I’ve been trying to diagnose a hanging IIGS.
After 30mins of play, my IIGS hangs. The screen freezes and a ctrl-Apple-reset goes to a black screen, no boot sound. It never drops to monitor like I think a random crash should do. When I power off and on, the screen shows colored checker board. After sitting off for 10-15 minutes it works again. This is with the chassis closed, and display on top, e.g. hottest config.
With monitor on the side, and chassis open, it never hangs, it has to be an overheating problem. My first thought is PSU.
I reproduced the hang, then immediately opened the chassis to test voltages. I left it on and underload to get a good measurement. Everything looks ok. -5v was a little high at -5.20v, and comes back down to -5.12v after cooling off. Is this enough to crash a iigs? Is it really the PSU?
I also used an oscilloscope to test for noisey DC, but it looks clean.
Any other ideas? All the bus slots are empty. Only card in the machine is a GGlabs 8MB expansion in the memory expansion slot. Next thing I’m going to try is pulling the memory expansion, or running a memory test.