Service manual

Wells-Garnder Color Vector Monitor Guide
Page 13 of 73
DIAGNOSING YOUR WELLS-GARDNER MONITOR
All the documentation and boards for the Wells-Gardner 6100 monitors refer to "X" as the longer
axis and "Y" as the shorter axis, independent of how the monitor is oriented in your game.
Confusion arises because the game PCB will refer to "X" as the axis parallel to the floor and "Y"
as the axis perpendicular to the floor and this is dependent on how your monitor is oriented. Why
is this important to distinguish? Well if you notice that there is a horizontal line on your Tempest
screen and you go to figure out why you are not getting any "Y" deflection, you must check the
"Y" portions of the vector generator circuitry on your game PCB but you need to check the "X"
portions of your monitor deflection board!
If your monitor is not working, the very first thing you should do is check all the fuses in the
machine with a meter. There are four on the deflection board and most Atari machines have
seven more in the power supply at the bottom of the machine (six in a fuse block on the left, and
one under a black cap on the right). Remember to check resistance on the fuse HOLDER not on
the fuse itself. Many times a fuse will meter out OK but it is not making good contact with the
fuse holder so it is not conducting. If you always put your probes on the fuse holder, a bad
contact will never trick you. Many times fuses that are not conducting can be made to do so
merely by reseating them after pinching the fuse holder clips tighter. Sometimes the clips are
corroded and need to be cleaned first. The wire contacts connecting to the fuse holders may also
not be conducting properly so you may want to move your leads and test there to cover all your
bases. This rule applies to fuses in general anywhere you find them.
Before you begin work on your monitor, you must discharge the CRT - even if you are just going
to be unplugging the socket from the neck of the CRT (i.e., to gain access to another part). A
tube that has some air in it can deliver a nasty shock back out of the neck pins. It is extremely
inadvisable to work on the HV section while the machine is turned on or even plugged in;
always unplug the game before you work on the HV section.
I would recommend using a High Voltage Probe to discharge the monitor. This is the safest
method, as the probe is designed to withstand extremely high voltages (hence the name, right?).
Lacking an HV probe, you can use this tried and true method, be it a little more dangerous. Use a
plastic handled screwdriver; connect one end of a wire with an alligator clip at each end to
chassis ground and the other end to the metal shaft of the screwdriver. Be certain you have a 1
Meg ohm resistor somewhere in your connection. Using ONE HAND ONLY (put the other in
your pocket) and touching ONLY the plastic handle of the screwdriver (DO NOT TOUCH THE
METAL SHAFT) work the end of the screwdriver under the big suction cup on the top of the
tube until you hit metal. Be prepared for a fairly loud pop and a flash. The longer the monitor has
been turned off, the smaller the pop and dimmer the flash. But BE CAREFUL, picture tubes will
hold a very healthy charge for at least a week if not longer. Even after you’ve discharged it once,
it may still carry a residual charge. It’s better to be too careful than dead, which is why electronic
equipment always carries stickers referring servicing to qualified personnel. Handle the side with
the viewing screen against your chest when changing it. ALWAYS wear safety goggles when
handling the picture tube.