Quoted from Quench:Yes it's usually a bad diode CR3. The last MPU LED flash is reliant on the solenoid voltage rippling to zero volts (known as zero crossing detection). When diode CR3 short circuits, capacitor C17 on the sound board prevents the ripple to zero volts so the last MPU board test fails.
Similar issue two weeks ago:
https://pinside.com/pinball/forum/topic/harlem-won-t-boot-with-soundboard-connected#post-6226279
Came to post this ^^^ 99% chance the diode is bad (shorted). Pretty common problem even though less than a quarter amp constant current goes through that diode. Maybe a little surge at power up, but the cap is only 100uF.
Pipe Creek, TX
