Wells Gardner 19-Inch Model 19K4914
Matt J. McCullar
Forum Fair Arcade
Arlington, Texas
PROBLEM
Last year at Six Flags Over Texas, one of our
Gauntlet machines baffled us with a very
strange problem. When the game sat inside an
arcade there was sound but no picture. I
checked the fuses and B+ voltage, and both were
okay.
After borrowing another department's truck, we
brought it back to the shop. We turned it on and
the picture appeared nice and clear, as if it had
never been gone. First suspicions included a
lose socket, so we checked it over and gave the
game a pretty healthy jarring around. The pic-
ture stayed rock-solid. We even let it run for a
day in the shop and found nothing wrong. So,
like dummies, we trucked it back into an arcade.
Keep in mind that the only time games can be
moved around at S.F.O.T. during the season is
after two in the morning. We all had worked very
hard that day and putting this Gauntlet game
back into one of the arcades in the park was all
that stood between us and going home.
Since it worked fine in the shop, we drove
around, set it down, plugged it in... and rolled
our eyes when the sound came on but the
picture tube stayed dark! We roughhoused it a
bit, but it didn't help. Back on the truck for a trip
back to the repair shop.
Toe next day I plugged in the game. We are in the
shop now, and you've guessed correctly: the
blasted things works in here! We checked it over
again, beat the holy daylights out of it in hopes
of causing it to screw up, and the picture never
wavered once. So we trucked it back out into the
park again that night.
Guess what happened.
By this time Gauntlet, a pretty massive game,
enjoyed a free ride into and out of the park three
times at ungodly hours. Each time it behaved
like new in the shop, but shut off in the arcades.
Other Gauntlets in the arcades worked fine, but
not this one.
Finally I decided to let the machine have its fun
and run in the shop until it gave up and shut off.
Sure enough, the picture blinked out after 24
hours.
SYMPTOMS
One clue to work with: every time there was no
picture, there would be no high voltage and the
heaterwouldn'tlightup. Both thesevoltagesare
driven from the high-voltage transformer,
whose primary connects to a chassis-mounted
transistor, Q352.
The location of this part is shown in Figure 1.
The B+ voltage was still fine, and the oscillo-
scope proved the video signals were reaching the
monitor.
As you can see in Figure 2, an oscillator circuit
uses Q352 to drive the high-voltage trans-
former. Sticking the 'scope probe on R364, an
oscillating signal was definitely present: but
when I touched the probe to the base lead of the
transistor's mounting socket, the screen sud-
denly lit up! The heater came on, and the high
voltage brought a nice, sharp picture to the
screen.
But the instant I removed the probe, everything
downstream shut off. Aha! I touched and re-
moved the probe several times, and the screen
responded simultaneously.