Samsung UE40D5000 , completely dead!

[Moreno83]

Hey guys ,

It's been a while but i was given a dead 40 inch Samsung LED tv.
I dont know the history of the tv but there is no visible damage on the tv or boards.

I attached 2 pictures of the powerboard. Bottom and top of the board and i marked what i measured.
I got zero voltages on the connector going to the mainboard so the main problem must be in the "hot" area.

What i measured :

- zero voltage on the connector going to mainboard.
- +/- 312v on ac/dc converter and the 2 capacitors.
- +/- 312v between VCC and Drain on the SMPS ( 3BR1765JZ )
- Short on the pins from 2 mosfets ( ndf05n50zg ).
- zero voltage on the optocouplers.

I took the mosfets of the board and they are ok. The short is still present on the board.


Hope someone can help me. I could order a new PS but i would like to repair this one and learn a bit more about LED tv's.

[Moreno83]

Re: Samsung UE40D5000 , completely dead!

And no the backlights don't turn on with the mains connected and the mainboard disconnected. With just mains on the PS i got zero voltage.

[Moreno83]

Re: Samsung UE40D5000 , completely dead!

There is a DC DC converter on the back of the board. Also 0v going in. It's a TK11806M

[nomoresonys]

Re: Samsung UE40D5000 , completely dead!

So dead then, no led indicator lit on front, check all the diodes on powerboard, easy enough to check if you didn't already.

[Moreno83]

Re: Samsung UE40D5000 , completely dead!

Yes indeed , i did the basics and the diodes read fine. Just dont get the short on the board.

[diif]

Re: Samsung UE40D5000 , completely dead!

Here's the schematic.

[Moreno83]

Re: Samsung UE40D5000 , completely dead!

Thanks! Looking at the schematic and at the measurements im thinking it is best to take a closer look at "TS801" which is a transformer. I think that transformer turns the high voltages into lower voltages....

What do you think?

[R_J]

Re: Samsung UE40D5000 , completely dead!

The first voltage you need to check is the A5V standby voltage. You say you don't have this voltage, so it is likely ICS801S is bad
Check if you have 300+ voltage on pin 5, Then check if RS807 is open.

[Moreno83]

Re: Samsung UE40D5000 , completely dead!

Thanks for the help guys. Repaired the same model before with a bad mainboard but indeed , the standby voltage is missing. Think the mainboard turns on the 3.3v for the led.

Got a few spare Samsung PS. Could i just swap the transformers? What to look for?

[nomoresonys]

Re: Samsung UE40D5000 , completely dead!

DID you do the test in post #9 to test that switching regulator IC? and check the solder joints on the transformers, maybe check PCS801S and PCS802S optos for shorts.

[dick_barton]

Re: Samsung UE40D5000 , completely dead!

Do those 2 mosfets (post #1) face downward when viewed from the top of the power supply.
If they do then it looks like a Gate - Source short so possibly the BAV70's otherwise if they are OK it should read 47 ohms between gate and source

[budm]

Re: Samsung UE40D5000 , completely dead!

Hey guys ,

It's been a while but i was given a dead 40 inch Samsung LED tv.
I dont know the history of the tv but there is no visible damage on the tv or boards.

I attached 2 pictures of the powerboard. Bottom and top of the board and i marked what i measured.
I got zero voltages on the connector going to the mainboard so the main problem must be in the "hot" area.

What i measured :

- zero voltage on the connector going to mainboard.
- +/- 312v on ac/dc converter and the 2 capacitors.
- +/- 312v between VCC and Drain on the SMPS ( 3BR1765JZ )
- Short on the pins from 2 mosfets ( ndf05n50zg ).
- zero voltage on the optocouplers.

I took the mosfets of the board and they are ok. The short is still present on the board.


Hope someone can help me. I could order a new PS but i would like to repair this one and learn a bit more about LED tv's.

1) What did you use for GND ref when making the measurement in the HOT side?
2) 230VAC power source should give about 325VDC when measure between the two legs of the main filter caps.
3) " +/- 312v between VCC and Drain on the SMPS ( 3BR1765JZ )" Strange way of testing the Voltage. What is the Voltage between VCC and the hot side circuit GND?
4) "Short on the pins from 2 mosfets ( ndf05n50zg )" So you are saying that teh resistance between the GATE and Source pin of those two MOSFET fpor the PFC are showing < 1 Ohm?

[Moreno83]

Re: Samsung UE40D5000 , completely dead!

1) What did you use for GND ref when making the measurement in the HOT side? Negative leg cap/or GND from SMPS.

2) 230VAC power source should give about 325VDC when measure between the two legs of the main filter caps. I measure 315V

3) " +/- 312v between VCC and Drain on the SMPS ( 3BR1765JZ )" Strange way of testing the Voltage. What is the Voltage between VCC and the hot side circuit GND? Sorry my bad , voltage is fluctuating between 12 and 15v. Between GND and VCC( bouncing )

4) "Short on the pins from 2 mosfets ( ndf05n50zg )" So you are saying that teh resistance between the GATE and Source pin of those two MOSFET fpor the PFC are showing < 1 Ohm? It's beeping and showing 48ohm.

There is 315V going into the transformer ( MQGAH033310 ) and nothing is coming out so i think that this is the problem.

[dick_barton]

Re: Samsung UE40D5000 , completely dead!

You say inpost #1

- Short on the pins from 2 mosfets ( ndf05n50zg ).

and then in post #13

4) "Short on the pins from 2 mosfets ( ndf05n50zg )" So you are saying that teh resistance between the GATE and Source pin of those two MOSFET fpor the PFC are showing < 1 Ohm? It's beeping and showing 48ohm.

So the 48 ohms is correct

I would do the checks RJ suggested and also check (VCC) between pins 7 and 8 of that IC

[nomoresonys]

Re: Samsung UE40D5000 , completely dead!

Can you post a close up picture of the bottom of the board in that transformer area?

[R_J]

Re: Samsung UE40D5000 , completely dead!

There is 315V going into the transformer ( MQGAH033310 ) and nothing is coming out so i think that this is the problem.

LP801S is not a TRANSFORMER it is a COIL! LOOK at the F#@$ SCHEMATIC, If you have 312 volts on the caps how can the coil be bad?

[nomoresonys]

Re: Samsung UE40D5000 , completely dead!

My picture request was for the transformers starting with indicators TM, may not be your problem but sometimes a solder bridge breaks and you get similar symptoms, it's troubleshooting, not always easy.

[Moreno83]

Re: Samsung UE40D5000 , completely dead!

The first voltage you need to check is the A5V standby voltage. You say you don't have this voltage, so it is likely ICS801S is bad
Check if you have 300+ voltage on pin 5, Then check if RS807 is open.

I got 315v on pin 5. RS807 is open.

[Moreno83]

Re: Samsung UE40D5000 , completely dead!

My picture request was for the transformers starting with indicators TM, may not be your problem but sometimes a solder bridge breaks and you get similar symptoms, it's troubleshooting, not always easy.

Thanks , i already noticed that the solder wasn't that great so i reflowed most of the board.
I also replaced the 47uf and 22uf caps just to be sure.

Hope someone can help me , im not that great with fault finding in powersupplies. I'm more plasma tv's....

[nomoresonys]

Re: Samsung UE40D5000 , completely dead!

Did you replace that resistor?