When is the last time the power supply was rebuilt?

I know I'll sound like a broken record, but 30 years is longer than most of those electrolytic's are spec'd for. I usually rebuild the supply before I waste time troubleshooting old supplies.

Sounds like the 5 volts is sagging and causing a MPU reset. Sound runs off a different processor so any sound still in progress will complete as the MPU reboots.

Ed at GPE sells a rebuild kit. Search of the forum and a look at the pinwiki for williams system 3-7 will net a ton of information with regard to random MPU resets.

Doesn't sound like socket issues but as always check for and replace any Scanbe sockets or other sockets you can pull the chips from with just your fingers.

Reset circuit uses 12V on these, but 12V and logic 5V both come into the CPU board on 1J2 (top left) from 3J6 on the power supply. If unplugging and replugging these helps then replace the headers (optimally replace the plugs too but sometimes you can get away with just the headers).

If the big capacitor on the power supply has never been replaced then that's a good idea to do regardless. If you are using a System 6 or earlier power supply then the two rectifying diodes should probably also be replaced or upgraded to 6A4 or similar.

My rule of thumb is make sure the power is right first. If not, you'll just be chasing your tail. If the big giant capacitor on the power supply is brown, you need a PS rebuild.

viperrwk

Who carries the big capacitor?, GPE is out

Big Daddy also sells them.

http://www.bigdaddy-enterprises.com/

viperrwk

Looks in stock to me... last two on http://www.greatplainselectronics.com/Category-108.asp

The problem is Ed is out of cap kits to rebuild the PS because he's out of the 100uf 100v caps in the Richey (which he normally puts in the kit) but does have it in the Nichicon. So you can order all the individual components for the kit from him. He's still filling orders but has said it will be a while before he starts putting kits together again.

viperrwk