Wyse PCe glitching?

[drevyek]

I have a beautiful Wyse PCE keyboard that I am trying to restore, and (after cleaning the switches and putting it all back together) I've found that it starts to glitch after a little bit of typing. Sometimes after plugging in, it just doesn't register any keypresses, but that is solved with plugging it back in a few times.

I'll try typing a few characters, and it will then spew out random keypresses (either a repetition of the same key, or random keys). Has anyone experienced something like this?

My first thought is the capacitors on the board being old and worn out. There are a handful of the small ceramics, and a pair of electrolytics. The PCB was in really rough shape when I got to it, but all of the keys do work.

[Muirium]

Electrolytic capacitors should always be considered suspect. The fact your board's working fine for a little while, then goes wrong, also points to them. They sound like they're only barely still working, having leaked quite a bit.

[jsheradin]

Try shorter cables, no USB hubs, different port, etc. for a sanity check first.

Replacing the electrolytics can't hurt but I wouldn't rush to blame them. Double check that the board is getting a healthy amount of power. That behavior sounds like a controller that's browning out. An 8049 is going to have a tough time running on anything below ~4.9V. Measure across the controller power pins and see what it's getting. Is your board one of the AT/PS2 variants or Wyse protocol? Are you using a converter? If it's Pro Micro based, try bridging J1 with a bit of solder.

Give the controller area of the board a very close inspection under good lighting. Look for cracks on any of the solder joints, traces, contamination, etc. If something's suspicious, buzz it out with a multimeter while flexing the PCB in various directions.

Intermittent faults like this are among the hardest to troubleshoot.

[drevyek]

Electrolytic capacitors should always be considered suspect. The fact your board's working fine for a little while, then goes wrong, also points to them. They sound like they're only barely still working, having leaked quite a bit.

That was my suspicion as well. I'll replace them (when I get some) and report back. I assume the ceramics are fine -- they don't look messed with.

Try shorter cables, no USB hubs, different port, etc. for a sanity check first.

Double checked with a logic analyzer, the codes "make sense" but are all over the place.

Replacing the electrolytics can't hurt but I wouldn't rush to blame them. Double check that the board is getting a healthy amount of power. That behavior sounds like a controller that's browning out. An 8049 is going to have a tough time running on anything below ~4.9V. Measure across the controller power pins and see what it's getting. Is your board one of the AT/PS2 variants or Wyse protocol? Are you using a converter? If it's Pro Micro based, try bridging J1 with a bit of solder.

Still happens even when plugged directly into a PS/2 port. Testing the voltage, I'm seeing (with my converter) 4.94V steady. Thankfully it's a PS/2 variant, so converting is no problem.

[drevyek]

Reporting back -- It was the electrolytic capacitors. I didn't check which one of the two it was, but replacing them with brand new equal-value caps has it running directly in a PS/2 port, and (after some fiddling) through my converter.

I've been working on this keyboard now for about 3 years on and off, and to have it be finally working again is a huge catharsis. I went through the full disassembly and cleaning process, running them through an ultrasonic cleaner to clean off the corrosion and grime from the switches. I found interesting that the cherry stabilizers on the board don't match modern stabilizers -- the sliders are smaller and don't have the little feet that people clip off, and the bodies that clip to the plate are slightly different. There is also the mammoth spacebar to go with it, which was rusted to hell and back -- its stabs slide in from the side. Very odd keyboard.

The keys have yellowed to a M0110-style brown, so retrobrite might be my next step. I would love to show off the blue doubleshotting in the caps.

Thanks for the help in narrowing it down!

[Muirium]

Congrats.

Honestly: electrolytic caps are time bombs and always the number one suspect, in my view.

(Despite their similar name: ceramic capacitors are entirely different and no such problem.)

[DMA]

ceramic capacitors are entirely different and no such problem.

Unless they are Soviet-manufactured, of course.

[Muirium]

Very ЩУЅЭ, comrade.