Repairing a Model M2.

[-Space-NATO-]

Hello guys! I just bought an 1992 IBM Model M2. It came super dirty.

     As I plug it in (Via an active converter), the 3 lights turn on for a second and only the numlock light stays on, if i click on the numlock key the light turns off but it wont register. The minority of the keys register the others don't. T Y G H B N and some symbols are the only keys that register. I dont want to start the restoration not knowing whats the problem and leave it midway.

    Ive read that the capacitors need to be changed (Probably thats the problem) and sometimes the traces are corroded. (Cant find a way to solve that.). Does anyone got the same problem? anyone manage to bring this board from the dead? any help is appreciated! thank you very much for reading.

[yui]

M2s are like model Ms with some extra electrical gremlins (bad caps), given your symptoms i would either expect broken rivets (20+years old plastics rivets will break) or a damaged membrane (maybe from liquid spilled on it), usually, from what I've read bad caps will make it not function at all.
I would start my checking for broken rivets on the back of the membrane assembly, next caps are cheap and easy to replace so if you do not find broken rivets near the non working keys i would change them, and then it would be time to disable the sandwich to check the membrane. or wait for fohat to weigh in, he seems to be the expert of model M around here

[-Space-NATO-]

M2s are like model Ms with some extra electrical gremlins (bad caps), given your symptoms i would either expect broken rivets (20+years old plastics rivets will break) or a damaged membrane (maybe from liquid spilled on it), usually, from what I've read bad caps will make it not function at all.
I would start my checking for broken rivets on the back of the membrane assembly, next caps are cheap and easy to replace so if you do not find broken rivets near the non working keys i would change them, and then it would be time to disable the sandwich to check the membrane. or wait for fohat to weigh in, he seems to be the expert of model M around here

Thanks for the reply! I have open the keyboard, The M2 dont have a metal plate so there are no plastic rivets like the model M, it does have some plastic clips that holds the back and front case together, fortunately i didn't break any on the disassembly. I can see some corrosion on the capacitors, i've already bought some replacements. Membrane seems fine, can't find any corrosion or gunk on it but ill will clean it with some isopropyl alcohol. Later Ill post some photos of the progress.

[-Space-NATO-]

Here is the PCB. Corrosion is clearly visible, hopefully changing the capacitors is the solution.

[yui]

yeah, looks like it, hopefully the pcb is not damaged as well, i should really get myself an M2, would not have gone from random things i've read around on forums and they seem somewhat easier to mod compared to other Ms, only thing is that they are hared to find in iso-US and M keys do not fit on them, at least from what i've read.

[-Space-NATO-]

Yes i fix it!... kinda. Typing this text on the Model M2. There is a problem with the numer 6 on the keypad, if i put the keycap on it register constantly, but if i tap on the spring it regsiters just fine. Ive manage o attach the keycap in a wrong way, it registers but dont sound correct (The ping is way more quiet).

Ill be posting a post of the full proccess of restorarion in the next few days!

[yui]

i have the same problem on one of my unicomp 122, if you find the reason why it does that it would be nice to know, mine is on the =+ key on the number row as well, i have tried with neighboring working caps but it still only faintly clicks and not always register and the cap works on other keys.

[-Space-NATO-]

I think that the contact membranes are too close to one another, maybe some dirt got stuck under the membranes just in that spot and forced the membrames  closer together idk.

Did you open your unicomp 122?

[yui]

i did not open this particular one, as it is new and it is the only problem with it, so it is last in the list of keyboard to fix (i have 3 other that i bought to train myself on fixing those things, so far only one is fixed and 2 other are in pieces...), i am using it right now and as i still can have the character i still have not taken the courage to try to fix it.