• Set is dead, and makes no sound
Check power supply IC 7520. Result: voltage at pins 1,3, 4, 5 and 6 are about 180 V
and pin 8 is 0 V. The reason why the voltage on these pins is so high is because the
output driver (pin6) has an open load. That is why MOSFET 7521 is not able to
switch. Reason: feedback resistor 3523 is defective. Caution: Be careful measuring
the gate of 7521; circuitry is very high ohmic and can easily be damaged!
• Set is in hiccup mode and shuts down after 8 seconds Blinking LED (set is in
SDAM mode) indicates error 5. As it is unlikely that P "POR" and "+8V
protection" happen at the same time, measure the"+8V" supply. If this voltage is
missing, check transistor7480.
• Set is in non-stop hiccup mode
Set is in over-current mode; check the secondary sensing (optocoupler 7515) and the
"Main Power Supply" voltage. Signal "Stdby_con" must be logic low under normal
operation conditions and goes to high (3.3 V) under standby and fault conditions.
• Set turns on, but without picture and sound
The screen shows snow, but OSD and other menus are okay. Blinking LED
procedure indicates error 11, so problem is expected in the tuner (part reference
number 1000). Check presence of supply voltages. "Vlotaux+5V" voltages at pin
5 and 7 are okay; "VT_supply" at pin 9 is missing. Conclusion: resistor 3460is
defective.
• Set turns on, but with a half screen at the bottom. Sound is okay
Blinking LED (set is in SDAM mode) indicates error 3. Check"Vlotaux+11V" and
"+50V". If they are okay, problem is expected in the vertical amplifier IC 7471.
Use an oscilloscope to measure the waveform on pin 17 of the UOC. Also
measure the waveform at pin 1 of IC 7471. If the signal there is missing, a
defective resistor R3244 caused the problem.
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