General Troubleshooting; Circuit Board Troubleshooting - Zenith ZVM-1240 Service Manual

Table 1
General Troubleshooting
PROBLEM
Monitor completely dead.
No video (Power Indicator
is lit-High and Low
voltages are OK).
Insufficient brightness.
No raster.
Characters on screen
out of focus.
No horizontal sync.
Page 1.0
POSSIBLE CAUSE
1.
2.
3.
4.
5.
1.
2.
3.
Power cord not connected.
Power switch not on.
Fuse is missing or blown.
Power supply failure.
Shorted horizontal output.
Signal cable not connected
to computer.
Contrast control set to low.
CRT socket board defec-
tive.
4. Main circuit board defec-
tive.
5.
6.
1.
2.
3.
1.
2.
3.
4.
1.
2.
3.
1.
2.
Wiring between boards de-
fective.
No signal from the com-
puter.
Brightness control set to
low.
CRT socket board defec-
tive.
Main circuit board defec-
tive.
Brightness control defec-
tive.
Horizontal circuit/high volt-
age not working.
CRT socket board defec-
tive.
CRT defective.
Focus control defective.
CRT· socket board defec-
tive.
Main circuit board defec-
tive.
Horizontal hold control de-
fective.
Horizontal processor,
IC1 01 , defective.
Table 1 (contInued)
General Troubleshooting
PROBLEM
No vertical sync.
Vertical sweep scans
bottom to top.
Horizontal sweep scan
right to left.
POSSIBLE CAUSE
1.
2.
Table 2
Vertical size control defec-
tive.
Vertical processor IC301
defective.
Red and blue wires re-
versed on deflection yoke.
Yellow and black wires re-
versed on deflection yoke.
Circuit Board Troubleshooting
PROBLEM
No raster.
No video (Raster OK).
No vertical deflection.
No vertical sync.
POSSIBLE CAUSE
1.
2.
3.
4.
5.
1.
2.
3.
4.
5.
1.
2.
3.
4.
0102, TX102 (check high
voltage at CRT anode.
CR102, RX133, RX136.
0101,0102, TX101.
IC101.
VX201 CRT.
0201, 0202, 0204.
VX201, R402 Contrast
control.
CR103.
CRT socket.
Excessively high B + volt-
age. High.8+ will cause
0206 to conduct, killing the
video signal.
0301,0302.
IC301.
TX202A, yoke.
CR301.
CR302, 0301, 0302,
R323, R326, C312, C316.
Servicing