Service manual

Wells-Garnder Color Vector Monitor Guide
Page 27 of 73
HIGH VOLTAGE BOARD PROBLEMS
Symptom: Display Unstable
The image is extremely shaky and unstable and lines that should be straight have periodic
wiggles along their length that make them look like an EKG (the distortion is sort of like when
you watch TV with a bad antennae and lines "walk" around on the screen).
Replace C901, C902, and/or C905 in the HV supply. If one of these is bad then the rest of the
electrolytic capacitors are probably in pretty poor condition too, so I generally replace all of
them. Make sure the replacements are rated at as least as many "working volts DC" WVDC and
have as least as many microfarads. It does not hurt to replace a 22uF @ 50V capacitor with a
50uf @ 100V if that is all you have around. More Voltage capacity is equal or better but it is best
to keep the capacitance the same if you can. Also when ordering and replacing these, be aware
that they are polarized and not idiot-proof; be sure to put them in the circuit so that they are
oriented properly. The casing will clearly indicate either the negative or the positive terminal
(but typically not both) and the industry convention is for the positive lead of the capacitor to be
longer than the negative lead. Be aware that P329 has an extra capacitor (C22) that may not be
shown in your manual; its value is 10uf @ 63V.
Symptom: Picture Too Bright But All Else OK
The picture is overly bright and all parts check out OK.
Look for a broken circuit board trace between pin 6 of the high voltage transformer and the
anode of diode D901. This trace is prone to breaking open. It is probably easier to just add a
jumper and see if it solves the problem or else check the connection (with board removed) with a
meter to make sure it is a short.
Symptom: R925, R919, and R917 are Smoked
• Q905 (shorted; T901 primary may be shorted, too)
Symptom: R901, R907, R903 are Smoked and Q902 and ZD901 are Shorted
• Q901 (reversed)