Star Tech Journal

December 1 997
STAR*TECH JOURNAL
Conuck
Corner
"Just the Facts~ eh?,,
John Liikala
• Canadian Amusements • Burnaby, BC • Canada
WEL15 GARDNER
WEL15 GARDNER
WEL15 GARDNER
U3000 HIGH
U2000WEAK
U2000/5000
VOLT SHUTDOWN
VIDEO
FIRE PREVENTION
REPORTED PROBLEM
REPORTED PROBLEM
I have a U3000 WG Mod
14K3002 that keeps going into
high voltage shutdown. If I ad-
just the HV pot just a little tne
unit will run fine. I have changed
the hor. output transistor but still
have the same problem. All volt-
ages are within specs. Any help
will be apreceated. Thank You.
I am having a problem with a
Wells Gardner monitor which I
have never seen before. With all
the screen controls set to their
maximum, the picture is just
barely visible. All B+ and asso-
dated voltages are within normal
specifications.
ADVICE
Did you check your A/C voltage
off the isolation transformer?
If its more than 123VAC, it will
cause that problem. I've had a
bunch of isolation transformers
"step up" the A/C voltage in
some older video games.
This issue, answers to
questions posted on STJ's
online tech exchange
center (Star Tech Journal
Message Board on the
World Wide Web). This
service can be found at:
www.StarTechJournal.com
I have tried to contact Wells
Gardner concerning this prob-
lem but I only get their answer-
ing machine in the tech dept. and
they never call me back. Any and
all help would be appreciated.
Thanks
REPORTED CoNDmON
In the IC power regulator circuit
for U-701, the zener diode Z-705,
9.1 v 1/2 watt, may short out.
Even when the deflection circuits
have stopped running, the
switching regulator circuit con tin-
ues to deliver the B+ until com-
ponents heat up enough to either
burn themselves open, or burn a
dime-to-quarter sized hole in
your PCB!
ADVICE
I have seen this this problem
many times and I wonder myself
if there is not a better solution to
this circuit failing all the time.
ADVICE
This is a simple problem. Either
your voltage that supplies the
colour processor is low or the
chip itself is bad.
To isolate this problem try
swaping the neck board with an-
other U2000 or US000 which has
the same neck board. These are
usual problems of faded video in
a new U2000 . The other extreme
is maybe your tube is shorted at
the colour guns .
Here are some solutions you can
use to better this circuit:
• Check to make sure R760 is a
4 70 ohms 2 watt flame proof re-
sistor. • Change RIOS to 5 watts
ceramic resistor 470 ohms. • Z705
to 10 volts 1/2 watts. • Q703 and
Q708 to 2SC2610 or ECG399.
Next• Z702 to a 1N4742A zenier.
• C712 to 220 25 volt capacitor.
This will improve the circuit to
some extent, but use this mod at
your own risk.
.
t