In this video number {1299A} LCD TV power supply function, circuit diagram & troubleshooting Explained. LCD TV Power Supply Function and Troubleshooting Explained. I explained working, testing and troubleshooting 715G4750-P04-000-001S power supply circuit board. it is used in ACL and Philips TVs and monitors. I explained working principle by reverse engineering the circuit and making circuit diagram. i eplained cold testing, live testing and check points.
If you're troubleshooting a 715G4750 Power Supply Board (common in Philips, AOC, and some other LCD/LED TVs), here’s a practical guide:
715G4750 Power Supply — Common Fault Symptoms:
TV Dead, No Standby Light
TV Turns ON, but No Display or Backlight
Output Voltages Fluctuate or are missing
Fuse Blown or visible burn marks
TV turns off after a few seconds (protection mode)
First of all perform Visual Inspection. Look for bulged, swollen, or leaking capacitors.
Check for burnt resistors or components. Inspect solder joints for cracks or cold solder, especially on transformers and power MOSFETs.
Check the Fuse. Test the main AC input fuse. If blown, inspect rectifier diodes and MOSFETs before replacing it. Test Bridge Rectifier & Main Filter Capacitor. Confirm the bridge rectifier is not shorted. The big capacitor (usually 400V 82–150μF) should charge properly. Measure DC after rectification — usually around 310V–330V if connected to 220V AC. Check Startup & Standby Voltages, Look for standby 5V output even when the TV is OFF.
If this 5V is missing, check. Primary side components (startup resistor, startup capacitor). PWM IC or optocoupler (often responsible for standby).
Check the Switching MOSFET. Test with a multimeter (diode mode) for short circuits between. Drain — Source.
Gate — Source. If shorted, replace and check surrounding components (gate resistor, PWM IC, snubber diode).
Secondary Side Output Voltages. Check the expected outputs:
5V standby. 16V for backlight circuit
If voltages are fluctuating. Test optocoupler feedback circuit.
Replace secondary capacitors — bad caps cause ripple and unstable voltage. Check Feedback and Protection Circuit. Optocoupler, zener diodes, and TL431 reference IC are common failure points. If the optocoupler is faulty, the power supply can’t regulate voltage and might go into protection mode.
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