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

[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.

[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

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

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

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

[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?

[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

[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

[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

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

[beedoola]

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

I had Samsung with similar problem and it turned out to be SDRAM was defective.

First heat the SDRAM with heatsink (Big red circle)chip for 30sec and see if the TV turns on if not check the 4 pin mosfet besides the RAM, sometimes it short.

4 Pin Mosfet or the 8 Pin IC you have circled?

I tested the pins on that IC and I can't tell if they're supposed to be but pins 5 and 6 are connected. I can't tell on the PCB if they're supposed to be.

pin 7 and 8 are also connected (i.e. show continuity test on my DMM) but I can clearly see they share trace.

[Ltank]

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

Sometimes when Main Board Silkscreen does not show pinout. Simply go to P.S. connection to main board. P.S. is labeled and trace it to the main board wire by wire. A royal pain but you can see what is supposed to be on that pin

[budm]

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

Quote:
Originally Posted by budm View Post
Do the resistance show as <1 Ohm? No Tv is not plugged in, right?
plugged in, Pin 2 is 54R, Pin 16 is 25R

unplugged they drop in resistance, after powering pin 2 is around 10M and drops, Pin 16 was less and drops over time."

When you do the resistance testing, DO NOT have power applied to the unit, you can also damage the meter if the unit has power.

[beedoola]

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

I had Samsung with similar problem and it turned out to be SDRAM was defective.

First heat the SDRAM with heatsink (Big red circle)chip for 30sec and see if the TV turns on if not check the 4 pin mosfet besides the RAM, sometimes it short.

Tried that and nothing happened, no shorts, as far as I can tell.

Do the resistance show as <1 Ohm? No Tv is not plugged in, right?

plugged in, Pin 2 is 54R, Pin 16 is 25R

unplugged they drop in resistance, after powering pin 2 is around 10M and drops, Pin 16 was less and drops over time.

[budm]

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

I heated up the board and that did not get it to power.

Pin 2 - Switch Power and Pin 16 - SW Inverter both are shorted to ground when the PS is hooked up.

When measuring the Main board without the PS connected, or anything else, those pins to do read as shorted to ground.

Do the resistance show as <1 Ohm? No Tv is not plugged in, right?

[myfastgti]

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

I had Samsung with similar problem and it turned out to be SDRAM was defective.

First heat the SDRAM with heatsink (Big red circle)chip for 30sec and see if the TV turns on if not check the 4 pin mosfet besides the RAM, sometimes it short.

[beedoola]

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

I heated up the board and that did not get it to power.

Pin 2 - Switch Power and Pin 16 - SW Inverter both are shorted to ground when the PS is hooked up.

When measuring the Main board without the PS connected, or anything else, those pins to do read as shorted to ground.

[budm]

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

See the picture attached.

[steves7839]

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

The legend follows the pinout. You can confirm this by checking the connector socket. Pin 1 is usually marked with a triangle or circle molded into the connector, and with silkscreen on the component side of the board.

[budm]

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

boards are all connected, no power to the TV then use hair dryer (heat gun will be to hot and may melt the plastic) to heat up the whole main board for 2~3 minutes then apply the power to see if it will come on.