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4. To prevent an X-Radiation possibly, it is essential to use the
specified picture tube.
HORIZONTAL OSCILLATOR DISABLE CIRCUIT TEST
SERVICE WARNING :
The test must be made as a final check before set is returned to the customer.
1. With the rear cover removed, supply about a 90 V AC power
source to the set, turn on the set.
2. Set the customer controls to normal operating positions.
3. Short both sides of R804 on the Main circuit board with a jumper
wire. Confirm that the picture goes out of horizontal sync.
4. If this does not occur, the horizontal oscillator disable circuit is
not operating. Follow the Repair Procedures of horizontal
oscillator disable circuit before the set is returned to customer.
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 approximately +21.0 V (For model with 13 inch CRT) or +21.9 V
(For model with 20 inch CRT) is not present at that point when 120
V AC is applied, find the cause. Check R518 (For model with 20
inch CRT), R503, R5504, R5505, D503, C513, C5507 and J5501.
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 3 V. If the high voltage 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 IC5301 Pin11, 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 2
6
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