Panasonic Omnivision VHS PV-C2780, Руководство по обслуживанию

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HORIZONTAL OSCILLATOR DISABLE CIRCUIT TEST SERVICE WARNING :
The test must be made as a final check before set is returned to the customer.
CONFIRMATION OF X-RAY MOVEMENT
1. Turn off TV set.
2. Connect the circuit below between TP1209 and TP1208.
Figure 2
3. Turn on DC Power, and then turn on the set. Confirm that the
picture is on the screen properly.
4. Confirm that the picture goes out of horizontal sync while getting
down the voltage to DC Power.
5. If this does not occur even when getting down the voltage of DC
Power to 0 V, it means that X-ray protect circuit is not operating.
Further confirmation and repair is required.
REPAIR PROCEDURES OF HORIZONTAL OSCILLATOR DISABLE CIRCUIT
1. Connect a DC voltmeter between capacitor C513 (+) on the Main
circuit board and chassis ground.
2. If approx21.5 V is not present at that point when 120 V AC
is applied, find the cause. Check R503, R5505, C5507, C513 and
D503.
3. Carefully check above specified parts and related circuits and
parts. When the circuit is repaired, try the horizontal oscillator
disable circuit test again.
CIRCUIT EXPLANATION
HORIZONTAL OSCILLATOR DISABLE CIRCUIT
The positive DC voltage, supplied from the D503 cathode for monitoring high voltage, is applied
to the IC5301 Pin11 through R503 and R5504. Under normal conditions, the voltage at IC5301
Pin 11 is less than approx 6 V. If the highvoltage at Flyback Tr Pin 5 exceeds the specified
voltage, the positive DC voltage which is supplied from the D503 cathode also increases. The
increased voltage is applied to IC5301 Pin11 through R503 and R5504. Due to the increased
voltage at IC5301Pin11, the horizontal oscillator frequency increases, the picture goes out of
horizontal sync, the beam current decreases and the picture becomes dark in order to keep X-
radiation under specification.
Figure 3
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