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2.1. 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 120 V AC power source to the set,
turn on the set.
2. Set the customer controls to normal operating positions.
3. Short between TP891 and TP892 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.
2.2. 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 +21.5 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.
2.3. CIRCUIT EXPLANATION
2.3.1. 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 Transformer 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 become dark in order
to keep X-radiation under specification.
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