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D board Circuit Failure Detection
If the unit shuts down but the standby light does not blink, the problem is in
one of the seven remaining areas that are not monitored by IC3251. Five
of these items are on the D board. Three of these items are shown in
Protection Circuit 4. However all five items are checked in this procedure:
1. Monitor the shutdown trigger voltage at the D board connector CN4001/
pin 9. If this voltage rises above the normal 0.3V to about 1.3V, the
problem is caused by one of the sensing circuits on this D board.
2. Locate Q4005/collector (middle lead). Monitor the voltage here as you
turn on the set and it shuts down. Normally this point will rise to 0.022V.
If it continues to rise to the trip point of 1.5V, the problem is excessive
driver PWM voltage from Q4003 or the Q4001/Q4005 sensing circuit
is defective. (Protection Circuit 3 diagram)
3. Locate the photo coupler PH4006/pin 3 and monitor its voltage as you
turn on the TV and it shuts down. The normal voltage here is 0V. If it
rises to the trip point of 1.5V, the problem is a shorted IC4003 center-
ing IC (Protection circuit #3 diagram).
4. Locate Q7003/collector (middle lead) or the anode of D7102 and moni-
tor its voltage as you turn on the TV and it shuts down. The normal
voltage here will not rise above 0V. If it rises to the trip point of 1.5V, the
problem is excessive current to the PWM regulating circuit, FBT or
Horizontal Output Transistor (Protection circuit #4 diagram).
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5. Locate IC4004/pin 14 and monitor its voltage as you turn on the TV
and it shuts down. The voltage here will rise to +8.35V and stay there.
If it rises and comes down just before shutdown, the problem is ex-
cessive voltage from the horizontal output PWM stage caused possi-
bly by a shorted Q4022 PWM Output MOSFET or the IC4004, D7029,
Q7001 and Q7003 sensing circuit (Protection Circuit 4 diagram).
6. Locate IC7001/pin 8 and monitor its voltage as you turn on the TV and
it shuts down. The normal voltage here will not rise above 0V. If it
rises to the trip point of 1V, the problem is excessive FBT voltage. A
possible defect is an open resonate capacitor in the Horizontal Output
Transistor's collector circuit.
7. If all these voltages are normal, yet CN4001/pin 9 rises to 1.3Vdc, the
problem is on the D board and Q4050 is probably defective (Protec-
tion Circuit 4 diagram). This is because it is the only part not yet
checked.
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