OP

Quoted from TheWiz:

I have a cpu board out of a Star Trek the Next Generation. I have been repairing it on the bench. There was slight corrosion which has been cleaned up and I have installed NVRAM. The board was then put in the game and ran okay for awhile and then starting resetting. I have the board on the bench again and can re-create the failure, which does not appear to be a normal reset. On power up D21 comes on and stays on solid (+5v), D20 is off (diag), and D19 is on (blanking). After about 3 seconds D19 goes out and D20 begins pulsing, which says the board has booted and is running. Then about every minute, D20 goes out and D19 comes on and remains this way for about 3 seconds and then goes back to the way was, like it has rebooted. But checking various pins on the board, the cpu never rebooted, pin 40 stayed high. Pin 1 of U10 stays high, which is the 5v monitor. Address and data lines are still active from the cpu chip. What happens is pin 34 on the ASIC goes from pulsing to low (blanking signal) and pin 35 of the ASIC (DLED) goes from pulsing to high. Pin 80 of the ASIC (RESET) stays high.
Power is good coming in at 5.09 using a KAHR adaptor. 68B09 cpu chip has been replaced with a known good processor, both NVRAM (FM16W08) and normal RAM do the same thing, different EPROM has been programmed and installed. ASIC has been removed, inspected and re-installed. Jumpers W4 and W7 in, W3 removed and 1.5k resistor in for R93. So far nothing has made any difference.
Any ideas?