Service manual

Wells-Garnder Color Vector Monitor Guide
Page 51 of 73
2 - POWER SUPPLY CIRCUIT
The Low Voltage Power Supply is to be bypassed in this modification. The input stages of the
deflection circuits used in this monitor are of the differential type and exhibit a high common
mode rejection. This characteristic will filter out any noise or ripple of the power supply.
A. Cut diodes D104 and D105 out of the power supply circuit (Schematic 2.1)
B. Cut the wires at P100 leaving about two inches at the plug.
C. Make a Rat Tail splice connecting the leads at pins 1 and 4; also, splice the leads at
pins 5 and 7. [Note that pin 2 is missing from the plug.]
D. Solder and cover the exposed wire with electrical tape or shrink tubing.
E. Cut the remaining wires flush with the plug (leads at pins 3 and 6).
[Alternatively, you could make a non-destructive modification by using a 7-position molex (or
comparable) plug and making a wire loop between pins 1 and 4, and 5 and 7. Never a very good
idea to cut up your original harness! An interesting benefit of this modification is that it removes
two chassis transistors (Q102 and Q103) from the monitor. Please refer to Schematic 2.1]
NOTE: This [Low Voltage Power Supply] modification will require readjustment of the monitor
color, focus and signal level from the logic board. This is due to the higher supply voltage now
available at the deflection and color stages. This modification will remove about 45 watts of
power from the bottom plate of the monitor chassis and cause a noticeable reduction in
temperature.
[notes from Zonn:
* Though it claims otherwise, removing the regulator from the low voltage side make for
irritating jitters and blooming on the vectors. This might not be so bad from an
"operators" point of view, but as a collector is was unacceptable.
* Removing the regulator increases the voltage across the output yoke drivers. This might
have an advantage of a slight increase of vector speeds when moving large distances,
but it also means the transistors must dissipate more heat during large movements.
Since Tempest was written for the monitor as it was designed, the speed increase is
meaningless, but the heat dissipation is critical!
* The low voltage regulator designed by Atari really sucked, I came up with a re-design
that was slightly more complicated than the LV2000 -- I switched to the LV2000. The
best thing to do with the low voltage section is to install an LV2000.]