5150 16k-64k Keyboard not working?

[modem7]

Fortunately, the keyboard "controller" on the 5150 is very, very simple--mostly just a shift register. (See the schematic) using commodity parts.

I have extracted the keyboard related circuitry, and put that at [here].

[modem7]

With multiple symptoms, I sometimes just pick one symptom and run with that.
If the fix for that symptom fixes the other symptom/s, good.
If not, pick one of the remaining symptoms then run with that, etc.

Pin 1 was suppose to have +2.0v to +5.5V I shows .1mV or 0

With no keyboard attached, at POST end (a normally running POST), pin 1 of the DIN connector should be HIGH (pulled HIGH by RN1, with U80 not driving it LOW).
Working backwards in the circuitry, what do you measure on pins 11 and 13 of chip U80 ?
Both pins are expected to be HIGH.

[maxtherabbit]

If you say "also no sound" and clock pin with no signal, that points to a 8284 (U11) clock generator failure (that generates peripheral clock PCLK signal) or maybe 8255 peripheral controller (U36) because both things depend on that. Maybe a broken trace or something shorting pin 2 of the 8284. That should always output a 2.385MHz clock, and goes to pin 9 of U26, is divided by two and goes to pin 9 of 8253 (U34) for the sound and pin 3 of U82 for the keyboard. I would check all that signals and components.

This. If you have a scope check PCLK

[framer]

WOW! I guess I got homework to do next week. I will check the above and get back when I've gotten into it. Family stuff this weekend, wife got plans...


Logic probe, multi-meter and this forum my only tools.

Thanks for the insight for this issue.

framer

[framer]

Confession: Before I read all the replies, I'd given up and pulled all the chips from the board that might be used to fix other PC XT I have. After reading the replies I decided to try again. I re-installed the CPU, memory, ROM basic & Bios. Hook everything backup outside the case so I might do some probing; however, the computer booted right up and worked. I installed it back in the case and ran diagnostics several times perfectly.

So if something does work beat it with a hammer and try again

I guessing a corroded bin must have caused the issue?

Thank all, for keeping me from giving up too early on this system.

framer

[Chuck(G)]

Either that or you have a bad solder connection/cracked trace on the motherboard that's intermittent.

[framer]

I hear that. It might not be over, finger crossed.