50 Samsung (Hp-t5054) Completely Dead PSU

[Glitcher]

I got this plasma with a complete dead psu. Story with this, is it stopped working after a storm and power surge. No 5V standby voltage, no Vs, no Va.

All the fuses are good. The 4 Fets to the right heatsink of the largest caps (Qs/Qx 801, 802) do read short from source to gate, however removing them it seems to be coming from somewhere else on the board. I tested the typical problem with this model PSU, BN44-001612, with the FETs, smd transistors, and smd diodes and they all seem to be fine.

Checking the voltage across the two largest caps near the middle and they have no voltage at all! So checking the main fuse again just to be sure, it does have the 120VAC going through it.

I feel its something simple that I'm missing.

[Glitcher]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

photo of bottom near AC input

[tom66]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

No standby voltage, no relay click, no primary voltage.
Check the voltage across the small 450V cap (56 or 68uF from memory...)
Nothing there: check fuse to it.
Then check Vcc for standby controller.

[Ltank]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

Check the 5vdc without it the set will do nothing. There are relays the will click and then supply power to the bridge rectifier. If no 5vdc check the diode and capacitor in the circuit firts then the other parts of that circuit

[Glitcher]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

There is no 5V standby. I'm guessing the problem is somewhere in the primary side since there is no voltage across the large caps. Should I be able to test the psu out of the TV with only AC connected since its a primary issue?

Theres a 450V 33uf cap. It measures 53.6V across. The red fuse box next to it checks good.

Theres one IC in the underside of the board, is this the standby controller? its labeled A393F. I found a brief datasheet below, not sure if its the right one.. If I'm doing this right, measuring with reference to primary ground, VCC measures 0V.

[tom66]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

Is it BN44-00161 or 162?

161 sch

162 sch

[Glitcher]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

It came from a 50" so its a 162

[tom66]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

The 33uF has been replaced, originally 22uF and SAMWHA or SAMYOUNG. It should have about 160V across it, maybe it is open circuit?
Try checking voltage across CB813

[Glitcher]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

Looks like you got it! the 33uf cap is open circuit, would of never even guessed. I measured it with my esr meter and it won't even detect it (confirmed on a normal cap that meter is working).

CB813 measures 7.6V

So should I replace the cap with the original 22uf?
The tv was also said to have been repaired before and they paid $250 to get it fixed only for it to stop working again after a couple of weeks...

Do you think a power surge would of caused the cap to go open circuit? or is it because of the different value used when it was replaced?

[Glitcher]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

Just replaced the cap with a 22uf and the TV turns on now!

[tom66]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

Nice one! Sometimes the simplest of faults.
A 450V cap after a bridge, especially on a low power standby circuit, would normally have about 160V across it, with a bad cap, the voltage will be too unstable (too much ripple) and low.

[Glitcher]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

I knew it had to be a simple problem somewhere I missed. Thanks for the help

[mmartell]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

These stories make me warm and fuzzy

[lamouche1]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

sorry to get this topic back from dead I have a similar problem with a 50 inch here but I have the 5v standby i changed the 22uf 450V in case of a bad one. i do read between 3.3V and .244V on the PS-ON pin of CN801 i dont have any red led on the power button on the front of the tv i tried to force it to start grounding the ps-on pin no change i do have 21.35V at cb813. What you recommend next to check?

[ReeceyBurger123]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

What does Vs on do when you press the power button ?

[lamouche1]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

stay at 0v

[ReeceyBurger123]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

Right so if you press the power button Vs is totally dead ? Btw some of these sets you can turn the standby Led off so dont be fooled by that

[lamouche1]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

yes

[lamouche1]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

no clicks nothing except 5v standby

for now all the diodes and fets that I'ved check test ok

[dick_barton]

Re: 50 Samsung (Hp-t5054) Completely Dead PSU

Have you read through the following post.
https://www.badcaps.net/forum/showthread.php?t=21497