Samsung power board BN96-03775A

[NicolaPO]

Hi guys, I'm trying to fix a Samsung LCD TV board.
Power Board is Model BN96-03775A.
When I connect to the 220v mains, the blue light flashes.
I tried to measure the voltages: 24v, 13v, 12v and 5v are missing but 5.8v standby is present.
I removed the card from the TV and connected a 1000 ohm resistor between STBY and PS / On to simulate switching on with load.
On the CP812 terminals there are 309v so the PFC is not working.
There are 396v on the cathode of DS801.
On the cathode of DS803 there are 33v and on DS802 12v.
I checked diode bridge BD801S OK, mosfet QP801S OK and diode DP819 ok. On the cold side of the anode and cathode of the optocouplers there are 5.8v.
I ask for help to find the problem: what can I measure and test in search of the fault?
I attach the schematic part of the service manual: in black there are the voltages when I connect the mains, in red when I connect a 1000 ohm resistor between PS / ON and STBY. Thanks for any help!
Nicola

[lotas]

Re: Samsung power board BN96-03775A

Your PFC is assembled on TDA4863, check its VCC power supply, there were cases when the QS802 transistor was leaking, and as a result, the VCC power supply was lowered.

[lotas]

Re: Samsung power board BN96-03775A

You also need to check the garlands of resistors, each must be evaporated and its resistance checked.

[NicolaPO]

Re: Samsung power board BN96-03775A

Your PFC is assembled on TDA4863, check its VCC power supply, there were cases when the QS802 transistor was leaking, and as a result, the VCC power supply was lowered.

Thanks for your reply, Lota. At Pin VCC 8 of TDA4863 there are 9.48v, as in the emitter of QS802: Do you recommend me to check QS802? Ok to try all the resistances you indicated in the diagram.

[lotas]

Re: Samsung power board BN96-03775A

Your Vcc is too low.