Omnivision PVQ-1300W, Service Manual

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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 3
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).
1. Immediately before handling any semiconductor component or
semiconductor-equipped assembly, drain off any ESD on your body touching a
known earth ground. Alternatively, obtain and wear a commercially available
discharging ESD wrist strap, which should be removed for potential shock
reasons prior to applying power to the unit under test.
2. After removing an electrical assembly equipped with ES devices, place the
assembly on a conductive surface such as aluminum foil, to prevent electrostatic
charge buildup or exposure of the assembly.
3. Use only a grounded-tip soldering iron to solder or unsolder ES devices.
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