Problems with an IBM M4-1

[ch_123]

Hello all,

I acquired a German-layout IBM Model M4-1 (1379595, dated 12-SEP-93) from eBay. However, when I got it, I found that a large amount of the keys are completely non-functional (so far I've found - everything along the number row except backspace, two of the arrow keys, about half of the F keys, all of the keys above the arrow keys (home/delete etc) and the left control key) I have contacted the seller about this, and have pointed out that I'm less than impressed that his "Perfectly functional" keyboard is all but useless. However, I do really like the keyboard, and considering that its the only ISO/European layout M4-1 I've ever seen, I'd rather like to try and figure out what's wrong with it than send it back. I opened it up, detached and re-attached all the cables inside it, which had no effect. Everything seemed to be in very good shape - there was no sign of anything being damaged or broken. Whilst I appreciate that the keyboard is rather old, and isn't quite as tank-like as a Model M, it seems a bit odd that entire rows of keys would just stop functioning, and others not.

So, any ideas I know it's a bit of a long shot, but if there's anything that can be done, I'm sure someone around here might know about it!

[iMav]

Unicomp may be able to refurbish it for you.  I'd give Jim a call.  They still make M4's and, up until a few years ago, made the M4-1 as well.

[ch_123]

THREAD NECROMANCY!

I dusted it off and disassembled it fully - the membrane had a few fried traces. I've had success with a silver gel PCB trace repair pen, and the affected keys on the traces I have fixed are back in action... Expect a guide soon.

[itlnstln]

Awesome.  Glad to hear you got it fixed.  When should we expect the guide?  Some time around November 2011?

[ch_123]

Whenever Unicomp releases their buckling spring M4-1.

[ch_123]

Update: The keyboard is now in fully functional operation - the problem was a far more simpler one than I imagined, and one that potentially affects all Model M type keyboards.

Those who have dismantled Model Ms before will notice that the contacts on the ribbon cable for the controller start to wear out (a black layer forms on the contact). It is normal for there to be at least some of this stuff built up on the contact of an old IBM keyboard, but in this case, it had built up so much that the controller couldn't 'see' the trace.

Fortunately, between the start of the contact and the end of the ribbon cable, there is a bit of exposed trace that didn't corrode for whatever reason. Getting the silver pen, and drawing in a new contact starting just above it fixed the problem. I have at least one other Model M that suffers this issue, so I think this a pertinent issue with these keyboards that should be conisdered during the diagnosis of problems.

[kriminal]

noted, thanks for the info...

[ch_123]

Repaired my IBM SSK, which had two dead rows due to the same problem.

This proved to be a tougher adversary - the contact actually starts inside the ribbon cable, so there was no place to run the trace off. So, I had to 'draw' a new trace on top of the ribbon cable to connect the new contact I made. The ribbon cable was covered by thicker green plastic of a different consistency, so it was a bit tricker to link the trace to the pre-existing one compared to when I tried to do the same on the M4-1 trace.

The other issue with exposed traces on the ribbon cable is that you could get shorting with the backplate. Mine were on the ribbon cable that faced away from the backplate, but there's also the issue of potential aerial erosion. I might devise a protective cover for it out of clingfilm tomorrow just to be sure.