I am trying to repair a Black Pyramid, and it is showing some unsual and seemingly random behaviour.

Whenever any of the inline drop targets are down, it will either: tilt, jump to next ball, reset or add players. Sometimes this occurs immediately after a drop is dropped, other times its when other switches are hit after they are dropped (normally pops or hole up top). There does not appear to be any consistencty in how long one of the problems occure (ie: immediately or 10-20 seconds after a drop is dropped), nor what problem occurs (can be any of the above listed).

The game still does it with the plug to the coin door removed, so not a short in the coin door area. The problem occured with the original MPU, plus i put a brand new Weebly MPU and it showed the same behaviour - so its a switch or wiring issue, not MPU.

I have narrowed it down to this only occurs when the plug to the swinging motor board is plugged in. At first i thought it must be the switch (the swinging motor board has the moving target switch wires, plus the wires for the motor - so 4 wires - it also has a diode and cap for the switch). I tested the diode in circuit, and it tests fine - i also snipped one leg of the cap - made no difference. So then i left the plug in, but unsoldered the wires going to the board for the switch....the problem remained!!!

So then i removed the 2 black wires that drive the motor - and the problem went away. I could have 3 games, drop all the inline drops and it played perfectly! So then i reconnected the switch wires (but not the motor wires), and it continues to play fine.

So - from this - it seems that whenever the motor wires are connected (regardless if the switch ius connected or not), it plays havoc with the switch matrix somehow and causes random resets (maybe slam tilt), normal tilt, or add players or end the ball.

So the easy solution is to leave the motor disconnected, but the swinging target is a cool feature, plus its annoying me why its happening. Has anyone got any ideas what i can test or repair to try and get this working properly?

Pic of board

PXL_20220701_103246806 (resized).jpg