I would like to disagree here Using the power supply frame as a common point for GND introduces a new potential problem. What's the case......The power supply frame is only isolated from the incoming +12V at the case of the power transistor. This piece of material can be damaged after dismantling the power supply and the result can be +12V at the frame of the power supply. Normally this doesn't hurt but fuses don't like attaching a Ground wire now I did see this happening a few times already. The same counts for using the sys80B heatsink as a common point for GND.

As a common point for Grounding, I always use one of the yellow straps in later system 80A games, the lower hinge of the lamp panel in earlier sys80 games (circuitboards mounted at the lamp panel), or the screw left below in the backbox which holds the panel at which the circuitboards are mounted (Haunted House and later).

Just my 2 cents.....

Greetings from a technician from Holland

Marco

Hello Clay, I've seen it 2 times in 12 years I repair games. At 1 game, somebody left the mica insulator completely, and in another game, a tiny piece of metal became between the power transistor and heatsink which pierced the mica insulator. Well, if the insulator is okay there won't be any problems, but the heatsink is very very close to the incoming +12V which prevents me from using it as a common point for grounding..... Maybe it is a matter of taste or feeling but I prefer to take a different approach.

Marco