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?