Author Topic: IBM model M strange behaviour [SOLVED]  (Read 1546 times)

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Offline Sodor

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IBM model M strange behaviour [SOLVED]
« on: Tue, 13 April 2021, 01:10:00 »
Hi, I have a IBM model M that I use on work, recently I repaired a silver trace with copperfoil and do the "nut and bolt" mod, tested all the keys and worked OK, after two days of no use (weekend) I arrived to work, power on the PC and noticed that numeric row keys don't work, but after four or six smooth keystrokes to keys 1 and 2 all the numeric row keys begin to work, then I lef the PC for about 5 hours, when I return the same problem appear again and the solution was the same: four to six smooth keystrokes and all the numbers begin to work again, no need to hit the keyboard or to use much pressure on keystrokes, and the remaining 2 hours of work the keyboard worked fine, I don't know why it behave like that, I don't know if tomorrow when I arrive to work will happen again, is there anyone that have the same detail before? and if someone know what could be causing it and how can be solved, thanks.



« Last Edit: Fri, 23 April 2021, 15:51:19 by Sodor »

Offline yui

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Re: IBM model M strange behaviour
« Reply #1 on: Tue, 13 April 2021, 01:40:32 »
would it be that your copper tape is not sticking well and when you press 1 and 2 you get it to stick properly again? i know unicomp sells new membranes for rather cheap (12 or 20 USD, do not remember) so that may be your ticket, or better copper tape.
vi vi vi - the roman number of the beast (Plan9 fortune)

Offline Sodor

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Re: IBM model M strange behaviour
« Reply #2 on: Tue, 13 April 2021, 02:05:34 »
Thanks yui, I don't think that's the problem, the copper foil isn't near those keys plus I don't have to use much force when I hit numeric keys to (if that would be the case) make the copper foil make contact with the silver trace, also the problem would be more intermitent within use of the keyboard if there are bad contac between copper foil and silver trace, anyway I will check if the repaired trace is related to those keys.

Offline yui

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Re: IBM model M strange behaviour
« Reply #3 on: Tue, 13 April 2021, 02:51:14 »
not knowing where your reapair is it was the easiest explanation, so i tried :)
vi vi vi - the roman number of the beast (Plan9 fortune)

Offline Sodor

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Re: IBM model M strange behaviour
« Reply #4 on: Tue, 13 April 2021, 18:37:08 »
Well, today was the same... BUT I located the problem only on 1 2 3 4 7 8 9 0 keys, and with smooth keystrokes those keys where working again... So I will dissasemble it to view if the repaired trace is related to those keys as I said before.

Offline Maledicted

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Re: IBM model M strange behaviour
« Reply #5 on: Tue, 13 April 2021, 21:10:15 »
I have never bolt modded a Model M, but I think Fohat (who's worked with buckling spring of all kinds for a long time) has always recommended that bolts are around finger tight. Maybe the bolts near the lip of either end of the plate sandwich are too tight?

Offline Sodor

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Re: IBM model M strange behaviour
« Reply #6 on: Tue, 20 April 2021, 12:39:22 »
Thank guys for your time, the problem is apparently solved, testing traces related to malfunction keys I localized the problem to connector edge on one of the membranes, the silver conductive ink was eroded on multiple traces, so it wont make adecuate contact to connector pins, I used copper foil to fix that and tested multiple times on two PC, by today are two days without problems, If no problems appear by friday I will change the title of this post to SOLVED.

Here the image of the membrane with problems:


To fixit I use copper foil and I paste it with contact glue for shoes, leather, etc... and kapton tape to not expose the conductive ink traces to solvent from glue http://www.vl2000.com/project/vl-2000-negro/


Finally here are the membrane assembly (with a previus fix):



Offline Maledicted

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Re: IBM model M strange behaviour
« Reply #7 on: Tue, 20 April 2021, 12:43:49 »
That's awesome.  :thumb: Thanks for sharing.

How did the traces wear so badly to begin with?

Offline Sodor

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Re: IBM model M strange behaviour
« Reply #8 on: Thu, 22 April 2021, 13:44:23 »
Was my fault, this keyboard was given to me for free, and some of the palstic rivets where break, because of this some keys where not working unless some pressure was applied, initially I have no idea that was the cause so I thought that membrane edge connectors have bad connection due silver oxidation (black color) so I use a rubber to clean, I used too many pressure and some of the silver ink was "erased" so I don't continued with the other membrane, that was the first problem  :-[ , then I learn about nut bolt mod and on that moment I realized that problem was because lack of pressure by the broken plastic rivets, I ordered all to do the mod, after 3 month of wait nothing arrived so I opted for other solution, an experiment, I use a mix of acetone and ABS plastic know as ABS slurry (https://www.matterhackers.com/news/how-to-make-abs-juice-glue-and-slurry) to remake the broken rivets... and it WORK!!! but was a partial success, this because the eroded silver ink trace on edge connector was causing problems and some keys works but then it doesn't work, but I didn't realized that and I thought that I don't used the necesary pressure when I was applying the ABS slurry, the bolts and nuts arrived.... So I remove all the ABS slurry to do the nut and bolt mod, only to see that some ABS slurry entered between two membranes, was easy to clean but some was struk over a silver ink trace and when I remove the plastic also remove part of the trace  :(, I used copper foil and kapton tape, that fix that problem, I assembled all and problems was still present and the rest of this history is know on the previous post...

So Folks, for general knowledge this history is about what NOT TO DO to attepmt to fix a IBM model M keyboard, it also reafirm that bolt and nut mod is the BEST to fix problems with bad plastic rivets and show how tough a IBM model M keyboard is, afther that burden it can be fixed and work again.
« Last Edit: Thu, 22 April 2021, 13:52:16 by Sodor »

Offline Maledicted

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Re: IBM model M strange behaviour
« Reply #9 on: Thu, 22 April 2021, 13:55:00 »
You may know this, but Unicomp sells replacement membranes and mats for the Model M. Some people prefer the modern mat material to the originals. Since you've already bolt modded yours anyway, it might not be a bad idea to pick something up from them to play with.

Offline Sodor

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Re: IBM model M strange behaviour
« Reply #10 on: Fri, 23 April 2021, 15:50:41 »
Thanks for the advice, yes I know it, I will consider it if the membranes goes beyond any fix I can do  ;), Also by now my keyboard can be considered fixed  :), thanks to all.