Philips PTV800, Руководство по обслуживанию

Страница: 111 / 567

Troubleshooting the High Voltage Power Supply
Loss of High Voltage can be caused by a failure in the drive circuits, beam current shutdown,
overvoltage, and loss of scan.
Check the dc voltage at on the anode of D901. If this voltage is less than one volt, the High
Voltage has been shut down due to a scan loss. Check the Horizontal and Vertical drive
circuits and the scan protection circuit. If the anode of D901 is 14 to 15 volts and Pin 8 of
IC900 is less than 4.4 or greater than 4.8 volts, check the feedback circuit.
Check Pin 6 of IC902. This voltage should be approximately 15 volts. If this voltage is low
(near zero volts), an overvoltage or overcurrent shutdown has occurred. Place an
Oscilloscope on the anode of D904 and observe the waveform as the set is turned on. If the
small pulse between the two large pulses moves, the unit is going into over voltage shutdown.
If the pulse does not move, the unit is going into over current shutdown.