Repairing an M0110 Macintosh Plus keyboard

[bigmessowires]

My M0110 was working perfectly three days ago, two days ago the S key stopped working, then yesterday the whole keyboard stopped working. I guessed it was probably a bad connector where the cable plugs in, but wiggling and poking at it doesn't seem to help. Today after many attempts at unplugging and replugging the keyboard I got it to work for about two seconds until it died again.

Anybody know what the common failure points are for a whole keyboard failure? Most of the M0110 discussion I've seen revolves around repairing specific keys on a keyboard that otherwise works. The keyboard only has two ICs and a small number of caps, and none of those pesky SMD electrolytics. I disassembled the keyboard and the inside looks good visually, with no obvious coffee spills or signs of trouble. With the keyboard case removed, I tried poking at different areas with a plastic tool while the Mac was running, but nothing I did helped return it to life.

 

[bigmessowires]

Is the schematic for M0110 or M0110A available anywhere?

 

[Iesca]

Sounds like an intermittent cable, I would start with that. People sell new ones on ebay for not too much.

 

[bigmessowires]

I forgot to mention I have a second M0110 that works OK (except two broken keys) with this same cable. It could be the cable connector, but in that case I would have expected wiggling and poking it to produce some signs of life. The way the keyboard went from working to partly working to dead in three days makes me suspect a component failure. I'll get a logic analzyer on some pins and see what I can see.

 

[Iesca]

Oof, good luck.

 

[bigmessowires]

The plot thickens. I had the keyboard connected, top cover removed, Mac on and running the Key Caps control panel. It still wasn't working. I walked to my desk to grab my multimeter, and from across the room I saw the Key Caps window change from the M0110A layout (which I think it shows by default) to the M0110, and the keyboard began working again (except for the S key). I tugged and prodded and wiggled both ends of the cable and it continued to work, so I'll say it's definitely not a cable problem.

Restarted the computer and the keyboard continued to work. Picked up the keyboard, shook it, and banged it on the desk - still working. Pressed on the keyboard ICs with my finger - still working. Pressed on all the capacitors I can see - still working. Turned off the computer, unplugged the keyboard cable, plugged it back in, waited 2-3 minutes, turned the computer back on - still working, and now the S key is working again! S needs to be hit slightly harder than other keys in order to register, but it works.

I'm at a loss to explain this. Maybe something temperature-sensitive? Some moisture inside the keyboard that needed time to evaporate? I guess it's my lucky day!

EDIT: and now the S key is working fully with no extra force needed. Best keyboard repair job ever!

 

[Iesca]

Wizard repair!