I had a swemmer 80B mpu a few years ago that wouldn't boot. I found that if I pulled the nvram out it booted fine making me think the nvram was bad. Swapping nvrams didn't help. I ended up having fred repair it and he found a bad surface mount transistor in that area of the board. Granted this was like 4 or so years ago and could have been an isolated thing with just my board but I'm just throwing this out there if it helps someone. Try contacting fred he has always been helpful with questions and repairs.