Here's a follow up image from my first post on this Bally 1978 Playboy machine. I've opened the backbox and the mpu looks like this (mainly corrosion on bottom). The light blinks
MPU089 Williams Pinball Machine WPC89 MPU Board Rottendog – Little Shop Of Games
MPU SETUP INO - Pinball Electronics from barakandl
Ultimate Solenoid Driver Board Pinball Games | AlltekSystems