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.
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 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 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
3. PREVENTION OF ELECTROSTATIC DISCHARGE
(ESD) TO ELECTROSTATICALLY SENSITIVE (ES)
DEVICES
Some semiconductor (solid state) devices can be damaged easily by static electricity. Such
components commonly are called Electrostatically Sensitive (ES) Devices. Examples of typical
ES devices are integrated circuits and some field-effect transistors are semiconductor "chip"
components. The following techniques should be used to help reduce the incidence of
component damage caused by electrostatic discharge (ESD).
6
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