So now that I have a proper working bench power supply, I'm able to see what this DE MPU is doing wrong.

With a game rom in socket, +5v on, PIA on-off quick, Blanking on, then blanking drops out after about 3 seconds.

With Leon's test rom in socket, on boot, I get about 2-3 relay clicks of the PIAs doing there thing, then crash, but sometimes more or less.... IRQ drops low about 3 seconds after the last click.

With no rom in socket, 2 volts on all address lines for about 3 seconds, then they all go high.

Identical behavior with another known working CPU.

Address line short? Chip selection? PIA?

I've swapped RAM with ramtron 1608. I also buzzed this board out about 3 times prior, so good there.

I was just curious if this partial working behavior was typical of one section, like bad 74ls244s, 245, chip selection ICs. I've repaired a similar issues, but they were less complicated to debug because they were obvious to spot.

i replaced the cpu socket and it is more consistent now, but still hangs...Replacing ROM and RAM sockets now.

Got Leon's test running. Isolated it down to the display PIA @ 11B. The LED pin at pin 6 there was randomly firing, and pins 2-5 are completely dead on it. Could be more involved, but starting here as it is the most likely cause since the decoder & led lines are isolated.

I got lucky this time and it was just a bad RAM socket, which has been the case historically for me with any intermittent issues like this (bad sockets). Thanks for the input.