Service manual

Wells-Garnder Color Vector Monitor Guide
Page 29 of 73
Symptom: R908 Smokes
• Q900 (white and black leads interchanged)
Symptom: R912 Smokes
• C910 (reversed)
• D901 (wrong value; perhaps ZD902)
Symptom: R917 Smokes
• Q905 (reversed)
If R920 smokes, check:
• C913 (bad; this can damage T901, too)
Symptom: No HV (Very Dead Sound)
No High Voltage (HV); you do not hear the crackling sound when you first turn the monitor on.
Check the transistors in the HV unit as described earlier. The ones I have seen fail most often are
Q903, Q902, and Q901 though they are all suspect. These transistors will usually have cracks in
the casing if they are bad so look closely at them. If all this stuff is OK, look at the electrolytic
capacitors.
One quick errata: The parts list in Figure 15 of TM-183 lists all capacitors as fixed axial-lead
when in reality, C905 is a radial-lead cap. These capacitors are designed to burst open (VENT)
when they fail due to overburdening (but they sometimes do not) so as to be obvious to
repairpersons. The top (for radial-leads) or the side (for axial-leads) will be open and some of the
"guts" will be hanging out. When some capacitors go bad, they sometimes take the final output
resistors R901 and/or R907 with them (but the resistors will look perfectly OK unless you check
them with a meter).
Also check to make sure that connector J901 inside the HV unit is intact; one person reported
that the plastic in his disintegrated on the inside and the wires came loose. If these are OK, check
the following: