Stand-By Power Supply; Main Power Supply - Toshiba 1997 G Series Troubleshooting Manual

Color television power supply and shutdown

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2. Stand-by Power Supply

The stand-by power supply supplies 12Vdc to the re-

lay SR81, 5V to the microprocessor, 5V to the protect

IC, and a reset 5V to the microprocessor. T840 sup-

plies a low AC signal to D840. D840 rectifies the sig-

nal and C840 filters it to produce 12Vdc. The 12V is

applied to Q840. Q840 outputs a regulated 5V on pin 5

and supplies a reset 5V at pin 4. Reset occurs when

power is first applied to Q840. The 5V on pin 5 comes

up first while pin 4 stays low. This is the reset condi-

tion. After C843 fully charges, pin 4 goes to 5V for

normal operation.

* T r oubleshooting Ti p :

A loss of the 5 V or reset 5V will prevent the

microprocessor from operating.

1. Main Power Rectifier Circuit

D801 and C810, the rectifier and filter for the main

switching supply, produce 165V. R810 suppresses the

rush current at turn on. SR81 is a relay that turns on the

main supply. The relay is controlled by the micropro-

cessor through the relay drivers: QB30 and Q843.

* T r oubleshooting Ti p :

Because the microprocessor controls the relay, the

main power supply may not turn on if the micro-

processor does not operate properly.

Fig. 2 Rectifying circuit and standby power

165V DC

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