Several questions, re: TH-5539

[kristian]

This is going to be several questions, be warned.

Got a Tai-Hao TH-5539 with white Alps switches from a former coworker of mine. Reeks and smells of automotive resin/glue (aka "that new car smell"), came off from a PLC controller enclosure of some sort. Bottom cover says it was QC ok'd sometime in 1991.

I was able to convert its original 'fat' DIN connector to PS/2 and use it for a few months and then it started flaking off--status lights would flash, keys will get stuck and spam, ex. "xxxxxxxxxxxxXXXXXXXXXXXXXXXXJJJJJJJJJJJJJJJJJJJJJJJ" or simply freeze altogether. Usually, disconnecting the keyboard, wait for a few seconds and re-plugging it (I am using a powered PS/2 to USB converter) will work for a while, and it happens all over again. Changed the original 1N4148 diodes and the lone 10uF electrolytic cap inside, and somehow got it working for a few days and then it would freeze (status light flash, then hang).

Last night I got so bored, I brought my toolbox out and disassembled the living cock and balls out of that keyboard hoping to find out what could possibly be wrong. Wiped down the board with isopropyl alcohol, checked the PCB for broken traces, bad solder joints and did some basic checks on the board with the multimeter, but still no cigar.

With the keyboard completely disassembled now, I wanna know what are my options now for this baby:

• Keep the Alps switches and keycaps for a possible donor to a new PCB/keyboard kit, like the 66% Clueboard assembly? Can Alps switches be force-fitted to PCBs that use Cherry-style switches?
• Shotgun the components (diodes, resistor, capacitors, the 74LS05 chip) and hopefully it will sort itself out?

As for component failure, has anyone got experience reconditioning old keyboards from the 90's? AFAIK the IBM Model M's will type like drunk once the electrolytic caps have dried out. I am no electrical engineer, so I'm not sure what effects will be caused by failure modes of resistors, diodes or the small ceramic caps marked "25" and "104" (possibly 25 and 104pf values?).

Also, recommend me a PCB that will fit Alps switches--I know Clueboard has some, but want to know if there are other options.

I'll post some pics once I get off work

[kristian]

Bump.

[Sangdrax]

Check if that blue electrolytic you put in is soldered with the right polarity that the old one wasn't a bipolar or anything, that the grounds on the board are connected right and that the chips are seated well and have continuity in their sockets.

If you really want to do the whole board and if you got a cheap component tester, you can just desolder and run all the stuff through it to see if the values match up with the case codes if you want to be 100% sure. That being said, diodes, metal film resistors and non-electrolytic caps last basically forever. I've reconditioned high voltage amps from the 1960's and they just needed a recap and to replace some carbon comp resistors that drifted horribly over the decades.

But if you go through all that trouble, you might just want to go ahead and yank all that stuff then solder a new controller to it and get programmable keys and stuff. Or like you said, harvest the switches for some other project.