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Author Topic: new model M not working  (Read 2178 times)

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Offline Truhammer

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new model M not working
« on: Fri, 27 May 2016, 23:57:46 »
Hi all, I bought a practically new model M 52G9700 made by Lexmark 1993 for 20 bucks on Craigs, the catch was a few keys do not work. It had been used once and put in a cupboard with no box for its lifespan. I don't know word one about testing these. If anyone could lead me down the right path I'd really appreciate it. I opened the case with a nut driver I modelled and 3d printed, attached if anyone wants it. The inside is mint, all rivets intact.

They keys which don't work are F3 F7 { } Backspace CapsLock Tab T Y and numpad 4 5 6 .. so somewhat grouped?
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Offline E TwentyNine

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Re: new model M not working
« Reply #1 on: Sat, 28 May 2016, 06:55:13 »
You have a issue with a trace.  You'll want to reset the ribbon connectors in the controller board before you do anything else.  Your issue is with the second from the left trace on the smaller ribbon:



You may as well reseat them both - do not attempt to clean them with anything harsh or scrub them.

If reseating doesn't work you have a break in the trace somewhere which may be fixable without a bolt mod depending on where it is.  Since the whole trace is out it's above the F7 key, likely where the membrane transitions to the connector and that extra support is there, sometimes cracks right there. 
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Daily driver: SSK or Tenkeyless IBM AT
1984 Model M Industrial Prototype ⌨ 1992 Black Oval Industrial SSK ⌨ 1982 5251 Beam Spring ⌨ 89 Key "SSK" ⌨ M13 triplets

Offline Truhammer

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Re: new model M not working
« Reply #2 on: Sat, 28 May 2016, 09:40:21 »
You nailed it, very interesting. I have re-seated both, no luck. Visually they both look great but like you said since it's the entire trace it must be above F7. What would you recommend next? I've read a few ideas.. trace pen, copper tape .. Could the ribbon receiving end on the board be the problem?

Since it's never been used and the rivets are fine I wanted to avoid the bolt mod, but if nothing works I'd need a new membrane sheet from unicomp correct?

Thanks again
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Offline E TwentyNine

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Re: new model M not working
« Reply #3 on: Sat, 28 May 2016, 10:22:14 »
Get a multimeter and check for continuity between the tip of the trace and an exposed section below the connector.  You should find a loss somewhere.

Before you do that you may want to take a very close look at it, especially where the reinforced connector ends.  I find it a little odd the second trace went and the first one didn't (if it did in fact go).

If you want to test the controller itself, pull both ribbons out, plug the keyboard in, and get a piece of wire. Jumper the second pin in on the smaller connector to various pins on the larger one, see if keys register.
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Daily driver: SSK or Tenkeyless IBM AT
1984 Model M Industrial Prototype ⌨ 1992 Black Oval Industrial SSK ⌨ 1982 5251 Beam Spring ⌨ 89 Key "SSK" ⌨ M13 triplets

Offline Truhammer

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Re: new model M not working
« Reply #4 on: Sun, 29 May 2016, 14:23:42 »
Quote from: E TwentyNine on Sat, 28 May 2016, 10:22:14
between the tip of the trace and an exposed section below the connector.

Do you mean i need to cut away the membrane sheet to expose the trace? Only 1/4" or so of the trace is exposed at the tip. I tested the continuity there and it worked.
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Offline Snowdog993

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Re: new model M not working
« Reply #5 on: Mon, 30 May 2016, 16:13:35 »
Quote from: Truhammer on Sun, 29 May 2016, 14:23:42
Quote from: E TwentyNine on Sat, 28 May 2016, 10:22:14
between the tip of the trace and an exposed section below the connector.

Do you mean i need to cut away the membrane sheet to expose the trace? Only 1/4" or so of the trace is exposed at the tip. I tested the continuity there and it worked.

If the continuity is good, and the controller is good, the contacts on the membrane to the controller is the problem.  You can use a pencil eraser on the contacts and try reconnecting it.
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Offline E TwentyNine

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Re: new model M not working
« Reply #6 on: Mon, 30 May 2016, 16:17:12 »
Quote from: Truhammer on Sun, 29 May 2016, 14:23:42
Quote from: E TwentyNine on Sat, 28 May 2016, 10:22:14
between the tip of the trace and an exposed section below the connector.

Do you mean i need to cut away the membrane sheet to expose the trace? Only 1/4" or so of the trace is exposed at the tip. I tested the continuity there and it worked.

No, definitely not.  Try the wire jumper between the sockets first to make sure it's not the controller.

Regarding the membrane, you should be able to reach an the exposed trace, and if not you can snake a thin strand of wire in there and try it.  Big SHOULD there.  I'd have to take a look at an assembled keyboard assembly to see how you'd want to do it specifically, but it is possible.  I've even managed to snake a wire between the metal backplate and barrel plate to repair a trace without a bolt mod.
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Daily driver: SSK or Tenkeyless IBM AT
1984 Model M Industrial Prototype ⌨ 1992 Black Oval Industrial SSK ⌨ 1982 5251 Beam Spring ⌨ 89 Key "SSK" ⌨ M13 triplets

Offline Truhammer

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Re: new model M not working
« Reply #7 on: Sat, 04 June 2016, 15:20:17 »
Thanks for all the tips .. I tried the silver pen on the exposed section near the tip and it fixed the broken trace.
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Offline E TwentyNine

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Re: new model M not working
« Reply #8 on: Sat, 04 June 2016, 16:20:03 »
Quote from: Truhammer on Sat, 04 June 2016, 15:20:17
Thanks for all the tips .. I tried the silver pen on the exposed section near the tip and it fixed the broken trace.

Great.   Keep it mind that after a few months it may fail again.  Keep the pen handy.  Should be a 5 minute fix if it happens again.

I have a keyboard like this, has lasted a year since the last fix, probably the third time I fixed it that way, just haven't gotten around to doing it properly.
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Daily driver: SSK or Tenkeyless IBM AT
1984 Model M Industrial Prototype ⌨ 1992 Black Oval Industrial SSK ⌨ 1982 5251 Beam Spring ⌨ 89 Key "SSK" ⌨ M13 triplets

Offline Truhammer

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  • Posts: 5
Re: new model M not working
« Reply #9 on: Sat, 04 June 2016, 18:23:48 »
Ok, so just top it off then eh .. by the way...

the keyboard had the original PS2 to usb adapter, and will only work if it is plugged into the usb port and the computer is restarted or turned on. Unplug it while it is on and plug back in, it no longer responds. I doubt all model Ms work like this but I'm guessing. Would this likely be a passive adapter? Maybe an active adapter would fix this?
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Offline rowdy

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Re: new model M not working
« Reply #10 on: Sun, 05 June 2016, 01:09:31 »
I use one of these with some of my Model M keyboards and my Mac: http://techkeys.us/collections/accessories/products/usb-to-ps2-serial-multimode-adapter

Works perfectly each time without having to restart the Mac.
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Offline Hellmark

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Re: new model M not working
« Reply #11 on: Thu, 09 June 2016, 13:23:20 »
USB is hot pluggable. Something is not right if you have to reboot to have it work. The passive adapters I've seen usually went USB to PS/2 and not the other way around.
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