Got three WPC-89 MPU boards sitting around that I can't fix. They all have different symptoms with the diagnostic lights. One seems to boot, then reset, constantly. One blinks twice, and one blinks once. I've replaced the main ASICs with brand new ones on all of them, so I know that's not the issue. The double blink one I've replaced the RAM chip, with what I think is an acceptable substitute, and still get a double blink. I guess I'm looking for a place to start with these. I've reached the level of my own knowledge. I see pinball rehab has a wpc mpu testing page, but it doesn't really tell me where to start from these diagnostic flashes. Can anyone walk me through things I can do without a scope or logic probe?

You know, I never even considered the two varieties of RAM. Will have to look at it. As for the resetting one, how does one jumper the watchdog at J203? It's doing this on the bench, with a solid 5 volt power supply, and a good supply at the processor and PROM.

Edit: Just checked, and it's jumpered correctly for the RAM in it. I guess I'm curious as to what it's testing and then failing to make two flashes. Would help me narrow things down a bit.