Compact XVI woes

[DejahThoris]

I have two Compacts.

One is fully working.

The other gives a black screen but will show the generic error upon interrupt.  The drive gives a quick hum on start-up but it doesn't attempt to boot from a disk. The lighted key directly above CLR on a compact keyboard blinks on and off every few seconds.

I've tried Opt1, Opt2, and CLR on boot up as other threads have suggested.

The system is completely recapped. New battery. Can't find any corrosion or cut traces. 

I'm using the same pico that works on the other Compact as my power source. I've swapped in known working floppies, known working keyboard PCB, SCSI PCB.

I've tested every ribbon cable for continuity end to end and I have no breaks.

I've touched up every solder joint that's looked off.

And I'm out of ideas.

Help!

[leonk]

This is a compact.  It uses SMD capacitors on the main PCB.  Unlike the full size computers where the power supply will die, here it's the exact opposite - the PSU is good but MB will die.

I have restored 4 of them.  1 of them I could not bring back to life.  The damage is under one of the IC's.  Only fix is to practically remove the IC.. clean, and solder down.  Not practical.  I can remove 160 pin QFP .. but I don't have 100 hours to work on a single computer and nor should anyone go to that extend.