Sony KDL-40CX520 2 LED flash Power Supply.

[diif]

So I have a Sony KDL-40CX520. I was told it had the LED flashing 4 times suggesting LED failure but upon receiving it and powering on the LED flashes in groups of two suggesting power supply.

I've done the trouble shooting as per the service manual and whilst there is the 3.3v standby voltage the 12v is missing. This suggests the power supply is at fault.

I get 346v across the main capacitors, have tested all the components I can and find nothing shorted.

Any ideas ? I can buy a power supply fairly cheap but I prefer to find the problem. Thanks.

[budm]

Re: Sony KDL-40CX520 2 LED flash Power Supply.

346VDC on the main cap when PS-ON is present?
If it is the the PFC Voltage is not working, I expect 380~400VDC range when PS-ON is present.
Can you read the P/N on the PFC IC?
Also check fusible resistor R301 which is for feeding the Boosted Voltage to run the 12V/24V SMPS section.
R401 is the fusible resistor for feeding Voltage to run the STBY power supply which is working at this point.

[diif]

Re: Sony KDL-40CX520 2 LED flash Power Supply.

Thanks budm, yes, 346v when on. Measured across the legs of one of the big caps.
R301 checks out ok.
There is an IC on the back of the board with 20113 marked on it. I'm guessing this is a R2A20113ASP.
I'm measuring 0.23v on it's input. Hmmmmm.

[jetadm123]

Re: Sony KDL-40CX520 2 LED flash Power Supply.

Pin 8 is the Vcc pin for that PFC chip and it requires at least 12Vdc for proper startup. There should be a small startup cap connected to that pin. Suggest you check it for proper capacitance/esr. Perform a resistance check between the Vcc and ground pins to see if it's internally shorted. Also, check the mosfet driven by the output pin as a shorted mosfet can damage that PFC chip.

[budm]

Re: Sony KDL-40CX520 2 LED flash Power Supply.

Check the switched transistor that is used for supplying VCC to that IC, the switched transistor gets the input Voltage from the AUX winding of the STBY SMPS transformer.