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Within the P board, this High is applied to the relay driver Q842 through the current
limiting resistor R886. Q842 energizes the main AC relay RL802 so its contacts apply
voltage to two power supplies:
1. Ballast Power Supply – produces regulated 330Vdc
2. Main TV Power Supply – produces 10 voltages necessary for TV operation.
5 volts from the Main Power Supply is also used to energize the surge relay so that the
surge resistor (R801) is bypassed after power-on.
Troubleshooting Scenarios
Symptom - Dark screen, no audio. The power LED either is off or continues to blink.
Refer to figure 8.
a. Power LED Off, no relays click - If the Power LED does not light up when the
power button is pressed (normally blinks green), there is no standby power going
to the microprocessor IC1103.
Check for standby 7V, leaving the P board at P5/pin 9. If the voltage is missing,
remove the load, by unplugging the P5 connector and measure P5/pin 9 (board).
Without a load, the standby 7V source normally measures 12Vdc. If the voltage
is missing or low, the problem is on the P board.
b. Power LED blinks continuously, no relays click - If there is a blinking green power
indicator, but no relays click when the power button is pressed, the power-on
signal output from the microprocessor, at DG2/pin 5 is not getting to the power
relay RL802.
Check for constant 5Vdc at P4/pin 1 after the power button is pressed (while the
green power LED blinks). If this P4/pin 1 voltage is missing, work backwards to
its source at DG/pin 5.
However, if this P4/pin 1 voltage is present, the problem is on the P board (Q842,
RL802, low standby voltage, etc).
c. Power LED blinks continuously, relays click - If there is a blinking green power
indicator, but the relay(s) do click, the Main Power Supply or / and the ballast
supply is not working. Microprocessor IC1103 monitors both supplies and shuts
off the TV relay (RL802) if either 3.3Vdc from the Main Power supply or the lamp
ballast current is missing. Find out which power supply is not working.
Check voltages from both the power supplies to determine which is not working.
d. Power LED blinks in a pattern and repeats itself, relays click (TV on) once and
click again (TV off) - TV is shutting down. The protection circuit has sensed a
problem and is shutting down the TV. An example in this diagram is at P5/pin 3
that monitors 3 voltages from the power supply board. See the protection circuit
section of this book.
Voltage Distribution
The purpose of the voltage distribution diagram (figure 9) is to show the loads
connected to each power supply line. From this you can see what boards can load
down (short) the individual power supply voltages from the P board to cause the TV to
shutdown. Disconnecting the individual lines or measuring for low resistance is useful
for locating the short that caused the TV to shutdown.
14
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