Got a call from a gentleman with a Bally Star Trek. The game was mostly working fine but the player 1 display was missing a digit and there were no GI lamps working in the game.
Upon inspection of the rectifier board, I saw that the GI fuse had literally burned itself off the board. The bottom of the fuse bracket had completely burnt off, likely from being over fused at some point. Proper fuse for the GI circuit in these games is a 20 amp fast blow.
I brought the rectifier/transformer board and Player 1 display back home with me to repair. I replaced the GI fuse clip that came off and put in a new 20 amp fast blow fuse.
Missing digit on test bench:
For the display issue, I checked the common R1, R3, R5, R7, R9, R11 resistors that can easily go out of spec, but they were all fine. I reflowed the header pins across the entire bottom end of the board, and our missing digit reappeared.
Over time these header pins can become stressed and crack or lose continuity to the pins. I took the two items back, installed them and then went through the game to ensure all lamps, switches and solenoids were working properly. Star Trek is back in action!