I'm getting my games ready for our annual Halloween party and naturally that's when the Knight decides to stop playing nice. I turned the game on (I'll admit it hasn't been on in a month or 2) and no feature lights + garbled displays. The game has worked fine for the most part for years, i had the boards serviced by the coin up cauldron a long while back and have had only a few problems ever since. I've had to replace the 555 chip (and replaced the nearby cap and transistor for the blanking circuit as well) twice in the past few years to deal with a blanking problem--just mentioning that in case it could be related. Otherwise i haven't really had to do much other work on the boards to date. I have replaced both backbox-mounted bridges in the past couple years (and have added fuses for them, as everyone should!!)...

All it does now is the general illumination comes on, and the mpu displays "0" and the 2 LEDs next to the digit stay lit. No feature lights, no displays. I've unplugged the coil connectors to save fuses etc from possible weirdness from the mpu in the meantime.

I have to start pulling fuses and testing voltages etc, but figured I'd chime in here before i get too far ahead of myself. Any suggestions where to start looking?

Tested +5 and +12 at mpu:
4.93vdc
12.4vdc

Tested for dc volts at blanking test point (should have tested at pin 40 as you recommended)--got 0vdc.

Pressed on socketed chips, and re-seated connectors around mpu, suddenly started getting ~3.7vdc at the blanking test point after booting up.

Game now boots into attract mode, can play a game, etc.

If/when problem returns, I'll try pulling the mpu and driver apart and reseating them, and I'll re-seat any socketed chips as well.

Actually--now that I've had the game in attract mode for a bit, I'm noticing the Ones digit on displays 1, 3 and the credit/match display is flickering on and off and are sometimes garbled--any suggestions where i should start looking for the culprit?

Edit: reseating all connectors to master display board and display connectors on mpu cleared up digit issue.