Samsung LN32C540F2DXZA: Won't turn on, PS and Inverter OK

[beedoola]

Re: Samsung LN32C540F2DXZA: Won't turn on, PS and Inverter OK

Yes its a 8 pin dual n-channel mosfet from Alpha and omega number AO4800BL or AO4801. There should be 12 v or 11.8 v at pins 5,6,7 and 8 when the power button is pressed. If not check if you have any voltage at pin 2 and 4.

Usually these fet's don't fail but so far I've only seen one failure

I get 12V on 2, nothing on Pin 4.

3.3v on 5&6, nothing on 7 and 8.

It is a 4801A BADD1B

[myfastgti]

Re: Samsung LN32C540F2DXZA: Won't turn on, PS and Inverter OK

I get 12V on 2, nothing on Pin 4.

3.3v on 5&6, nothing on 7 and 8.

It is a 4801A BADD1B

You could try replacing the FET, eBay sells them for $2.

Unfortunately I don't have the service manual

[budm]

Re: Samsung LN32C540F2DXZA: Won't turn on, PS and Inverter OK

I get 12V on 2, nothing on Pin 4.

3.3v on 5&6, nothing on 7 and 8.

It is a 4801A BADD1B

How about pin 1 (Source 2), pin 3 (Source 1)? Those two pins are fed with Voltages which will go out on the Drain pin 5 & 6 for Drain 1, and 7 & 8 for Drain 2.
The Gate pins (pin 2 for G2, pin 4 for G1) Voltage has to be at least 2V less than the Source pin for the MOSFET (P-CH) to turn on.

A4801: Dual P-CH MOSFETs
Pin 1 = S2
Pin 2 = G2
Pin 3 = S1
Pin 4 = G1
Pin 5 = D1
Pin 6 = D1
Pin 7 = D2
Pin 8 = D2

[beedoola]

Re: Samsung LN32C540F2DXZA: Won't turn on, PS and Inverter OK

S2/Pin 1 also had 12, like Pin 2. Pin 3 had nothing. Where can I find a AO4801?

[beedoola]

Re: Samsung LN32C540F2DXZA: Won't turn on, PS and Inverter OK

Is it possible to jumper the pads to see if I can get proper power to the board?

[budm]

Re: Samsung LN32C540F2DXZA: Won't turn on, PS and Inverter OK

The readings you provided does not indIcate bad IC.
G2 has to be 10V or less for the MOSFET 2 to turn on, and you did not indicate any inout Voltage feeding S2 pin 1 either.
S1 pin 3 also no Voltage input either.

[beedoola]

Re: Samsung LN32C540F2DXZA: Won't turn on, PS and Inverter OK

Can it be assumed that since the voltages on the PS board are fine and the backlight comes on that the PS and inverter are OK and that the problem must lie somewhere on the Main Board?

[budm]

Re: Samsung LN32C540F2DXZA: Won't turn on, PS and Inverter OK

Can it be assumed that since the voltages on the PS board are fine and the backlight comes on that the PS and inverter are OK and that the problem must lie somewhere on the Main Board?

Yes, as indicated in post 8 that the main board is not sending the signal (PS_ON line stuck low) to turn on the power supply.

[beedoola]

Re: Samsung LN32C540F2DXZA: Won't turn on, PS and Inverter OK

got a replacement main board for $65 shipped so I'll see how it goes.