posts: 1307
    • https://timshomepage.net
Repairing the IBM Model M2
« Reply #24 on: Sun, 28 June 2009, 20:50:28 »
Quote from: keyb_gr;99833

The ExplosiCaps[tm] found in PCs were a result of both faulty electrolytics with wrongly copied electrolyte and wrong derating at excessive ripple currents, i.e. the caps were deliberately run at ripple currents over spec (so one could use fewer of them) but the formulas for life expectancy calculation were off. PC mainboards are manufactured under extreme price pressure, don't forget.


Planned obsolescence makes me sick... especially in regards to computer parts... What's wrong with the board working in five years still, when I bought a new computer?

I digress....

Are the aluminum caps susceptible to anything similar to the electrolytic cap CAPastrophe?
Pointing devices- CH Products DT255 (With Lapis Lazuli ball), Razer Salmosa, Logitech MX400
Buckling Springs - IBM Model M 1391401 (1987) & IBM Model F AT
Cherry MX Blue Switches - iOne Scorpius M10 "otaku"(2009) & OCN-branded Ducky keyboard
Cherry MX Brown Switches - Compaq MX11800 & Cherry G80-8963LUBUS-2 (MX8100) & Filco FKBN91M/JB (Japanese Tenkeyless)

Cherry MX Black Switches -  US Micro Products Metal Keyboard USMP-KX065-TB-USB-A
Fake Cherry MX White Switches - Qtronix Scorpius 32 keypad &  Chicony KB-5191
White round SMK Switches - Gold VTech label keyboard
SMK blue Monterrey Switches - Chicony KB-5181
Damped tactile ALPS - Apple AEKII
Blue NEC Switches - NEC APC-H412


Quote from: bigpook;129625
: ) life is like a box of webwit. you never know what you are going to get.



Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #25 on: Mon, 29 June 2009, 08:12:37 »
Quote from: timw4mail;99838
Are the aluminum caps susceptible to anything similar to the electrolytic cap CAPastrophe?
You mean solid electrolytic / specialty polymer? Don't think so, they can't dry out.
Quote from: ripster;99857
Well, that's what's surprising me.  The first Model M's shipped in 1985 (Source: Clickeykeyboards) so we are talking 24 years.

I'm not worrying about it, just surprised.
I would guess that the electrolytics present are bulk capacitance and not chosen very tightly. They could show considerable worsening of capacitance and ESR and you may not notice right away. The board might be some more finicky with long cables and stuff like that, but do you notice that unless you have another one for comparison?
« Last Edit: Mon, 29 June 2009, 08:17:03 by keyb_gr »
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline timw4mail

  • Posts: 1307
    • https://timshomepage.net
Repairing the IBM Model M2
« Reply #26 on: Mon, 29 June 2009, 09:51:21 »
Quote from: ripster;99890

When these guys start to dry out I think we'll start seeing a lot of posts like that one.  Caps don't last forever.


Electrolytic ones don't, anyway. I bet the solid ones last a whole lot longer.
Pointing devices- CH Products DT255 (With Lapis Lazuli ball), Razer Salmosa, Logitech MX400
Buckling Springs - IBM Model M 1391401 (1987) & IBM Model F AT
Cherry MX Blue Switches - iOne Scorpius M10 "otaku"(2009) & OCN-branded Ducky keyboard
Cherry MX Brown Switches - Compaq MX11800 & Cherry G80-8963LUBUS-2 (MX8100) & Filco FKBN91M/JB (Japanese Tenkeyless)

Cherry MX Black Switches -  US Micro Products Metal Keyboard USMP-KX065-TB-USB-A
Fake Cherry MX White Switches - Qtronix Scorpius 32 keypad &  Chicony KB-5191
White round SMK Switches - Gold VTech label keyboard
SMK blue Monterrey Switches - Chicony KB-5181
Damped tactile ALPS - Apple AEKII
Blue NEC Switches - NEC APC-H412


Quote from: bigpook;129625
: ) life is like a box of webwit. you never know what you are going to get.



Offline Rajagra

  • Posts: 1931
Repairing the IBM Model M2
« Reply #27 on: Wed, 01 July 2009, 08:59:57 »
Quote from: timw4mail;99895
Electrolytic ones don't, anyway. I bet the solid ones last a whole lot longer.

Brawndo! It's got electrolytes!

Offline o2dazone

  • Posts: 946
Repairing the IBM Model M2
« Reply #28 on: Wed, 01 July 2009, 09:02:44 »
Would you like some more BIG ASS FRIES

Offline itlnstln

  • Posts: 7054
Repairing the IBM Model M2
« Reply #29 on: Wed, 01 July 2009, 09:04:39 »
Wow, the "Thirst Mutilator."  That's quite a claim.  I could have used that for the disc golf tournament I was in this past weekend.  It was HOT (over 100 deg. F).  I was sick afterwards (headache, nausea).  I drank 3+ gallons of water between the night before and the day of the tournament to get/stay hydrated, but it didn't work.


Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #30 on: Wed, 01 July 2009, 12:11:36 »
Quote from: itlnstln;100449
Wow, the "Thirst Mutilator."  That's quite a claim.  I could have used that for the disc golf tournament I was in this past weekend.  It was HOT (over 100 deg. F).  I was sick afterwards (headache, nausea).  I drank 3+ gallons of water between the night before and the day of the tournament to get/stay hydrated, but it didn't work.
Too much water can also be bad. I read that it happens to Marathon runners sometimes. They drink all the time to avoid dehydration but when running, the body can't remove excess water from the blood very well. So with too much water in the blood they feel nausea etc., go to the first aid tent, get misdiagnosed, get an infusion with more water and that's it. Not saying this happened to you and I'm writing this from memory.

Edit: http://www.nytimes.com/2005/10/20/sports/othersports/20marathon.html

Miniguru thread at GH // The Apple M0110 Today

Offline itlnstln

  • Posts: 7054
Repairing the IBM Model M2
« Reply #31 on: Wed, 01 July 2009, 12:24:11 »
Quote from: lowpoly;100503
Too much water can also be bad. I read that it happens to Marathon runners sometimes. They drink all the time to avoid dehydration but when running, the body can't remove excess water from the blood very well. So with too much water in the blood they feel nausea etc., go to the first aid tent, get misdiagnosed, get an infusion with more water and that's it. Not saying this happened to you and I'm writing this from memory.
 
Edit: http://www.nytimes.com/2005/10/20/sports/othersports/20marathon.html

Hmm.  Maybe that was it.  Perhaps I drank too much water.


Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #32 on: Fri, 03 July 2009, 10:24:28 »
Also remember that drinking a lot of pure water is a good way of getting rid of minerals and stuff. Seems like even tea is better already.
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #33 on: Sun, 19 July 2009, 09:26:14 »
Quote from: webwit;103275
That's strange. One of my broken M2s just came back to life.

All by itself (or with some assistance)? Might be time to look for cable breaks and bad solder joints, some cleaning of the board with alcohol couldn't hurt either.
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #34 on: Mon, 20 July 2009, 16:52:54 »
Quote from: ripster;103175
Did anyone ever confirm this fix works (other than the OP's keyboard)?  JeffreyTK's obviously never did.


He used a bipolar cap instead of a polar one. The question whether this would work was never answered. Unless his still non-functional pcb was the answer.

Still, with my board it could have been a case of disassemble-assemble-works. Not very likely though as I didn't remove the pcb.

Miniguru thread at GH // The Apple M0110 Today

Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #35 on: Tue, 21 July 2009, 03:35:29 »
A bipolar electrolytic should generally do just as well. Not so sure about ESR though.
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline huha

  • Posts: 388
Repairing the IBM Model M2
« Reply #36 on: Mon, 03 August 2009, 20:26:31 »
I repaired my M2 today. Used an electrolytic and a tantalum cap just as the OP did. Maybe two electrolytics would suffice, but I had to buy some electronics anyway, so I went for the tantalum.
The small capacitor is quite nice to desolder. Heat everything up (really cheap and nasty soldering iron here I'm afraid) and gently push it to the side. Done. The large one was a pain and I did manage to remove about 2mm of the trace on the PCB. Not as bad as it sounds, as this was still a contact pad, so no real harm done there. I probably should have heated it up even more.
I also tried letting it sit here and unplugging/replugging it after some time webwit-style, which didn't work.

So now, I can confirm two things:
1) The seller was full of ****
2) It works now, so the modification/repair seems to work. Big thanks!

-huha
Unicomp Endurapro 105 (blank keycaps, BS) // Cherry G80-3000LSCDE-2 (blues, modded to green MX) // Cherry G80-3000LAMDE-0 (blacks, 2x) // Cherry G80-11900LTMDE-0 (blacks, 2x) // Compaq G80-11801 (browns) // Epson Q203A (Fujitsu Peerless) // IBM Model M2 (BS) // Boscom AS400 Terminal Emulator (OEM\'d Unicomp, BS, 2x) // Dell AT102DW (black Alps) // Mechanical Touch (chinese BS) Acer 6312-KW (Acer mechanics on membrane) // Cherry G84-4100 (ML) // Cherry G80-1000HAD (NKRO, blacks)

Offline huha

  • Posts: 388
Repairing the IBM Model M2
« Reply #37 on: Tue, 04 August 2009, 00:07:29 »
Quote from: ripster;106720
Great news!  Glad that worked.  Maybe the other guy just used the wrong cap and they can't be bipolar.

So the seller said it was working?


Yes. Oh, it was quite a long story. I only kept it because they're somewhat hard to find. I still feel slightly ripped off although he did give me back half of what I paid for it. I just opted for that option because communication was painfully slow--waiting a week for a reply to even the easiest questions wasn't exactly trust-inducing either, so I didn't want to go through the hassle of returning the board to him.
I'm just pissed because he said it worked, it didn't and the caps were at fault. That's just nothing that can happen during shipping.

-huha
Unicomp Endurapro 105 (blank keycaps, BS) // Cherry G80-3000LSCDE-2 (blues, modded to green MX) // Cherry G80-3000LAMDE-0 (blacks, 2x) // Cherry G80-11900LTMDE-0 (blacks, 2x) // Compaq G80-11801 (browns) // Epson Q203A (Fujitsu Peerless) // IBM Model M2 (BS) // Boscom AS400 Terminal Emulator (OEM\'d Unicomp, BS, 2x) // Dell AT102DW (black Alps) // Mechanical Touch (chinese BS) Acer 6312-KW (Acer mechanics on membrane) // Cherry G84-4100 (ML) // Cherry G80-1000HAD (NKRO, blacks)

Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #38 on: Tue, 04 August 2009, 02:57:33 »
I once got a tip for desoldering these surface mount electrolytics: Squash them with some pliers or so, then you should be able to remove most of the cap with only the legs being left. These can then be desoldered comfortably.
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #39 on: Tue, 04 August 2009, 06:36:46 »
Quote from: huha;106718
I repaired my M2 today. Used an electrolytic and a tantalum cap just as the OP did. Maybe two electrolytics would suffice, but I had to buy some electronics anyway, so I went for the tantalum.
The small capacitor is quite nice to desolder. Heat everything up (really cheap and nasty soldering iron here I'm afraid) and gently push it to the side. Done. The large one was a pain and I did manage to remove about 2mm of the trace on the PCB. Not as bad as it sounds, as this was still a contact pad, so no real harm done there. I probably should have heated it up even more.
I also tried letting it sit here and unplugging/replugging it after some time webwit-style, which didn't work.

So now, I can confirm two things:
1) The seller was full of ****
2) It works now, so the modification/repair seems to work. Big thanks!

-huha

Good that it worked for you. :smile:

I would have taken two tantalums for mine but went with what I had then. New electrolytics should last too.

Miniguru thread at GH // The Apple M0110 Today

Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #40 on: Tue, 04 August 2009, 07:18:28 »
Quote from: lowpoly;106785
New electrolytics should last too.
I'd prefer some brand-name 105° types to some cheapo 85° Taiwanese caps of doubtful quality then, i.e. better a Panasonic FC than some Jamicon or so.

In general, with at least half-decent electrolytics I wouldn't worry too much about them failing in the next 20 or 25 years.

Some people advise against tantalum beads, citing reliability problems (generally intermittent shorts, not a nice failure mode). Tantalums may not be that fond of rapid voltage changes and moisture either.

BTW, the 2µ2 should be easy to replace with a ceramic X5R surface mount part (better don't use Y5V or even the super crummy Z5U).
« Last Edit: Tue, 04 August 2009, 07:22:03 by keyb_gr »
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline talis

  • Posts: 195
Repairing the IBM Model M2
« Reply #41 on: Tue, 04 August 2009, 16:35:57 »
Quote from: keyb_gr;106795
Some people advise against tantalum beads, citing reliability problems (generally intermittent shorts, not a nice failure mode). Tantalums may not be that fond of rapid voltage changes and moisture either.

Its actually the low ESR* and the ability to more quickly adapt to changes in voltage that make tant. caps so desirable for power supplies.  The thing that tends to kill them is the initial inrush current (going from 0v to their steady state voltage), usually they design in a small ferrite to help limit this current.  Once at steady state they can more quickly react to fluctuations in voltage and produce less noisy voltage rails.  I guess not taking into account the inrush current is a fairly common design mistake.

The moisture thing is a problem with most larger high precision components.  You'll find a lot of chips are shipped with desi-packs to help reduce the moisture they absorb.  During reflow the moisture vaporizes and can cause cracks in the component body (or structure in the case of capacitors).  Once through the reflow process, moisture shouldn't really be a huge issue (unless the components get really hot).


*ESR - Equivalent series resistant.  Think of it as an imaginary resistor in series with the capacitor created by the technology used to make the capacitor.
« Last Edit: Tue, 04 August 2009, 16:39:13 by talis »

Offline Rajagra

  • Posts: 1931
Repairing the IBM Model M2
« Reply #42 on: Fri, 14 August 2009, 14:44:11 »
Quote from: Rajagra;99594
I should be getting an M2 soon (or maybe not, the seller underestimated postage and has to sort it out.)


Mine finally arrived, and it has this problem. Time to buy some caps.

Any hints on disassembly? I assume the 2 "security" bolts have to come out.
« Last Edit: Sat, 15 August 2009, 17:20:26 by Rajagra »

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #43 on: Fri, 14 August 2009, 15:17:58 »
Don't remember these bolts and I don't have access to the 'board right now.

IIRC, there are a few screws but the strength comes from many many clips. You have to remove the keys to see them.
« Last Edit: Fri, 14 August 2009, 15:20:21 by lowpoly »

Miniguru thread at GH // The Apple M0110 Today

Offline huha

  • Posts: 388
Repairing the IBM Model M2
« Reply #44 on: Sat, 15 August 2009, 07:41:02 »
Now that's interesting!

My M2 featured two slotted screws. I guess the guy who sold it to me was an *******, after all.

-huha
Unicomp Endurapro 105 (blank keycaps, BS) // Cherry G80-3000LSCDE-2 (blues, modded to green MX) // Cherry G80-3000LAMDE-0 (blacks, 2x) // Cherry G80-11900LTMDE-0 (blacks, 2x) // Compaq G80-11801 (browns) // Epson Q203A (Fujitsu Peerless) // IBM Model M2 (BS) // Boscom AS400 Terminal Emulator (OEM\'d Unicomp, BS, 2x) // Dell AT102DW (black Alps) // Mechanical Touch (chinese BS) Acer 6312-KW (Acer mechanics on membrane) // Cherry G84-4100 (ML) // Cherry G80-1000HAD (NKRO, blacks)

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #45 on: Sat, 15 August 2009, 08:21:33 »
Mine have the common Phillips cross slot.

Miniguru thread at GH // The Apple M0110 Today

Offline Rajagra

  • Posts: 1931
Repairing the IBM Model M2
« Reply #46 on: Sat, 15 August 2009, 17:17:12 »
Ugh, that wasn't fun. The SMT cap took forever to remove. I couldn't find my solder sucker, and braid doesn't seem to work well with the new lead-free solder.

I eventually replaced the dodgy looking 2.2 µF 50V electrolytic with a 2.2 µF 35V tantalum bead (all the shop had.)

Before:


After first assembly, noticed the Esc key foot was out of position. Managed to put that right by prying the case open just a bit.

Fully assembled again, then found some keys didn't work. (Space, B, N, Left, Down, Right, Numeric -).

Stripped it down and tried to remove the PCB to clean the membrane edge conectors. Couldn't do it, too many clips hold it down, and pushing back 2 clips at a time allowed zero movement of the PCB.

Resorted to wiggling the membrane around. It moved freely, and I think this wiping action cleaned the contacts.

Assembled again, and so far it works!

My advice is:

  • Don't buy a faulty one of these expecting a quick fix.
  • When fixing one, test it in every way you can at every opportunity. Use a PS/2»USB convertor so you can hot-plug it as often as you want.
  • Don't do the labour-intensive steps (inserting the feet or keycaps) until you've done all the tests you can.
  • I did the final key cap installation while running Aqua'S Key Test, so I knew the keys worked as well as clicking properly.

EDIT> The faulty cap did seem to be open circuit. Simply soldering the new cap in parallel might well provide the fix.
« Last Edit: Sat, 15 August 2009, 17:31:04 by Rajagra »

Offline Rajagra

  • Posts: 1931
Repairing the IBM Model M2
« Reply #47 on: Sat, 15 August 2009, 17:46:04 »
Quote from: ripster;109945
Did you try the crushing/removing the cap trick?

Soldering looks fine to me - I'm doing some Blue Cube connector mods and the desoldering part is by far the hardest.  On through hole that last bit of solder just doesn't want to come out.


No, I thought crushing might rip the tracks up.

It looked like the small cap had leaked to me. I couldn't get any response from it using a resistance meter (I reversed the probes, and hence voltage, but there was still no flicker of current.)

The square stabilising base under the SMT cap appears to be the cause of difficult removal.

Offline JBert

  • Posts: 765
Repairing the IBM Model M2
« Reply #48 on: Sat, 15 August 2009, 17:58:13 »
Quote from: ripster;109945
Soldering looks fine to me - I'm doing some Blue Cube connector mods and the desoldering part is by far the hardest.  On through hole that last bit of solder just doesn't want to come out.
I'm by no means an expert, but in such cases I sometimes drop a litte bit of recycled solder onto the lead so I can put my desolder pump into a larger pool of solder. This also helps to transfer the heat of your solder iron to the lead whereas it can be hard to melt that last bit of solder.

Of course, this may not work if the PCB is not a mere one-sided one. In such cases, the copper in the hole goes from the back- to the front-side and may attract the last bits of solder.
IBM Model F XT + Soarer's USB Converter || Cherry G80-3000/Clears

The storage list:
IBM Model F AT || Cherry G80-3000/Blues || Compaq MX11800 (Cherry brown, bizarre layout) || IBM KB-8923 (model M-style RD) || G81-3010 Hxx || BTC 5100C || G81-3000 Sxx || Atari keyboard (?)


Currently ignored by: nobody?

Disclaimer: we don\'t help you save money on [strike]keyboards[/strike] hardware, rather we make you feel less bad about your expense.
[/SIZE]

Offline talis

  • Posts: 195
Repairing the IBM Model M2
« Reply #49 on: Mon, 17 August 2009, 12:00:12 »
If its RoHS the issue tends to be getting the solder all the way through up to a temperature hot enough to melt it (and hot enough that it doesn't drop below the melting point the second you take the iron away).  The other issue that tends to come up more often is a small amount of solder keeps the pin connected to the through hole plating.  This is most dangerous as it tends to result in the plating being pulled out with the pin.

If you can be destructive in your through hole desoldering, its usually best to just plan to suck up the remainder of the pin into the solder sucker (unless its a vacuum type one that tend to plug easily).

SMT electrolytic aren't bad if solder wick works well for you :

Start by adding a bit more solder to one side.


Then use the wick to remove as much solder as you can from both pads :


Apply heat to one side while gently rocking the cap away from the pad.  This will lift one contact (you don't need to go far, since most of the solder was removed by the wick).


Then heat the other side and remove the cap.  It doesn't take much to remove them with this method, and its very unlikely that you'll pull up a pad or damage the board.  After you're done, clean up the pads with a bit of solder wick.
« Last Edit: Mon, 17 August 2009, 12:07:08 by talis »

Offline rdh

  • Posts: 121
Repairing the IBM Model M2
« Reply #50 on: Mon, 17 August 2009, 12:54:44 »
Quote from: ripster;110213
oooo..... nice instructions for SMT removal.  Looking forward to your soldering tutorial as well.

[STRIKE]The tutorial seems to be under construction in the wiki.[/STRIKE]

EDIT: Nope, never happened.  Pay no attention to the man behind the curtain.
« Last Edit: Mon, 17 August 2009, 14:19:55 by rdh »
at home: IBM "Space Saving" Model M
at work: Topre Realforce 87UKB55


Offline talis

  • Posts: 195
Repairing the IBM Model M2
« Reply #51 on: Mon, 17 August 2009, 13:57:13 »
Quote from: rdh;110217
The tutorial seems to be under construction in the wiki.


Shhhh, don't tell anyone yet.

Offline Mercen_505

  • Posts: 200
Repairing the IBM Model M2
« Reply #52 on: Mon, 17 August 2009, 15:30:52 »
*sigh*

I've still got a pair of dead M2s I need to repair one day. I've soldered things like db9 connectors and such, but I've never messed with anything already mounted to a board. Gotta take the plunge eventually!

Offline Rajagra

  • Posts: 1931
Repairing the IBM Model M2
« Reply #53 on: Mon, 17 August 2009, 16:10:56 »
The reason I had a tough time with the desolder braid was probably because of my old, low power (25W) soldering iron, I don't think it's enough for the new eco-friendly solder. (Ironic, if you think about it!)

I'm still convinced I could have just connected the new cap in parallel with the old one. I should have been more methodical and clipped it in place to test it.

Offline Qwertyuiop

  • Posts: 32
Repairing the IBM Model M2
« Reply #54 on: Sun, 06 September 2009, 02:39:52 »
After learning about this bad capacitor issue with the M2, I borrowed a pair of them that do not work. I believe they originated here:
http://www.clickykeyboards.com/index.cfm/fa/items.main/parentcat/9245/subcatid/0/id/332692

I knew they didn't work but I did not check their exact behavior before attempting repair. I disassembled them and the solder joints on both of the capacitors on both boards were corroded black. I have access to a vacuum-powered desoldering tool but due to the corrosion it was still a pain to remove the caps.

But I did get them off and replaced them. Unfortunately they are still unusable. Connected to a PC, upon boot the LEDs flash the way they're supposed to, and Caps Lock/Num Lock/Scroll Lock turn the appropriate LEDs on and off. F2 will successfully get me into the BIOS (Intel motherboard). Once there, I can navigate using the numpad arrows, but the dedicated arrow cluster does not work, nor does it appear that the six keys above do. Other keys I can check in BIOS work, like Y/N. I can't do much beyond that since CTRL-ALT-DEL doesn't work which means I can't log onto Windows (Win 2000 on this machine).

While it could be something else like the contact between the controller and the membrane, that doesn't seem likely since both keyboards behave in this exact same manner.

I suspect this is beyond my ability to fix but I thought I'd post the info for reference.
several Model M\'s, Apple Adjustable Keyboard

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #55 on: Sun, 06 September 2009, 05:44:06 »
Must be something different.

Too bad the "before" state is unknown. Can you ask the person you got the 'boards from?

Miniguru thread at GH // The Apple M0110 Today

Offline Qwertyuiop

  • Posts: 32
Repairing the IBM Model M2
« Reply #56 on: Sun, 06 September 2009, 09:49:20 »
I did already but he's not sure either. He knows the LEDs did something but doesn't remember if they behaved like other keyboards. He primarily uses Model M spacesavers so he's not used to LEDs at all. Whatever he tried to test he thought the Esc key worked so it may be that my repair did nothing at all and the caps were ok even though the contacts were corroded.

It occurred to me that perhaps these are some odd variant of the keyboard and the keys that don't appear to work actually do but send non-standard scan codes.
several Model M\'s, Apple Adjustable Keyboard

Offline quadibloc

  • Posts: 745
  • Location: Edmonton, Alberta, Canada
  • Layout Fanatic
    • John Savard's Home Page
Repairing the IBM Model M2
« Reply #57 on: Sun, 06 September 2009, 11:12:39 »
I remembered reading somewhere that all the M2s were rubber dome, so when I picked up two with buckling springs at a thrift shop, neither of which worked, I assumed that they were for a terminal. This article inspires me to try and fix mine, by carefully replacing the capacitors, and thus have a couple of additional Model Ms... which will also save a bit of space on the desk!

Offline Rajagra

  • Posts: 1931
Repairing the IBM Model M2
« Reply #58 on: Sun, 06 September 2009, 14:06:17 »
Quote from: Qwertyuiop;115218
I can't do much beyond that since CTRL-ALT-DEL doesn't work which means I can't log onto Windows (Win 2000 on this machine).

Plug in a second keyboard to log in, then use Aqua'S Key Test.

If I open up my M2 again I think I will tie/loop dental floss around all the springs before removing the case, will save a lot of time.

Offline Qwertyuiop

  • Posts: 32
Repairing the IBM Model M2
« Reply #59 on: Sun, 06 September 2009, 16:27:58 »
Quote from: ripster;115251
You could always load up Aquakeytest or Autohotkey and look to see if scan codes are generated.

Also, posting a pic of the back label might help.

Next logical step would be to pop it open and look for corroded membranes and coke spills.

I'd have to be able to get into Windows to run those programs though. Rajagra's suggestion for a second keyboard is a good one; I'll see about borrowing a USB keyboard so I can do that since all I have are PS/2 and I don't believe two of those are supported. I think the person with the M2s has some USB Apple keyboards.

For the moment they're back with their owner so I can't check but I assume the label in the Clickykeyboards link I posted is the right one. If I get them back I'll verify but I can't post a pic since I don't have a camera.

Since I replaced the caps they've been open and I didn't see any corrosion aside from on those caps and some more on the IC on the board. I tried to clean the latter off and it appeared to only be surface corrosion. The "before" pic Rajagra posted on the previous page shows the same kind of corrosion on the solder joints of the small cap that were on all the ones on these two boards.
several Model M\'s, Apple Adjustable Keyboard

Offline comp_wiz101

  • Posts: 5
Repairing the IBM Model M2
« Reply #60 on: Sun, 20 December 2009, 01:22:44 »
Hello everyone! I type my first post on the forums on my newly repaired IBM M2 keyboard I picked up from a thrift shop today. Thank you everyone for your excellent photos, as well as the wonderful person that posted the article in the first place. I was having the 2-led problem as well, so on a lark I de-soldered the SMD capacitors (my first experience doing anything to SMD) and with the large pads provided, soldered in the worst melange of capacitors I could find...
The 2.2uf 16V was replaced with a 1.6uf 28V electrolytic, and the 47uf was replaced with a 22uf 200V (!) electrolytic. I suppose the big hope now is that nothing burns out...

I hadn't really expected it to work, or for the parts to fit into the shell, but with a bit of nudging around, and using a common ground lead for both caps I managed to shoehorn the mess back into the casing. (Should have taken a picture of that mess...)
To my surprise, the keyboard is now working flawlessly! I'm very pleased with the nice clickity-clack of the keys, reminds me of the computers I started out on.

So, thanks everybody!

Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #61 on: Sun, 20 December 2009, 11:31:34 »
The old caps probably had close to zero capacitance left and an astronomical ESR, so the new ones still are a whole lot better. It would seem that keyboards aren't particularly picky in terms of electrolytic capacity or position, I'd guess there already are some ceramic supply bypass caps nearby.

Where on earth does one find a 1.6µ 28V though? :? That's a very odd value in both capacitance and voltage rating. Either it was some super special custom job (they're not normally made in E24 values as the tolerances are quite big anyway, commonly +/-20% or even +50%/-20%) or you misread the ratings on a 1.5µ 25V.

Incidentally, while I do not have a schematic for the M2, there is one for a regular M from the Kbdbabel project. This uses two 47µ electrolytics, one for supply buffering (in addition to one 100n and two 1n ceramics) and another one as part of an R-C network for keeping the reset pin low for some time after power is applied. If they increased the resistor value in order to reduce the value of the second one to 2µ2, excessive leakage current might result in reset being held low all the time, so the board would never boot up. Then again, it could also be a simple case of reset going high before power is stable, thus causing the microcontroller to hiccup. Who knows.
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline chozar

  • Posts: 4
Repairing the IBM Model M2
« Reply #62 on: Sun, 13 June 2010, 04:45:44 »
I appreciate the effort the original poster put into detailing this repair.

The photos unfortunately are not showing up for me here.  Does anyone else have this issue?  I would love it if the OP could get them functioning again, that could be very helpful.

Thank you very much.

Offline Rajagra

  • Posts: 1931
Repairing the IBM Model M2
« Reply #63 on: Sun, 13 June 2010, 19:52:18 »
The pictures do seem to have disappeared. Here's a pic I took when I did the fix:



You can see that in my case the top capacitor looked suspicious, and replacing that fixed the problem.

Offline chozar

  • Posts: 4
Repairing the IBM Model M2
« Reply #64 on: Tue, 15 June 2010, 05:08:30 »
Thank you for the response.  I got an M2 that has an rj11 connector that I will be replacing, others have done so before.  But in the process, I wanted to replace the caps.  I'm no EE so I thought the caps were solid, but they look just as they do in your picture.

I'm a little handy with solder, but not a professional.  Anyone have a suggestion as to which digikey replacement I should use?  The selection is huge.  I wanted to get some caps that were solid and would outlast everything, but I just don't know enough.  Digikey has a nice assortment of tantalum caps but I get the impression that they are much larger than the originals, I don't want anything too difficult to install.

Rajagra, where did you get your replacement caps?

Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #65 on: Wed, 16 June 2010, 15:43:40 »
Honestly, I think you'd be fine with regular surface mount electrolytics these days - it's just those early ones that sucked badly. Best go with one of the big cap makers, preferably Japanese (Michicon, Panasonic, whatever), and 105° types can't hurt. You may be able to upgrade to a higher voltage rating and/or capacity along the way (with the same physical dimensions), which can't hurt.

Expect new caps to last about as long as the regular ones of yore, which would be like 20+ years for good-quality parts. Of course, some OS-CONs would last an eternity and a half, but whether that's required is another matter.

The 2µ2 would invite replacement by a ceramic type in any case, you should be able to find one in 0805 or 1210 size.
« Last Edit: Wed, 16 June 2010, 15:51:07 by keyb_gr »
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline Rajagra

  • Posts: 1931
Repairing the IBM Model M2
« Reply #66 on: Wed, 16 June 2010, 19:45:33 »
I got my replacement from Maplin, probably the only common high street shop you can still buy electronic components from here in the UK.

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #67 on: Fri, 18 June 2010, 06:27:56 »
Quote from: chozar;192687
The photos unfortunately are not showing up for me here.


imageshack.us turned out to be a bad choice.

Hosting them on my own server now.

Miniguru thread at GH // The Apple M0110 Today

Offline Hydron

  • Posts: 15
Repairing the IBM Model M2
« Reply #68 on: Fri, 18 June 2010, 20:33:41 »
Quote from: keyb_gr;193742
The 2µ2 would invite replacement by a ceramic type in any case, you should be able to find one in 0805 or 1210 size.


You'll be able to replace them both by ceramic actually - you can get suprisingly high value ones these days. I've just replaced a bunch of tantalums in a product with 47u 16v ceramics, saving money and improving reliability. Note that you cannot use them in some circuits - in some ways they are too close to an ideal capacitor, and make voltage regulators oscillate.

Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #69 on: Sat, 19 June 2010, 11:52:28 »
Quote from: Hydron;194508
Note that you cannot use them in some circuits - in some ways they are too close to an ideal capacitor, and make voltage regulators oscillate.

Yep, their ESR is rather low, and you have to make sure the voltage reg can take that.

BTW, tantalums usually seem to be killed by high inrush currents (provided they survive soldering, which they don't like very much either). Apparently back in the olden days, their data sheets pretty clearly stated not to use them with too low a source impedance, but this was ignored all too often.
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline Hydron

  • Posts: 15
Repairing the IBM Model M2
« Reply #70 on: Mon, 21 June 2010, 07:39:04 »
I'm usually using them after voltage regulators, so inrush isn't normally an issue. Getting a bad batch of caps that blow up a decent portion of the time on first powerup was an issue once though. That was fun during product testing...

Offline fsck

  • Posts: 2
Repairing the IBM Model M2
« Reply #71 on: Tue, 03 August 2010, 23:43:04 »
So my friend and I attempted to repair my M2 this past weekend using the fix mentioned in this thread.

We removed the capacitors by heating them up on their bottoms with a soldering iron and then crushed them with pliers and slowly pulled them out. You'll notice in the picture that we didn't remove the pad for one of them.

We soldered the upper capacitor with its long legs intact to keep it from being near the lower one (I know the soldering job looks bad, but we're not enough of experts to try to solder them with just small legs directly to the board).

Originally, the lower capacitor was soldered to the board with wires, and the keyboard came back to life! However, we then removed the wires and attempted to solder the capacitor directly to the board. While we were able to solder the foot touching the positive (upper) terminal, we tried several times and just could not get the lower foot to stick to the lower terminal. Worse, when we hold the lower foot to the negative terminal and plug in the keyboard, it still gives us the two-lights-on-no-working-keys problem (this happens with or without the leg touching). If the keyboard still doesn't work when we have the capacitor contacting the metal terminal on the board, did we destroy the board?

I have a picture below detailing our "work". I'm hoping someone has some suggestions. I still have 2 more M2s with this same problem... It's weird. I bought this one 8 years ago and have used it without any problems. Then I opened it last summer to clean it, and it got this problem. Around that time, I bought two more M2s off of eBay. One of them came broke but worked after I opened it and cleaned it, and the other one worked for a while. Then after a few days (weeks?) they both started this same behavior! Meanwhile I've been happily typing away on my '90 Model M for over a year...

Anyway, here's the pic -- sorry about the blur! It was the best I could do. Any help would be appreciated! :)



EDIT: Picture is back! It was here for a while and then disappeared.
« Last Edit: Wed, 04 August 2010, 15:59:00 by fsck »

Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #72 on: Wed, 04 August 2010, 10:10:37 »
Blurry pics are bad enough - but this one I can't see at all! ;)

(Sharp photos of small stuff require macro mode and good light. I have taken some almost directly under a desk lamp in the past, which obviously works better with fluorescents.)
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline fsck

  • Posts: 2
Repairing the IBM Model M2
« Reply #73 on: Wed, 04 August 2010, 16:41:42 »
Yeah, sorry about that. It seems good now.

Offline Rajagra

  • Posts: 1931
Repairing the IBM Model M2
« Reply #74 on: Wed, 04 August 2010, 17:49:55 »
The problem could be one of several things. The solder joint may have gone dry so it doesn't conduct well (also explaining why it's hard to solder the leg to it.) The heat may have damaged the capacitor. The capacitor may be fitted the wrong way round (easily done even when you know better.) Damage to the board is possibly the least likely problem, unless you can see part of the track lifted during removal of the old cap.

Offline Tables

  • Posts: 2
Putting it back together
« Reply #75 on: Wed, 03 November 2010, 13:04:26 »
I recovered a Model M2 from the attic (was working perfectly the last time I had tried it a while back), and had to replace the caps because they had dried out. Since the capacitor replacement, every keyboard contact works when I type directly on the contacts while the keyboard is plugged in.

The problem is that I can't put it back together in a _satisfying_ way...

I carefully place the buckling springs in their original position while the top cover is upside down mounted on 2 shims, then I lay the gray rubber mat on top of the buckling springs and make sure all the holes are aligned. I carefully clip the bottom cover (the one holding the control board and capacitors) over everything else and make sure nothing catches in the process (tricky). I flip the keyboard around and start putting the keys back in their slots.

Every time so far (tried about 10-11 times), I find that there's a key that is very sensitive or "sticks" after being depressed. What I mean by that is that for certain keys, I manage to generate keystrokes even before the key is halfway down. I hear the 'clicky' noises for those keys, except that the keystrokes on screen appear before the spring rocks. Sometimes after a reassembly attempt it's the opposite: the same key 'clicks' but generates no keystroke. This always happens on the same 3 keys: 'backspace', '.' (period), and 'left alt', but not always at the same time. My guess is that it's the contacts moving a bit when I clip the kb back together, or the gray mat getting on the way, but I'm not sure. I made sure there was no dirt or anything in the way, and tried shuffling some buckling springs around, but no luck.

Has anyone else experienced a similar problem, or can someone suggest a solution?

Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #76 on: Wed, 03 November 2010, 18:07:38 »
Oops, seems I should have checked on this thread again...
Quote from: fsck;208943
Show Image

Man, that's some seriously long legs on the upper electrolytic there. Ever heard of parasitic inductance?

Anyway, the problem with not getting the lower cap soldered could be due to too weak a soldering iron. If there's a ground plane attached there, it'll suck up the heat. Best use a proper temperature controlled soldering station with like 50 watts max. A measly 16 watt iron is likely to be an exercise in frustration.

Tables, sorry I can't be of any help but I never had an M2 apart.
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline Tables

  • Posts: 2
Putting it back together -- concluded
« Reply #77 on: Thu, 04 November 2010, 16:51:09 »
I finally managed to get it working properly!
I would have thought the soldering part would be the difficult part...

I think it was really the rubber mat and/or the membrane moving around during re-assembly that was causing problems. I paid a lot of attention to what I did. This may seem intuitive to someone who has never had to re-assemble one of these, but after having reassembled this thing a dozen of times and getting different results each time you start thinking it's the little details that count. Could also be that after 10 years of typing (and maybe 8 spent in the closet), these keyboards start to expect components to be replaced _exactly_ the way they were.

This time I reassembled the whole thing with the keyboard oriented such that when I lowered the bottom cover (the one with the membrane and pcb) down on the top cover (with springs in place covered with the rubber mat), the side with the pcb was the furthest away from me (and the row containing the spacebar location closest to me). This made it easier for me to join the bottom cover to the top cover. I used my left thumb to hold the keyboard cable firmly in place on the back side of the cover (it tends to slip from its notch on the casing), and you get to view and align the curvy side of the casing more easily because it's close to you.

While lowering the bottom cover onto the rubber mat (and springs), I pressed the membrane against the bottom for as long as I could fit my fingers between the top and bottom part (in my case, when upside down the membrane tends to slightly lift from the metallic place, slide along the retention clips and become loose in the center of the board).

I repositioned the rubber mat a few times when lowering the bottom cover. Sometimes the retention clips displaced the rubber mat when they weren't perfectly aligned with the holes in the top cover (and mat). If the clips hit or touch (even the slightest touch) any of the locations of the mat covering a hollow section in the casing, it makes a slight crease in the mat. I think that's the step where I should have been more perfectionist before. I moved on to clipping the 2 parts together once I was fully convinced to be perfectly aligned on the first try and hadn't feel the slightest amount of resistance when lowering the bottom cover. If you get it wrong, you put the bottom cover away, reposition the mat over the springs (I only had to reposition springs on a couple occasions, they usually stay in place) and try again.

Then, once the retention clips were fully aligned with the holes and resting (but not yet fully clipped), I pressed uniformly on the board with two hands, to try to get every retention clip to snap in place at the same time. If you snap one side at a time, I think it's possible for the rubber mat to bend or move slightly as the stress goes from one side to the other. My keyboard is from 1992, and the mat seems thinner exactly where the center of the base of the springs from usage over time. If the mat moves around even slightly, I guess this changes the sensitivity of the key.

I just hope I don't have to disassemble this thing for another 15 years -- If the tantalum caps (and my soldering) can withstand aging.

So, keep trying.

Offline AIM-9X

  • Posts: 2
Repairing the IBM Model M2
« Reply #78 on: Thu, 20 January 2011, 20:07:27 »
This is precisely how I repaired mine and it works perfectly.  I had the exact problem of stuck LEDs, and tore everything apart and desoldered both the 47 and the 2.2, and found that the 2.2 had completely dried out (the 47 had not).  I just went to radio shack and got a couple of electrolytic capacitors, a polarized 47uF/32V and a bipolar 2.2uF/50V (I didn't use a tantalum, as recommended, but it worked).  I just made sure the voltage cap was enough, and used the same capacitance ratings.  I would say the solder job was truly the easy part.  Putting it all back together took quite a bit of time and patience.  I had to tape the key switch circuit sheet in place to prevent it from falling out, and I placed the rubber mat as you described.  Placing 101 springs is quite tedious.  I had to remove the stabilizer bars from some of the larger keys, as they seemed to be hindering feedback.

Offline Cern33

  • Posts: 2
Repairing the IBM Model M2
« Reply #79 on: Thu, 23 June 2011, 14:17:48 »
Just picked up a Lexmark 1395300 M2 made in Sept 93 for $0.74 at the thrift store.  It has the usual problem with the LEDs lighting up but not working.  Wish me luck repairing it.  I have very little experience with this sort of thing

Offline Ascaii

  • Posts: 415
  • Location: Berlin, Germany
Repairing the IBM Model M2
« Reply #80 on: Thu, 23 June 2011, 17:22:00 »
if anyone needs an m2 for spare parts/modding project i have a few lying around that ill let go for the cost of shipping plus tip if you feel like it^^.
"Mechanical keyboards are like pokemon:
you start with one, and then you wanna catch em all."

Offline mich

  • Posts: 156
Repairing the IBM Model M2
« Reply #81 on: Fri, 24 June 2011, 04:56:26 »
Hi everyone.

I've recently acquired an M2. It works, but I suspect there is something wrong with the membrane contacts (sometimes a bunch of keys stops working until I squeeze the upper right corner of the case).

Has anybody tried to remove and reinstall the PCB? Is it difficult to realign correctly?

Also, I'm considering preemptively replacing the caps. Are there any possible side effects from using ceramics rated only for 10V?

Offline keyb_gr

  • Posts: 1384
  • Location: Germany
  • Cherrified user
    • My keyboard page (German)
Repairing the IBM Model M2
« Reply #82 on: Fri, 24 June 2011, 07:20:01 »
Quote from: mich;366803
Also, I'm considering preemptively replacing the caps. Are there any possible side effects from using ceramics rated only for 10V?

As long as they're X7R dielectric, they should be fine. I'm not sure this is really needed though - these surface mount 'lytics tend to be dead because they were soldered too hotly and their rubber seals suffered, making them prone to drying out.
Hardware in signatures clutters Google search results. There should be a field in the profile for that (again).

This message was probably typed on a vintage G80-3000 with blues. Double-shots, baby. :D

Offline mich

  • Posts: 156
Repairing the IBM Model M2
« Reply #83 on: Wed, 29 June 2011, 04:44:53 »
OK, so I've finally disassembled the thing and cleaned these contacts. So far the board works fine.

Turns out that mounting the PCB is a piece of cake (everything "just matches"), but removing it required quite a bit of work. There are five latches holding the PCB and I had to open them one by one, lock them opened with thin sheets of plastic and then lift the PCB with a screwdriver.

The only thing I like in this insane design is that you can break one of the latches and the PCB will still sit firmly in place :smile:

edit: I haven't bothered with the caps, they indeed look like being no fun to desolder.
« Last Edit: Wed, 29 June 2011, 04:50:28 by mich »

Offline The Solutor

  • Posts: 2262
Repairing the IBM Model M2
« Reply #84 on: Wed, 29 June 2011, 05:55:08 »
Quote from: mich;366803


Also, I'm considering preemptively replacing the caps. Are there any possible side effects from using ceramics rated only for 10V?


Ceramics are better than electrolitycs, way better. The latter are used just because are cheaper and/or smaller for a given capacity.

10V is the double of the voltage  present on a keyboard, so anything above 5V is fine, 10V is waaay more than enough
The problem with quotes on the Internet is you never know if they are true  (Abraham Lincoln)

Offline Cern33

  • Posts: 2
Repairing the IBM Model M2
« Reply #85 on: Sun, 03 July 2011, 00:09:30 »
Got mine working.  First time I had ever soldered anything and I was pretty sure i had ruined while desoldering the old caps and if not then, while soldering the new ones on.  
Used a 47uF 35v polarized electrolytic and a 1.0uF 35v tantalum.  Best I could get at Radioshack.

Offline jpc

  • Posts: 363
Repairing the IBM Model M2
« Reply #86 on: Tue, 05 July 2011, 20:39:19 »
The fix works! :biggrin:

Removing the old caps is a cinch-- squash them with pliers, they pop right off except the leads and plastic base. The base with pop off, the leads are easily desoldered.

Thanks, OP!

RSI prevention recipe:[/B] Kinesis Contoured, Colemak layout, touch typing, Contour Design Rollermouse,  Logitech TrackMan Wheel, Logitech m570 trackball, "workrave" break timer software, "awesome" window manager, tenkeyless boards, cherry browns, Wang 724 with "ghetto green" ALPS, standing desk and/or comfy adjustable chairs, stress reduction, computer time reduction.

Fun non-ergonomic things: bolt modded Model M Space Saving Keyboards with new springs, Kensington Expert Mouse v7, Unicomp Endurapro, Northgates

Offline Touch_It

  • Posts: 700
Repairing the IBM Model M2
« Reply #87 on: Thu, 07 July 2011, 02:14:49 »
could bad capacitors cause t, y,[,] and backspace keys not to work.


having that issue, though im thinking it probably has more to do with a bad trace


Visit the Typing Test and try!

Offline jpc

  • Posts: 363
Repairing the IBM Model M2
« Reply #88 on: Thu, 07 July 2011, 18:59:02 »
A word to the wise: remove the controller from the case before soldering. I soldered mine in place, and warped the membranes from the heat. Removing the controller is not that difficult.

It seems like the M2 is more fragile than the Model M.

This M2 had a bad trace, I'm repairing it with a trace pen. Never had to do that on about a dozen Model Ms.

I've bent two springs on the M2 while inserting or removing keys. Never had that problem with the Model M either.

It'll be a nice board if it ever works.

RSI prevention recipe:[/B] Kinesis Contoured, Colemak layout, touch typing, Contour Design Rollermouse,  Logitech TrackMan Wheel, Logitech m570 trackball, "workrave" break timer software, "awesome" window manager, tenkeyless boards, cherry browns, Wang 724 with "ghetto green" ALPS, standing desk and/or comfy adjustable chairs, stress reduction, computer time reduction.

Fun non-ergonomic things: bolt modded Model M Space Saving Keyboards with new springs, Kensington Expert Mouse v7, Unicomp Endurapro, Northgates

Offline mich

  • Posts: 156
Repairing the IBM Model M2
« Reply #89 on: Sat, 09 July 2011, 02:53:21 »
I knew I'll have to disassemble this board again. My M2 was laying disconnected for few days and yesterday it greeted me with the Green Leds Of Death. I've replaced these electrolytics with 47/2.2 μF SMD ceramics and it seems to work.


Quote from: jpc;375716
A word to the wise: remove the controller from the case before soldering. I soldered mine in place, and warped the membranes from the heat. Removing the controller is not that difficult.

Yeah, the PCB is laying directly on the membranes.

Quote from: jpc;375716
I've bent two springs on the M2 while inserting or removing keys. Never had that problem with the Model M either.

You have to make the spring stand straight and insert the key exactly vertically, otherwise the spring will bend and get smashed between the spring compartment and the key. It's less of a problem on the M because it's spring compartments are higher. Anyway, I've completely disassembled my M2 three or four times and never bent a single spring so it can be done if you are careful.

Quote from: jpc;375716
It'll be a nice board if it ever works.

I'm not really sure about this "nice" thing, it's awfully loud and definitely feels less solid than the M. And it's a ***** to disassemble.

BTW, I've took a photo of the membranes. Clearly t,y,[,],backspace share a common trace.
« Last Edit: Sat, 09 July 2011, 03:31:58 by mich »

Offline The Solutor

  • Posts: 2262
Repairing the IBM Model M2
« Reply #90 on: Sat, 09 July 2011, 08:22:53 »
Quote from: mich;376771


I'm not really sure about this "nice" thing, it's awfully loud and definitely feels less solid than the M. And it's a ***** to disassemble.

 
I can't agree, the keyboard looks more like a nice Olivetti clone than a bulk IBM, while likely is still  more robust than the vast majority of keyboards out there even id not on par with a standard model M, all with a price comparable with the one from an average RD


Hardly one can ask more
The problem with quotes on the Internet is you never know if they are true  (Abraham Lincoln)

Offline jpc

  • Posts: 363
Repairing the IBM Model M2
« Reply #91 on: Sat, 09 July 2011, 19:45:55 »
Quote from: The Solutor;376826
Hardly one can ask more

 
I'd like it to work too ;)

RSI prevention recipe:[/B] Kinesis Contoured, Colemak layout, touch typing, Contour Design Rollermouse,  Logitech TrackMan Wheel, Logitech m570 trackball, "workrave" break timer software, "awesome" window manager, tenkeyless boards, cherry browns, Wang 724 with "ghetto green" ALPS, standing desk and/or comfy adjustable chairs, stress reduction, computer time reduction.

Fun non-ergonomic things: bolt modded Model M Space Saving Keyboards with new springs, Kensington Expert Mouse v7, Unicomp Endurapro, Northgates

Offline The Solutor

  • Posts: 2262
Repairing the IBM Model M2
« Reply #92 on: Sun, 10 July 2011, 15:43:14 »
Quote from: jpc;377088
I'd like it to work too ;)

 
A couple of electrolytic ona 20+ years old device are not such wonder, remember the maynboards sold around 2000/2003 by most top brands (IBM included) an died after one or two years of usage due to the cheap capacitors used ?

BTW Reading your previous message i bet you don't have a not working trace, but a missing contact between the membrane and the PCB, have you tried to clean the contacts ?
The problem with quotes on the Internet is you never know if they are true  (Abraham Lincoln)

Offline jpc

  • Posts: 363
Repairing the IBM Model M2
« Reply #93 on: Sun, 10 July 2011, 19:54:05 »
Yes, after repairing two traces, there was a weak contact between one of the traces and the controller. This persisted after cleaning the contacts gently with a soft pencil eraser.

By holding down the controller, every key can be made to work. So I will try to replace the foam strip beneath the controller with something that will put a little more force on the membrane. That foam strip has been squashed in place for 20 years and it's no good anymore.

RSI prevention recipe:[/B] Kinesis Contoured, Colemak layout, touch typing, Contour Design Rollermouse,  Logitech TrackMan Wheel, Logitech m570 trackball, "workrave" break timer software, "awesome" window manager, tenkeyless boards, cherry browns, Wang 724 with "ghetto green" ALPS, standing desk and/or comfy adjustable chairs, stress reduction, computer time reduction.

Fun non-ergonomic things: bolt modded Model M Space Saving Keyboards with new springs, Kensington Expert Mouse v7, Unicomp Endurapro, Northgates

Offline The Solutor

  • Posts: 2262
Repairing the IBM Model M2
« Reply #94 on: Sun, 10 July 2011, 20:03:34 »
Quote
So I will try to replace the foam strip beneath the controller with something that will put a little more force on the membrane. That foam strip has been squashed in place for 20 years and it's no good anymore.


Definitely the way to go
The problem with quotes on the Internet is you never know if they are true  (Abraham Lincoln)

Offline Half-Saint

  • Posts: 371
Repairing the IBM Model M2
« Reply #95 on: Mon, 11 July 2011, 07:36:55 »
The latches that hold the controller PCB tight against the membrane have to be the most idiotic patent ever. Same crap with fixed cable model Ms! I have one M2 which probably suffered multiple drops to the office floor and most of the latches are gone. There is almost no contact between the membrane and the PCB. The only thing I can think of that would help is probably conductive glue of some sort... any other ideas?
IBM Model M (6) - Acer Alcatel 6312-KW - IBM Model M Space Saver - IBM Model M 122-key - Cherry G80-3000 (2) - IBM Model F AT - TG3 BL82A (2)

[SIGPIC][/SIGPIC]
_______________________________________________
My geek blog: http://onlyageek.blogspot.com/
Flickr: http://www.flickr.com/photos/mr_mayhem/

Offline The Solutor

  • Posts: 2262
Repairing the IBM Model M2
« Reply #96 on: Mon, 11 July 2011, 07:48:48 »
Quote
any other ideas?


A piece of adhesive rubber foam glued to the upper half of the housing ?
The problem with quotes on the Internet is you never know if they are true  (Abraham Lincoln)

Offline AIM-9X

  • Posts: 2
Repairing the IBM Model M2
« Reply #97 on: Sun, 24 July 2011, 17:43:05 »
I have repaired several more of these keyboards in recent months and have noticed two primary types of failures among these keyboards.  The first common problem of stuck LEDs is in fact caused by the dried capacitor(s) mentioned in this thread (in my experience, a dried 2.2 uF capacitor causes the LEDs to stick).  The second problem deals with stuck keys.

For those who have the M2 keyboard and are experiencing the 'stuck key' problem:

This problem is ==>NOT<== caused by the rubber mat, or the 'membrane,' as it is sometimes called, and if the mat has any remote effect, it is minor.  I would highly recommend not wasting time trying to find a replacement rubber mat or 'membrane.'  You will only get more frustrated.  The rubber mat has two jobs:

1. Transmit the force of the spring/pivot assembly (the key force) to the two plastic circuit sheets in order to adjoin them (thereby closing the circuit and generating a keystroke).
2.  Provide a friction surface for the spring pivots (the tiny plastic piece that the spring is attached to) so that they don't slide around.

On this keyboard there are two thin plastic printed circuit sheets that contain the key switches:  an upper sheet for the upper halves of the key switches and a lower sheet for (obviously) the lower halves of the key switches.  Between these switch sheets lies a critical sheet that maintains a very small gap between the upper and lower key switch sheets.  This "gap sheet" just has a bunch of holes punched through it, and the holes align with each of the switches.

to illustrate (horribly) with ASCII characters:  Here is a schematic of a cross-section view of the rubber mat and circuit sheets:

-----------------------
rubber mat
-----------------------

++++++++++++++
upper switch sheet
++++++++++++++

~~~~~~~~~~~~
GAP SHEET
~~~~~~~~~~~~

++++++++++++++
lower switch sheet
++++++++++++++

The gap/spacing between the circuit sheets is critical.  Normally, the gap sheet does its job and provides a large enough switch gap that no keystroke is generated when the keyboard is not being used.  Over time, and with frequent assemblies and disassemblies, the gaps between the switches can shrink enough to cause one or more key switches to remain closed, always registering a keystroke.  It is more difficult to diagnose when the , or other non-lettered keys are stuck, and it takes considerable testing to figure out which specific keystroke circuits are affected.  Generally, if one key is affected, it is entirely possible that those near it are also affected.  

Common symptoms of stuck keys are:

1.  indefinitely repeating characters
2.  more than one character generated in a keystroke
3.  keystrokes generating the wrong characters
4.  keystrokes registering before the click of the buckling spring
5.  completely non-functional keyboard (you see the LEDs properly flash once plugged into a computer, but keystrokes do nothing)
 

To test this out, disassemble the keyboard according to the instructions in this thread (remove the screws, pop the keys off, push the snaps aside, pry it in half), and remove the rubber mat.  Plug the PS/2 connector into a PS/2-to-USB active signal converter and plug it into a modern PC.  Use some sort of text editor and press the individual dots on the key switch circuit sheets.  Each key should register properly.  The problem occurs after you re-assemble everything.  You plug it in, watch the LEDs do their usual flash, and then you experience one of the symptoms above.  This is where the gap problem arises.

Try to determine what area of the keyboard is affected.  This may take a few assemblies and disassemblies, but if you are able to locate the affected area, here's what I did:

You solve this problem by increasing the gap between the upper and lower switch circuit sheets.  The upper and lower circuit sheets have the printed dots and lines on them (this is really just one single sheet that is folded in half).  When you determine the affected area, place thin pieces of scotch tape on the center or bottom sheet (the sheet with holes in it, or the sheet with the bottom switch halves) around each affected switch, being cautious to apply tape **around** but not **directly between** the switches (if you tape directly between the switches, you completely prevent the switch from closing--never do this).  If you want to avoid this problem, apply tape only to the gap sheet and DO NOT cover any of the holes.  The tape effectively increases the gap, which allows the key switch to remain open when not in use.

For example, on one M2 keyboard I repaired, I noticed that the a, s, d, z, x, and c keys were acting strange.  I'd plug the keyboard in and see one or more of these keys repeated in my text editor window, or I'd not get a keystroke at all, or I'd get two or three characters rather than the one I asked for.  At times, I would barely press a key and still get a keystroke.  I disassembled the keyboard and placed strips of scotch tape around each of the switches in that particular area (the entire lower left area of the keyboard).  I put everything back together and there were no more stuck keys.

This has worked every time without failure.

Offline npkrol

  • Posts: 1
Repairing the IBM Model M2
« Reply #98 on: Mon, 05 September 2011, 03:03:53 »
Ive got brand new (packed ) model m2 1989 keyboard. Works just fine. What are the chances it will suddenly break? :)

Offline lowpoly

  • Thread Starter
  • Posts: 1749
Repairing the IBM Model M2
« Reply #99 on: Mon, 05 September 2011, 15:07:03 »
Quote from: AIM-9X;386381
This problem is ==>NOT<== caused by the rubber mat, or the 'membrane,' as it is sometimes called, and if the mat has any remote effect, it is minor.

Good problem solving with the stuck keys. The rubber mat is not the membrane, btw.

Quote from: AIM-9X;386381
On this keyboard there are two thin plastic printed circuit sheets that contain the key switches

This is.

Miniguru thread at GH // The Apple M0110 Today

Offline chupanibre

  • Posts: 7
Repairing the IBM Model M2
« Reply #100 on: Thu, 01 December 2011, 06:02:57 »
hey, i just wanted to say thanks for this article!
this message was typed on a previously broken m2.