Service manual

Wells-Garnder Color Vector Monitor Guide
Page 72 of 73
TESTING YOUR WORK
Test the Game Board Outputs before Turning the Monitor On.
Make sure the game board is outputting correct voltages before you power the monitor
on! Otherwise you can waste the monitor and all the above work. To test the outputs, set
your meter on DC volts and measure the leads of R600 and R700 (fuses) of the deflection
board. These are connected to the plug with wire colors yellow (R600) and orange
(R700). The correct voltage should be in the +0.5 to -0.5 volt range (basically zero volts).
The voltage will fluctuate because of changing deflection signals. If the measured voltage
is between 5 and 15 volts (positive or negative), then check the X and Y amplifiers on the
GAME board. Also check for broken potentiometers on the game board.
Spot Killer On.
If the "spot killer" LED lights on the monitor's deflection board, this indicates there is a
problem. First test the voltages going to the large chassis-mounted transistors (2N3716
and 2N3792). Set your meter on DC volts. With the monitor powered on, put the black
lead on ground (the metal monitor chassis), and put the red lead on the metal case of each
of the chassis-mounted transistors. You should get either +30 or -30 volts DC. If you do
not, there's a good chance one of those chassis-mounted transistors is bad. With the
monitor off, use your meter (set to continuity ohms) and make sure the metal monitor
chassis is not shorted to the metal case of each chassis mounted transistor. If it is, the
mica insulator is probably damaged (and the transistor is probably blown).
Screen Glitters After the Game Warms Up.
The small XY adjustment trim pots on the game boardset are probably at fault. These
trim pots are factory adjusted and sealed with some hot-melt glue. As the board warms
up, the expansion rate of the trim pots and the hot-melt glue is different. The glue can
expand enough to separate and damage the small plastic pots! You can try removing the
glue, but often you will have to replace the small trim pots (10k, 2k, 200 ohms). The only
hard value to find is the 200-ohm pot (the 10k trim pots you can get at Radio Shack). You
can get the 2k and 200-ohm trim pots from Mouser Electronics, or other electronic parts
houses.