I have an Allied Leisure game with an early PCB50210125E MPU. I've removed the resistors for the warming circuit and added diodes on all the switch input lines.
When incandescent bulbs are installed, the feature lamps work fine.
With LED bulbs installed, whenever I activate a switch or whenever a coil fires (kickers, pop bumpers, chime coils), lamps that are not supposed to be lit flicker in concert with each activation.
With an LED feature lamp that is supposed to be lit, it stays lit and does not experience flicker or strobing.
I noticed that on the schematics for newer versions of the MPU, there were .1uf capacitors added to each switch line and tied to ground. However, since the LEDs are flickering when both switches and coils activate, I'm not sure that this would be the solution.
What might be the best approach to address the flicker? Add a .1uf (or .22uf or some other value?) cap across each lamp socket to act as a surge suppressor?