Samsung PS50A656T1FXXC PSU: BN44-00222A

[Bobo360]

Re: Samsung PS50A656T1FXXC PSU: BN44-00222A

The 5.3 volts should supply 7 amps, 5Ω across it would be about 1 amp.
The Va should be able to supply 1 amp, 120Ω should draw about 1/2 amp. If that shuts down the power supply it is time to look at the primary of that circuit and why it can't supply the curent.
If cx810 goes bad or weak it can cause this issue, If you don't have a replacement I would try and exchange it with either CS810 or CS811 and see if the 5.3 becomes stronger

I changed the CX810 capacitor with a new one.
But from the same problem.
I did an extra test, I put the 120 Ohm resistance between Va and GND, I have no problem.

In your opinion, can I put the 5 Ohm resistor between the central pin of the DX805 and GND?

Because I think it can be him or the mosfet QX807 and QX808.

Because I know that we can exclude the primary, since Va works.

What do you think?

Thank you

[Bobo360]

Re: Samsung PS50A656T1FXXC PSU: BN44-00222A

I have done other tests;

I connected between the pin of the DX805 and mass, various resistors:

1. -> 8.9 Ohm, and everything works.
2. -> 5.6 Ohms and everything works well, even if 5.3 is not immediately stable. But then it stabilizes.
3. -> 3.3 Ohm and everything works well.

I make a list of everything I've changed so far, without solving.

CX824, CX823, CX826, CX837, CX838, CX835, CX834, CX822, CX811, CX812.

If, on the 5.3V, I insert a resistance of 8.9 Ohm, it must be blocked immediately.
If I insert a 120 Ohm resistor (there is an absorption of about 40 mA), it works for almost a minute and then goes to lock.

[Bobo360]

Re: Samsung PS50A656T1FXXC PSU: BN44-00222A

I want to write to you because I solved the problem.

I changed then:
CX822, CX819, CX817, CX826, CX834, CX835, CX823, CX824, CX812, CX811, CX841, CX825, CX812, CX820, CX837
and also the big CS813.
Some are small and non-electrolytic.

I changed them in steps, not all together, to see how it went.

So I decided to go a little bit upstream of the circuit and install a resistance and see the absorption.
Starting from a small amperage.

Type at the output of the DX805 that there are about 9 / 10Volt, I was absorbing 1A, 1.5A and 2.5A.
Then before the QX807 mosfet in the same way.
Then after the QX807 but before the CX837 and the QX808.
Then after the QX808, but increasing the amperage.
Finally just before the CX835 with a 1ohm resistance to absorb about 5A it held quite well.

so I disconnected everything connected to the motherboard and logic board and all is well.

Following the circuit I had made a card, which I attach, so that I could make these arguments.

But I wonder why it came back to work by passing some current increasing from time to time?
Any mosfets blocked? or what?

Thanks a lot.

[zape]

Re: Samsung PS50A656T1FXXC PSU: BN44-00222A

It looks like I have similar symptoms.
Will try to replace the caps

[shaycago]

Re: Samsung PS50A656T1FXXC PSU: BN44-00222A

Do you by any chance have a photo of the back of this board? Mine is so burnt I'm not sure where the solder lines run. Thanks in advance.

[budm]

Re: Samsung PS50A656T1FXXC PSU: BN44-00222A

Do you by any chance have a photo of the back of this board? Mine is so burnt I'm not sure where the solder lines run. Thanks in advance.

https://www.shopjimmy.com/samsung-bn...upply-unit.htm

[michaszek]

Re: Samsung PS50A656T1FXXC PSU: BN44-00222A

Hello from Poland here. I also have lower voltage 4.3V instead 5.3V on this board. Any load connected to this line put the board in some clicking-test mode and ends with two green blinks. And worth noticing there is high pitch noise coming from the board once it is switched on by shorting 5V STB to GND. Circuit for generating this 5.3V is on the green-solder side of the board: controller L6725 + two mosfets: STS25NH3LL. In my case I've checked caps and diodes around and they seems to be ok, but QX807 seems to have shortage between GATE and SOURCE, second one QX808 doesn't have it, seems to be ok. I decided to replace both mosfets with BUZ11 mosfets as I have it around. Also there is a chance that controller L6725 is broken, but I do not have it and will start from replacing the mosfets.

[michaszek]

Re: Samsung PS50A656T1FXXC PSU: BN44-00222A

Hello. It was the right direction. QX807 was faulty shorted. I replaced it with some other similar n channel MOSFET and now the TV works.

[Bobo360]

Re: Samsung PS50A656T1FXXC PSU: BN44-00222A

I'm happy for you. These mosfets are joking ...