Service manual

Wells-Garnder Color Vector Monitor Guide
Page 21 of 73
Symptom: Spot Killer ON and display dead
Check the fuses first. If they are OK, then check the six transistors mounted on the chassis as
described earlier. If you find at least two of the deflection transistors or one of the power
transistors bad, then that is definitely tripping the spot killer. A good trick to figure out where the
problem exists is to turn your brightness up all the way and see what your picture looks like. The
spot killer does not turn the Z signal all the way off so if you turn the brightness all the way up,
you should be able to see a very faint picture. Based on what the picture looks like, you can
decide which half of the circuit is causing the problem (either the X or Y portion). If you know it
is a problem on your deflection board (i.e., swapping in another board makes the monitor work)
then check R808 (X) and R809 (Y) to make sure they are not open. These resistors allow current
to flow to the spot killer circuitry and if they open then the spot killer thinks something has
happened to the amplifier circuitry so it kicks on. You can tell if this is your problem by turning
the brightness up all the way; if you see a complete picture, then this may be your problem. If all
this is OK then you probably have a game board problem, particularly if you are unable to "play"
the game (see the credit lights blink after you punch up credits and hear the game sounds after
you push start).
Symptom: Display dead after a Cap Kit
Cap kit installed but still no picture (spot killer may or may not light).
The problem is most likely Q603. Occasionally you will see Q603 (Q703), or Q604 (Q704) go
bad. If one of the transistors does die, be sure to check the resistors and diodes around it,
particularly R611 (R711), R612 (R712), and D602 (D702). A common modern day replacement
for MPSU57 (Q603/Q703) is NTE189 and the part for MPSU07 (Q604/Q704) is NTE188. These
should be greased where they touch the heat sink (like the chassis transistors) to improve heat
dissipation. If you are having trouble with these failing, you might want to beef them up by using
TO-202 package upgrades to NTE50 (MPSU57) and NTE49 (MPSU07).
Symptom: No X (or Y) deflection
I have seen two deflection boards like this. On one, the problem was that R710 (R610 for Y) was
open. How you fry a 10-Watt resistor and nothing else in the circuit is beyond me; perhaps the
PCB was dropped and it landed on R710. Anyways, you can test it in circuit and if you do not
see a virtual short then replace it. On the other deflection board, the problem was a loose 1/2
watt, 2.2k resistor (R606) in the Y amp. Its intermittent contact was causing the spot killer to
flicker, and was causing picture to collapse. The solder joint did NOT look cold or bad, and the
resistor tested fine. These resistors take a good deal of heat, and the traces they are on can heat
up pretty good. I found that it was loose by pushing on the top of the resistor a bit, and began to
hear a "tick" where the resistor lead was touching the solder joint. Probably the trace's