Author Topic: Repairing the IBM Model M2  (Read 54327 times)

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Offline rdh

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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

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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

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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

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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

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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.
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Offline lowpoly

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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?

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Offline Qwertyuiop

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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.
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Offline quadibloc

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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

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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

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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

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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

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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.
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Offline chozar

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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

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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

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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

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« 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 »
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Offline Rajagra

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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

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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.

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Offline Hydron

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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

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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.
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Offline Hydron

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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

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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

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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.)
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Offline fsck

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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

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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

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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

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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.
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Offline Tables

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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

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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

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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

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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^^.
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Offline mich

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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

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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.
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Offline mich

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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

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« 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
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Offline Cern33

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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

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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!

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Offline Touch_It

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« 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


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Offline jpc

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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

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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

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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
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Offline jpc

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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

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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

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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

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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

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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?
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Offline The Solutor

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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

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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

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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.

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