The latest one I’ve been trying to fix is a PB180 daughtercard - it is unstable (locks up after a few minutes doing a RAM test) with a RAM expansion card above 6MB installed. I’ve found out that if I blow a fan over the CPU card it remains completely stable, or equally if I use a RAM card with buffers onboard. I’ve poked and prodded it a lot and it’s not clear what the problem is. It’s an earlier revision PCB and I’ve noticed that some of these have a bodge wire from an inductor to a buffer chip fitted at the factory. Apparently it’s to provide a cleaner (less noisy) 5V feed. Mine doesn’t have this bodge - I tried replicating it but it makes no difference.
I also have two faulty lower logic boards - #1 powers on intermittently and the sound comes and goes. It also fails to boot completely if I try to plug in an external monitor. #2 Starts up consistently but randomly decides that ADB, sound and floppy won’t work.
In theory I could use parts from board 2 to fix board 1 if I can figure out what’s gone wrong. Being intermittent though it’s really tricky to pinpoint.
