Star Tech Journal

Rare Willianis Reset Probleni:
Using A Storage 'Scope
Mario Van Cleave
Pinball Doctors
Salinas, California
SUBJECT
It seems I've had more than my share ofWilliams
reset problems in the past few years. The
strangest one of all showed up on an
Earthshaker recently.
PROBLEM
This game was getting complaints of resetting at
random (as they do most of the time). Upon
pulling this game from it's location the usual
check out procedure followed.
~. Using a Digital Volt Meter I found initially 11.9
Volts at test pin 3. I've had these pins run at this
voltage but have discovered they run better
above 12 Volts.
I moved on to other parts of the circuit only to
discover less than 5 Volts at test pin 1 which is
generally not a good indication. After removing
C 10 and testing it out of circuit it was replaced.
Power up showed no change.
SOLUTION
I grabbed the storage scope and went to work.
After several picture taking episodes, I discov-
ered occasionally a missing half wave! The
problem was the bridge rectifier BRI. The ma-
chine only has 2 amps AC loaded on this rectifier
and its rated at 35 amps (heat sink rating).
CUSTOMER SERVICE
A conversation with Tom Cahill, Customer Ser-
vice Manager at Williams Electronics, left me
assured this is a rare occurrence.
Guys, for the ultra tough problems, use your
storage 'scope or get one.
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