I've been working on this Flash Gordon and have rebuilt the solenoid/driver board. The game boots fine including the sound board. When a game is started and the first ball is played, it seems when a target, not always the same target or switch is made, the knocker fires. Subsequent balls play normally. Only the first ball has the knocker problem.

All voltages including the 5VDC are stable.

The MPU has been replaced with an old version of a Weebly MPU. (was in the machine when I acquired it ) The connectors have been checked and I find no problems. This MPU doesn't not have the switchable game applications.

Solenoid test works every time without any problems. All solenoids fire without any cross firing.

All playfield switch caps have been cut away -- unless I missed one. I haven't done a switch test only switch testing in game mode.

This is a nice clean machine with no evidence of excess moisture or other abuse. Way better than average condition.

I wonder if there is memory corruption in the MPU. I believe I have to burn a chip or two to clear the memory per nvram.weebly web site.

Good point! I'll check. Thanks..

Solved. Indeed it was the replay settings that were all zeros. Thanks! (I did waste a lot time troubleshooting before posting)