Mitsubishi Electric HITACHI VS-50111 Troubleshooting Manual page 25

Switched Supply Regulator
The Switched Supply Regulator is illustrated in Figure
5. IC9A50 is the Switch Supply Regulator and func-
tions the same as that in previous TVs. Approximately
16 volts at pin 4 of the IC is required to start the oscil-
lator.
The source of the start up voltage is the secondary wind-
ing at pin 2 of T9A20, the Standby Regulator Trans-
former. The signal from pin 2 of T9A20 is rectified by
D9A24, generating approximately 20 volts. The 20 volts
is directed to the collector of Q9A50 and the collector
of the Photo Transistor at pin 8 of PC9A50.
When the set is switched On, the P-ON line from the
Control Circuit goes High turning Q9A51 On, which:
• Closes relay K9A50
• Lights the LED at pins 5 and 6 of PC9A50.
K9A50 shorts out the current limiting resistor, R9A02.
The light from the LED turns On the Photo Transistor at
pins 7 and 8 of PC9A50. The conduction of the Photo
Transistor turns Q9A50 On, suppling start up voltage
to pin 4 of IC9A50.
As soon as the oscillator in IC9A50 starts, the DC volt-
age at pin 4 drops. To maintain the DC supply at pin 4,
the signal from the secondary winding at pin 3 of T9A50
3-5
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