Samsung PS50 plasma TV crackling noise

[mvata10]

Hi,
I have plasma TV Samsung PS50. From time to time it makes loud noise, now it is almost permanent and very annoying. I sent it for warranty service but they returned it I think without any repair. Now the warranty is gone and I decided to try to repair it myself.
1. the sound comes from power supply board BN44-00274B and is caused probably by the capacitor CP801 which is marked 2J 105J SIC 460S (see pictures 1 and 2)
2. a similar sound comes also from noise filter located in the power cord plug IF2-NO6AEW (see picture 3)
3. the noise filter is quiet while unplugged from power supply board
4. the CP801 makes noise even if the PSB is powered directly without the noise filter.

My questions are:
1. If I replace the CP 801, what part should I use - I can´t find the original part? An alternative for me is to change the complete board at much more price.

2. Should I replace also the noise filter at the same time or wait and see?

Thank you.

Martin

[tom66]

Re: Samsung PS50 plasma TV crackling noise

What equipment do you have - multimeter?

The crackling noise could be caused by the three capacitors mounted sideways at the top of the PCB. These are the PFC filter caps. If they fail, it can cause the PFC circuit to malfunction.

Can you test with varying brightness - from no signal screen to full brightness - and see if crackling increases with the picture brightness?

Also, unplug the speakers from the main board to eliminate them as a possible cause, just in case.

[mvata10]

Re: Samsung PS50 plasma TV crackling noise

Yes, the intensity of noise varies with the scene change, however, I would not say it depends only on the brightness.
I have only a simple multimetr, can you tell me how to test the capacitors?

Thanks
Martin

[tom66]

Re: Samsung PS50 plasma TV crackling noise

Can you hook it up to a laptop or computer using the VGA, and check if it does vary with brightness? This will be important in eliminating or including the PFC circuit in the failure analysis.

[mvata10]

Re: Samsung PS50 plasma TV crackling noise

1. I had to wait for 8-10 minutes for the noise to start after switching on the TV. Loudspeakers are disconnected.
2. There is no noise or almost none if a free channel with no signal is selected.
3. If there is a white or brighter area on the screen, the noise appears. I.e. simply going to menu increases the noise. The area may be small.
4. The noise if louder if the screen is white in VGA mode and cracling has higher frequency.
5. The biggest difference makes the switching off the energy saving and chosing dynamic mode of the picture. This makes the brightest picture and highest contrast with louder crackling with higher frequency.
6. I would bet the noise comes from the 2J105J capacitor. Would it be possible that the malfunction of the three PFC would start the noise in 2J105J and the noise filter?
Thanks.

[tom66]

Re: Samsung PS50 plasma TV crackling noise

Try taking a toilet roll or kitchen roll tube and use that to filter out unwanted noises. Are you sure it's coming from that cap? Also double and triple check that the mains power connector is well seated and cleaned - change the cord if possible.

[mvata10]

Re: Samsung PS50 plasma TV crackling noise

I think it is the 2J105J, I have used a tube for listening when searching for the source of the noise. I have also changed the power cord. The other possibility is that the failure is in the AC noise filter attached to the AC plug as the noise comes simultaneously also from it (and only simultanously). I can´t imagine how these two phenomenons could be interconnected. However, I used another cable to connect wires directly to the PSB bypassing thus the noise filter and the crackling was still present.

[tom66]

Re: Samsung PS50 plasma TV crackling noise

It seems to me like the PSU is drawing extra current occasionally, and the crackling is caused by this, if it is affecting the noise filter too. I would be hesitant to say replacing that cap would fix it. Can you try measuring the voltage across the main 3 caps. It should be around 400V when running and not dip much under load.

[mvata10]

Re: Samsung PS50 plasma TV crackling noise

First, I measured the main caps when the noise was present, there was 425 V in all of them. I did it once again when the noise was not there, and there was only 315 V in all of them. When the crackling started again, there was again 425 V.

[tom66]

Re: Samsung PS50 plasma TV crackling noise

425V is much too high and 315V is too low. Is your multimeter's battery ok? Can you try another battery? I suspect the caps as one possible cause.

[mvata10]

Re: Samsung PS50 plasma TV crackling noise

I do not have another battery of that kind. The meter reads 233 V at my AC outlet.
I also tried to simply test the caps with my simple multimeter on the resistance scale, the 3 caps charges at both polarities, the 2J105 only at one polarity. Don´t know it it means anything.

[tom66]

Re: Samsung PS50 plasma TV crackling noise

Try replacing the caps first. What is the rating on them? E.g. 220uF, 450V...

[mvata10]

Re: Samsung PS50 plasma TV crackling noise

450V 150uF

[tom66]

Re: Samsung PS50 plasma TV crackling noise

Try these - http://export.farnell.com/panasonic/...50v/dp/1198659

Just check diameter will fit.

[mvata10]

Re: Samsung PS50 plasma TV crackling noise

Thanks a lot. I will try it and write the result.

[mvata10]

Re: Samsung PS50 plasma TV crackling noise

I have changed the main caps and this did not resolved the crackling. Then I changed the 2J105J and again it did not helped. Then I removed the transformer left to 2J105 and the diode right to it and try to power the board and no problem - no noise - TV running normally. Then I put the transformer back and powered the board again - again no problem. When I put back the diode, noise again started. The diode is 1N40078 and is at the the input of VCC_PFC circuit. I will try to change it and if it does not work I go for a new or used working board.

[tom66]

Re: Samsung PS50 plasma TV crackling noise

TV ran normally without PFC section installed? I wouldn't have expected that, would have at least expected 100 Hz noise on display.

[mvata10]

Re: Samsung PS50 plasma TV crackling noise

TV ran normally as far as I could see. I did not wanted anything to burn out so I ran it only a short time, however, I did not notice any significant change. 100Hz noise would not be visible by the eye anyway, I think.

[tom66]

Re: Samsung PS50 plasma TV crackling noise

It would show as rolling bars. However, the main issue is the cheap Samwha caps have to take a lot more ripple current so they won't last which will eventually lead to problems.

If you upgraded the main capacitors to at least 1.5 x TV power consumption (ex. 450W max, so use 675uF or 680uF min) it would likely work fine from 230V. I would say though you should try to keep it as close to factory spec as possible.

[mvata10]

Re: Samsung PS50 plasma TV crackling noise

I have used 220 uF caps as the mains. I will try exchange the diode and see although I dont really think this will solve the problem. I would exchange also the trasformer however it seems to be impossible to get the right type. I have ordered a new board anyways.