Sounds like an issue in the original mpu,(spider chips), suggest NiWumph.

System 1 games use BCD coding of display digits, and can only display numbers 0 to 9, while the 4-bit BCD can hold values 0 to 15. If game memory is corrupted (lost battery power) it can contain invalid numbers that show as garbage.

To clear the problem with erratic high scores, you need to reset the highest score. Repeatedly push the test button on front door, until "10" is shown on credit display, then push the reset button on CPU board. This resets the high score, You can set new score by keeping the start button pushed down. Store the new high score by pushing the test button once more.

Do the same for all three replay levels (test steps 7, 8 and 9). Remember to push the test button after setting the desired score, otherwise it will not be stored.

Did you ever resolve this issue? I know this is an old thread, but I'm experiencing the exact same thing with a Totem. Displays either work fine, come up with all 000000 or don't work at all. There seems to be no pattern to it. Display connectors on the MPU have been repinned and the edge connector is clean.

I would check the 60V for the displays coming from the power supply.
Resolder the connector A2P3 and check resistance of R33(have to be 33Ohm) on the PS
If this voltage goes under a specific limit the displays will just go off.

Not much information to go on, but since it affects all displays and sometimes zeros/blank, that probably has nothing to do with the displays themselves, or even the display section of the MPU. Sounds more like a booting issue. What's the history and condition of the MPU?

I agree with you. I think it has something to do with the amount of time the board's CPU is held low upon bootup. The board is in excellent condition. The original battery has been removed. No corrosion. Ground mods have been done. Voltages from the rebuilt power supply are perfect at the displays.

Game worked great until the outhole solenoid locked on. Z6 was fried along with the associated transistor. Not sure which part took out which, but both were found to be bad. I replaced the bad parts and the coil (the game was left on long enough to destroy the coil and blow the fuse). Now the game works fine but the displays have this issue, which was not present before. Again, they work fine maybe every 4th or 5th time the game is powered on.

What's the easy way to increase the number of milliseconds the reset signal is held low? I remember reading about this before but can't remember which component to replace. It seems this would be the easiest way to test if that's the problem.

Thanks in advance for any help.

I don't think I can be much help, but that certainly seems to point to the reset/boot section of the MPU, IMO.

https://www.pinwiki.com/wiki/index.php/Gottlieb_System_1#MPU_Boot_Issues