I am working on a 1983 vintage Gottlieb Haunted House Pinball Machine for a friend. I have never worked on a PB machine previously, but have considerable electrical/electronics troubleshooting experience. I'd appreciate help from anyone on this forum who is knowledgeable and willing to offer me advice.
At this point, I have determined that the F4 glass fuse (8A slow-blow) pops whenever one of the main playfield solenoids attempts to fire. (No other fuses get blown). With the F4 fuse replaced, on startup, the game appears to boot up properly and after a few seconds the "spooky music" and flashing lights (attract mode?) seem to indicate it is working properly. When coins are inserted and the credit button is pressed, the pinball is released to the launcher and the associated "knock" can clearly be heard. But once the ball is launched into play, the sound stops, and none of the flippers, targets, or bumpers work. Shutting off power and performing examination of F4 fuse shows that it is blown open again.
Per the schematic, fuse F4 appears to feed two bridge rectifiers which are working correctly and supplying unregulated 24VDC and 33VDC. To troubleshoot and attempt to isolate the problem to either the sound system or the solenoids, I disconnected the sound and sound PSU boards and the fuse still blew when the ball entered the playfield. Since it did not appear to be sound board related, I then looked more closely at the A2 Power Supply board and took voltage measurements on all the clearly marked Test Points (TPs). All seemed to be within expected minor variation from the nominal voltages, except for TP2 which is marked 42V, but is clearly measuring 60V. This 42V output appears to be shorted to the 60V (even after disconnecting the J3 connector) and zener diode CR6 has no voltage drop (18V is expected per the schematic to generate the 42V from the 60V). I have a replacement 18V, 1W zener diode (1N4746A) on order and plan to replace it when it arrives. That said, can someone help me in advance to understand where the 42V goes and how it is consumed by this PB machine?
PS I did find the manual on the Internet and so have the schematic, but can't seem to find where the 42V goes in that 50+ page document. Looking at he wiring harnesses, it looks like it goes to the main playfield, but how is it used? Does it somehow drive the solenoids and would the 60V there cause the overcurrent situation that is popping fuse F4? Or am I chasing a phantom here and the root issue is somewhere else? Thanks in advance to anyone who can help me understand the purpose of the 42V supply and also help me to understand if it could be the cause for the bumpers/solenoids/etc. consuming too much current and blowing the F4 8A fuse.