Location: Centennial (Denver), Colorado.
Symptoms: Blows fuse on power up.

When powering up the machine, the F114 fuse (8 amp) would blow.  This fuse powers the lamp matrix as well as the CPU +12 volt circuit through a downstream fuse (F115), which is used for the switch matrix.  So when I first power up the machine, the CPU was booting but none of the lights were flashing and the switches on the coin door were unresponsive.

I disconnected all of the lamp matrix connectors from the Power Driver Board (J133 through J138) and powered up the machine, and the fuse blew again. Since all of the connectors were disconnected and fuse F115 wasn’t blowing, the problem had to be in the power supply itself.  There are only two possibilities, a shorted bridge rectifier or a shorted capacitor (rare).  I check the bridge rectifier and it was shorted between “AC” and “+”.  I had a spare bridge rectifier on hand and replaced it.

The machine powered up as normal this time.  A lot of the matrix lamps weren’t working.  I replaced a bulb near the flippers and it still didn’t work.  I thought maybe a row or column driver had failed.  So I ran the test for individual lamps and marked a copy of the matrix with an “X” if the lamp wasn’t working.  No clear pattern emerged to indicate a row or column problem.

So I started at the first bulb in the test and looked at each one.  It turned out that most were burned out.  Also, I found a broken wire for Row 1 of the matrix.  Reconnecting that got about 6 more lights working, including the first bulb I had replaced where replacing it didn’t help.  It’s a tedious process, but in the end the machine looked and played well. I probably replaced two-dozen bulbs.