TM 9-6625-1753-14
C2
Table 5-3. Troubleshooting Dual Trace Plug-In Type 76-02A
Malfunction
Probable cause
Corrective action
No vertical trace on the CRT
Open interlock circuit because the unit
Reinsert the unit, making sure
the
screen.
connector is not plugged in the main
connectors are properly mated.
frame connector properly.
Defective capacitor C9709 in the
Replace the capacitor.
blanking circuit.
Defective transistors in the blanking
Check Q9701, Q9702, Q9703, and
circuit.
Q9704 and replace the defective
transistor (fig. 5-7).
Vertical trace appears on the CRT
For channel A only: GAIN ADJ control
Readjust GAIN ADJ control.
screen, but it has insufficient
R9212 is not adjusted properly.
amplitude.
Defective stage
or
stages
in
the
Check stage-by-stage from Q920 and
Q9206 back to the input via Q9202,
Q923, Q9201, Q99200, V921, and
V920 and replace the defective
transistor, tube, or component (fig.
Measure the voltages as shown on the
functional schematic to help isolate the
defective stage.
For channel B only: GAIN ADJ control
Readjust GAIN ADJ control.
R9312 is not adjusted properly.
Defective stage or stages in the
Check stage-by-stage from Q9304 and
Q930 back to the input via Q9303,
Q9302, Q9301, Q9300, V931, and
V930 and replace the defective
transistor, tube, or component (fig.
Measure the voltages at the same points
on channel B as shown in the
functional schematic for channel A to
help isolate the defective stage.
Both channels: Defective
common
Check stage-by-stage from Q9409 and
output amplifier stages.
Q9408 back to Q9401 and Q9400 via
Q940, Q9104, Q9414, Q9413, Q9403,
and Q9402 and replace the defective
transistor or component (fig. 6-9).
Measure the voltages as shown on the
functional schematic to help isolate the
defective stage.
MODE switch in CHOP position,
Defective MODE switch.
Replace switch 960.
only one channel is displayed.
Defective diode CR9704 in the blanking
Replace diode.
circuit.
Defective transistors in the blanking
Replace Q9701, Q9702, Q9703, and
circuit.
Q9704 (fig. 5-7).
Defective transistors or components in
Replace Q9600 and Q9601 or the
the electronic switch circuit.
defective components (fig. 5-7).
MODE switch in ALT position, only
Defective MODE switch.
Replace switch S960.
one channel is displayed.
Defective switching diodes CR9201 or
Replace switching diodes.
CR9301,
depending
on
which
channel is not displayed.
5-4
