'94 Model M - Garbled characters when typing

[tomie]

Hello folks.

I'll move past the obligatory "I'm new" here and get to my problem : When I type certain keys, the keyboard prints out the correct character but also 'garbage' additional characters... Not all keys are doing this, mainly just the S key (prints 's/') and both H and J (prints 'hj').

At first I thought it was my USB->PS/2 adapter, so I plugged the keyboard into old trusty (WinXP ASrock AGP Desktop) and the problem persisted...

I'm wondering if anyone has ran into a problem like this before? I tried my hand at Google-fu but I didn't find the exact same problem I am having.
One thing I did find is someone who had a similar Model M, all of his keys were printing random characters. I read further and it seemed like people were suggesting to replace the PS/2 cable, and do a "bolt mod"(?).

My guess was maybe bad capacitors, but I have never opened up this keyboard so I am not sure what the insides look like. I'm probably really wrong.

Any advice?
Thank you.

IBM Model M
11 May 1994
Part No: 82G2383
ID No : 0138948

[Weezer]

There's about a 90% chance that it's bad traces and about a 10% chance that it's something else.

[tomie]

There's about a 90% chance that it's bad traces and about a 10% chance that it's something else.

Thank you for your reply.
I presume this is on the membrane? If such is the case, I'd either have to hunt down the faulty traces or order a new membrane, correct?

[kelvinhall05]

There's about a 90% chance that it's bad traces and about a 10% chance that it's something else.

There's about a 90% chance you're full of shit lel


OP I'm guessing either the rivets are gone and it needs a bolt mod, or you/someone else did a bolt mod and the bolts are too tight.

[tomie]

There's about a 90% chance that it's bad traces and about a 10% chance that it's something else.

There's about a 90% chance you're full of shit lel


OP I'm guessing either the rivets are gone and it needs a bolt mod, or you/someone else did a bolt mod and the bolts are too tight.

Previous owner definitely didn't crack this thing open. The bolt mod looks very difficult, I'm not sure of the exact hardware I need

[Lalaland124]

Previous owner definitely didn't crack this thing open. The bolt mod looks very difficult, I'm not sure of the exact hardware I need

It's not that difficult, In my opinion it looks more difficult than it actually is. Although if you've never done anything crafting related I would be careful. Important is that you have the right screws and right drill bit. There are a few tutorials online that you can watch before unscrewing anything Just take your time and double check the tutorials if you are not sure. And take pictures of how everything is fitted together before you take it apart.

However, that's just my opinion so you have to decide for yourself if it's worth taking the risk, will be a fun project for sure tho

Good luck!

[Muirium]

The one bolt mod I ever did felt like more work than building an entire new keyboard. And I have indeed built a few keyboards from scratch! Some people are into doing bolt mods but definitely not a task for all of us. I advise ruling everything else out first.

So: first check the capacitors. You’ll need a nut spinner (5.5 mm isn’t it?) to open the case. You can also very easily pull out the ribbon cables while you’re in there and plug them back in again. Replacement Model M controllers are a thing. Everything that isn’t stuck between those damn plastic rivets is right at your immediate disposal.

Oh yeah: does the board make noise when you shake it? The more broken rivets, the more it needs a bolt mod.

[Lalaland124]

Oh yeah: does the board make noise when you shake it? The more broken rivets, the more it needs a bolt mod.

That's right I would try doing that! Maybe you don't have to do the mod after all

[tomie]

Hi all. Thank you so much for your help!

I shook the keyboard and aside from what sounded like buckling springs moving around a bit, I heard no loose plastic from within the keyboard. I assume it would sound almost like crumbs stuck in something,right?

Edit: I will take it apart this afternoon and look for any visual damage and check to see if the caps are leaking their conductive goo. But I have a feeling that it could be the membrane...

[feltel]

Capacitor leakage is a problem which exists only on the Model M2. All other Ms are safe in this regard.

[Muirium]

But membrane, really? Since when do those go wrong?

[feltel]

Water or other liquid which gets spilled over the keys and find its way into the backplate-membrane-barrel plate sandwich.

[Thorogrimm]

But membrane, really? Since when do those go wrong?

I had a burnt/dirty tracer on an Olivetti that I own

[kelvinhall05]

But membrane, really? Since when do those go wrong?

The membrane itself basically never fails, it's always external factors, usually water.

[tomie]

I haven't been able to open it as I don't seem to have the right size of tool to get into it...
Someone mentioned it was 5.5mm nut spinner. It seems to make sense as 5mm was too small and 6mm was too big.

[Weezer]

There's about a 90% chance that it's bad traces and about a 10% chance that it's something else.

There's about a 90% chance you're full of shit lel

Feel free to disagree with me all you like, but there's no reason to be an ass.

The membranes are the #1 point of electrical failure in a Model M because they oxidize easily through exposure to humidity or because of slight water exposure.

I highly doubt that it's an issue of bad rivets, because usually the rivets coming off negatively impacts key feel in a noticeable way, and when the keys fail, they will stop registering, or start registering multiple times, not trigger other keys down the trace, clear across the keyboard.

It's not a cap issue because only M2s suffer from cap issues, and a bad cap wouldn't cause keys to register when they're not pressed, it would likely take out the entire circuit.

[kelvinhall05]

There's about a 90% chance that it's bad traces and about a 10% chance that it's something else.

There's about a 90% chance you're full of shit lel

Feel free to disagree with me all you like, but there's no reason to be an ass.

The membranes are the #1 point of electrical failure in a Model M because they oxidize easily through exposure to humidity or because of slight water exposure.

I highly doubt that it's an issue of bad rivets, because usually the rivets coming off negatively impacts key feel in a noticeable way, and when the keys fail, they will stop registering, or start registering multiple times, not trigger other keys down the trace, clear across the keyboard.

It's not a cap issue because only M2s suffer from cap issues, and a bad cap wouldn't cause keys to register when they're not pressed, it would likely take out the entire circuit.

My bad, did not mean to come across so harsh.

If the pads were oxidized then keys would work intermittently, not press multiple keys that are physically right next to them on the board. I've seen this exact issue on both badly bolt modded Ms and ones that need a bolt mod (whether it's due to rivets falling out or water damage, or even both). Even if it was pad oxidiation it's not trace *failure* as it can be cleaned with a qtip and rubbing alcohol.

I also agree it is not bad capacitors, even if they were a known failure point it would not explain this behaviour.

[Weezer]

My bad, did not mean to come across so harsh.

No worries lol It's no biggie.

We'll have to see what the issue is when OP is able to take their keyboard apart and post some pics