Chandler, Arizona
One of the 7 amp 12 V unregulated (and thus 5V logic) fuses was
blowing on GNR which was disabling the entire game. No CPU, no sound
board, no display . It would take a few seconds as you could see it
warm up, warp and them blow.
I checked the bridge and it tested OK. Other usual culprits include
the voltage regulator and caps. To check all of these I plugged in
only the transformer plug and removed all other plugs from the power
supply.
Fuse was OK, one at a time I plugged in the CPU, sound board and
display supplies (some of these were disconnected at the respective
boards). And none of them caused the fuse to blow.
Lastly I reconnected the 5 pin (4 wire) connector under the GI wire
connector. this was the culprit. WHAT THE HECK IS THIS ONE FOR??
OK 2 of the wires are the GI relay as they have always been but what
are the other 2. Went through a quick check and the only other thing
not working in the game was the GI for the slings and inlane guides.
All 4 of the regular GI circuits were working so this set of GI
strings must come from the other 2 wires. Checking these sockets I
found a shorted lamp socket (2 actually) under the left slingshot.
What an unfortunate design decision. Instead of stealing 8 lamps from
one of the GI circuits used for the translite (there must be 30 plus
bulbs behind it) they took the 12 volt unregulated AC (which becomes
the 5V logic) and half wave rectified it into 6V for an extra GI
circuit, so now a single bad GI lamp socket can disable the entire
game.