Beside of this, one of my ANS seems to have a broken mother board. Power up by keyboard and front switch is working. But no start chime and no status messages on the LCD. Capacitors replaced. RAM,ROM,CACHE changed with parts from working one. Any ideas what I might could check further?
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Sorry for the late reply. I haven't been checking back here in a while. Too busy.
I repaired an ANS logic board many years ago, and the problem it had was a bad inverter. Just a logic inverter. It was probably a dual or quad inverter because it was in an SOIC or similar package. Not just a little 5 pin thing.
It's between the Clock signal that comes from the CPU card and the clock buffer chip which is on the logic board. I'm sorry I'm not more specific. I might be able to find it, or the region if I had an ANS in front of me. I did this repair about 20 years ago or maybe more.
I don't know if that's a common failure mode, but it fits the symptoms you're seeing.
AFAICT, this inverter just cleans up the clock wave form before it hits the clock buffer, which splits the clock signal off to all the components that need it. It can't be there for timing, because everything takes its clock from the downstream buffer, so everything is adjusted the same amount by the buffer. Even the CPU gets it's signal from the logic board buffer. The raw clock comes off the CPU card, goes through the inverter, gets split by the clock buffer, and then comes back to the CPU card as well as out to the logic board components.
Also, do you have another CPU card to try? Have you cleaned the CPU heat sink grease and replaced the heat sink compound with new stuff? The original has almost certainly turned to chalk by now.