Samsung UN58J5190AFXZA pwr supply troubleshooting help

[momo2000]

Set stopped working. Doesn't power on and no standby light on the front. I read the forums, and believe it is the power supply board failure. Photos attached, and visual inspection does not reveal an obvious problem (at least to me).
While plugged in, I test the voltage at the connector (CNM803) that goes to the main board. Voltage on 1-2, 3-4, 5-6, 7-8 is 1.34VDC. 9-10 is of course ground. This test leads me to believe that the PS has failed.

Also research says that model has a high LED failure rate, so am guessing that is what has caused the PS failure. So after I solve the PS problem, I will have to chase the LED problem. I would like to do a board level repair of the PS if possible, since I'll then have to invest in LED strips.

Any suggestions on how to solve the PS problem?

[petehall347]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

test the diodes .

[momo2000]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

test the diodes .

Thanks for the reply! Are you referring to these 4 components that I have highlighted in the attached photo? My multimeter does have a diode setting, but I have never used. Am I just checking to see if they are open?

[budm]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

https://www.badcaps.net/forum/attach...0&d=1598658102

See that jumper J846 that has label: STB:8V ON:13V, what do you get on that jumper?

[budm]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

Set stopped working. Doesn’t power on and no standby light on the front. I read the forums, and believe it is the power supply board failure. Photos attached, and visual inspection does not reveal an obvious problem (at least to me).
While plugged in, I test the voltage at the connector (CNM803) that goes to the main board. Voltage on 1-2, 3-4, 5-6, 7-8 is 1.34VDC. 9-10 is of course ground. This test leads me to believe that the PS has failed.

Also research says that model has a high LED failure rate, so am guessing that is what has caused the PS failure. So after I solve the PS problem, I will have to chase the LED problem. I would like to do a board level repair of the PS if possible, since I’ll then have to invest in LED strips.

Any suggestions on how to solve the PS problem?

Pin 8 is GND so I cannot see how you get 1.34V, and to have all those pins showing 1.34V it must be measurement error.

It looks like you count the pins wrong, please look at the chart.
Odd pins are the exposed pins you can see from the top side of the board, the even pins you have to use skinny probe to probe from wire entrant side of the connector.

[nicholas1110]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

Hello,
It is very common for this board to fail when the leds short. Normally QP801CS on the back of the board is shorted. This is usually the only part that needs to be replaced ( other than the leds) to get it back running. Hope this helps

[momo2000]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

budm: the J846 measures 1.34VDC as well.
budm: Sorry for the confusion, I just re-measured, pins 1,3,5,7 all measure 1.34VDC.

[momo2000]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

Hello,
It is very common for this board to fail when the leds short. Normally QP801CS on the back of the board is shorted. This is usually the only part that needs to be replaced ( other than the leds) to get it back running. Hope this helps

Is QP801CS testable with a multimeter?

[budm]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

What dc Voltage do you have on the main filter cap 120uF 450VDC when measured between the two legs?

[momo2000]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

What dc Voltage do you have on the main filter cap 120uF 450VDC when measured between the two legs?

I measured the "main filter cap 120uF 450VDC", circled in red below, and it was 166VDC.

[momo2000]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

I measured the "main filter cap 120uF 450VDC", circled in red below, and it was 166VDC.

budm: any thoughts? I reported back the measurement, please let me know what you think. Thanks so much.

[budm]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

So the circuit does have Voltage to run the SMPS but the SMPS is not working properly, in standby the the standby Voltage should be 8V and when PS-ON is present the PFC Boost Voltage (around 380 ~ 400VDC on the main filter cap) and the standby output should be 13V.

I or someone need to trace out the board to be able to give you test points for you to test next.

[momo2000]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

So the circuit does have Voltage to run the SMPS but the SMPS is not working properly, in standby the the standby Voltage should be 8V and when PS-ON is present the PFC Boost Voltage (around 380 ~ 400VDC on the main filter cap) and the standby output should be 13V.

I or someone need to trace out the board to be able to give you test points for you to test next.

OK, thank you, I stand at the ready to test and would be most grateful!

[nicholas1110]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

Have you tested the transistor I mentioned? Remove the board from the tv. On the back of the board is the smd transistor in the location I mentioned before. Put your meter in diode mode, check for short between the center pad and the 2 legs. If your meter reads close to 0.0 it is shorted. If it reads around 0.40 then it is likely good.

[budm]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

QP801C (P = PFC) is the MOSFET for the PFC boost Voltage circuit, If it is shorted out then the main fuse will blow, if it not shorted but not working then there will be no boosted Voltage.
MOSFET is not tested like BJT.

[momo2000]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

Have you tested the transistor I mentioned? Remove the board from the tv. On the back of the board is the smd transistor in the location I mentioned before. Put your meter in diode mode, check for short between the center pad and the 2 legs. If your meter reads close to 0.0 it is shorted. If it reads around 0.40 then it is likely good.

nicholas1110: Thanks for the instructions. I cannot find “QP801CS”. I do have a QM801CS. I have attached a photo highlighting this component, is this the correct one? I removed the transistor at that location and tested with my multimeter in diode mode. Here are the results:
-Pos lead on left leg, and neg lead on center leg is OL, or no current flow.
-Pos lead on right leg, and neg lead on center leg is starts at .45 and increases to .65 over a 30 sec period.
For clarity the “legs” are the 3 lead all in a row on the bottom, NOT the pad at top, which I assume is a heat sink.

[momo2000]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

QP801C (P = PFC) is the MOSFET for the PFC boost Voltage circuit, If it is shorted out then the main fuse will blow, if it not shorted but not working then there will be no boosted Voltage.
MOSFET is not tested like BJT.

Budm: OK, thanks for the explanation. I “think” I understand.

[budm]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

Budm: OK, thanks for the explanation. I “think” I understand.

QP801C is mounted on the heatsink.
The one you removed is also MOSFET, there are two of them as you can see, they are for driving the power transformer.

[nicholas1110]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

Check out this thread, it should be related to the same part number power supply as yours.
https://www.badcaps.net/forum/showthread.php?t=64699

[momo2000]

Re: Samsung UN58J5190AFXZA pwr supply troubleshooting help

budm and nicholas1110: I have located, desoldered/removed and tested the QP801CS (was screwed to the heatsink).
I have tested with my multimeter in diode mode and below are the results:
Pos on Source (left), Neg on Drain (center) = .544
Pos on Source (left), Neg on Gate (left) = OL

I think this means it is good, right? I was hoping it would be bad, as now I am not sure where to go, any suggestions?