So, a friend of mine had an interesting problem, he purchased a brand new pin that obviously tested and worked well before it was shipped to him, but as soon as he plugged into a GFCI socket in his garage, it tripped the GFCI outlet.
They came and got the game, treated it again, said it worked and played fine, and then returned it. Same problem. What we later figured out was that they did not test it with a GFCI/DFCI outlet.
I am seeing something across multiple classic Bally pins that makes me think it is an actual bug in the firmware. It has to do with the LATCH signals for the displays. Specifically the Credit/Match/Ball (CMB) display.
So I have a stand-alone Mata Hari headboard that is used for testing purposes.
I previously had a AlltekUltimate Solenoid Driver Board (USDB) in it that was powering an Alltek MPU board. That USDB was pulled because it was needed for another purpose and I later received a new USDB as a replacement. However, after connecting this one up it only lit up its +43 VDC LED. (Actually, it also lit up its 180 VDC LED, but that has nothing to do with this post.)