Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

[djtom]

Hi all,
Currently working on a huge 63" Samsung plasma. Symptoms as follows - as soon as power is applied, the relay on the PSU board clicks and the blue power light comes on. 2-3 seconds later, relay clicks again, light goes off. Repeat ad infinitum. Tried disconnecting y-sus, same symptoms. Tried disconnecting y-sus AND x-sus, same symptom.

Can't see any obviously bad caps on the PSU board or any blown FETs. There are a couple of bulging caps on the y-sus board (huge 680uF 350v ones!) but otherwise all looks ok.

Va comes on and sits at 65v during the 2 secs that the board is energised. Vs and Ve don't come up though, both reading 0.3v or thereabouts. Vsc also absent.

Any ideas?

[ReeceyBurger123]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

Checked fuses on Psu ?

[djtom]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

Yep, all fuses that I can see check out ok. Both main incoming fuses, 3 x 20mm fuses and a ceramic are all that I can see and they all test ok.

[djtom]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

Getting a bit stumped on this one now. Can't see any dry joints on the board anywhere, nor any obviously fried components. Fairly convinced that it is the PSU board at fault, as it clicks in and out with nothing but the control board attached.
Anyone got any ideas as to where to start looking to narrow things down?

[djtom]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

Ok, time for an update on this thread.

I've disconnected everything from the PSU and powered it up. Nothing happens, which is to be expected. Connected a 22ohm resistor to ps-on and took it to ground, at which point the PSU clicked on, stayed on for 2 seconds then clicked off and stayed off. Va comes up to 65v then turns off again.

Did the same again but this time also shorting vs-on to 5.3v with another resistor. Same thing happens - on for 2 sec then goes off and stays off. This time all voltages came up pretty much as per the spec: 65v for Va (ok), -185v for Vsc (ok), 121v for Ve (should be 120v -close enough?).
The only one that seemed odd was Vs - the meter was struggling to keep up but it climbs rapidly and hits 210v (should be 205v) before the PSU shuts off. Could that be what causes the shutdown?

Any clues as to how to further test the board?

[Andrew F. Ali]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

You need to load the VS Output. Put two 100W 120Vac incandescent light bulbs in series and use this as a dummy load. If PSU is good light bulbs will stay on any flicker or dimming means PSU bad. Of course all jacks except the ac plug is disconnected from the PSU when testing. Post clear pics of the back side of PSU showing jack going to Main Bd and I may be able to help further.

[djtom]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

Thank you Andrew. I loaded Vs as you described with 100w bulbs, disconnected everything except the AC input, shorted PSon to gnd and VsOn to 5.3v with 22ohm resistors as before.

On switch-on, everything acted as it did without the load. Relay clicked on, bulbs came on brightly, then after 2 seconds the relay clicked off and it shut itself down again. The only difference this time is that when you remove and reapply the power, it stays dead unless you leave it unpowered for 15-20 seconds before trying again.

I've taken some close ups of the bottom of the board around the connector to the main board. I'd already tried to reflow anything that looked suspicious an had replaced some of the electrolytics with spares that I had lying around, hence soldering looking a bit messy!

The board is a bn96-003637a, also labelled as PSPF771F01A

Thanks!

[Andrew F. Ali]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

I think you did everything correctly.
Either a capacitor needs to discharge or a semi-conductor needs to cool down before another start-up. When it shuts down are you still getting the Std-by 5.3Vdc or does it disappear? If it disappears look at the PFC circuit but if it remains follow the VS-ON tracing and see where it goes.

[djtom]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

I'm pretty sure that the fault must be on the LV side of the PSU. I've tested all of the LV supply voltages both with and without VSon jumpered, and the same happens whether the HV side is energised or not.

Stby sits happily at 5v throughout, before PsOn is grounded, whilst it is grounded, and after the relay has clicked off again after 2 sec of operation. No change throughout.

All other voltages (12v, 18v, 5.3v) go from 0v to their respective correct values as soon as PsOn is grounded, then go back to zero after 2 sec when the relay clicks off.

PsOn starts at 4v, drops to 0.4v when grounded through a resistor, then stays at 0.4v even after the relay has clicked off until I break the connection to gnd when it jumps back up to 4v as expected.

These samsungs take PsOn low to turn on, but pull VSon high (using the 5.3v line) to turn on the higher voltages. As far as I can tell the fault can't be on the VSon line as the issue is the same whether that is pulled high or not. The fault must be on the low voltage side, but stby and PsOn voltages are present and correct even after the PSU has turned itself off. What else can cause the relay to de-energise after 2 secs?

I think that my next plan will be to try to trace the LV circuits back across the board. Without a schematic, this won't be easy! Any ideas / suggestions as to what to try next?

[djtom]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

Currently struggling to follow the PsOn lines across the board. It seems to switch two transistors but I'm getting confused trying to follow it after that. Any idea where I can find a schematic for it?
It's from a Samsung PS64P76FDX tv, and the board is a BN96-03736A, also labelled as PSPF771F01A.

According to shopjimmy the board is also used in the FP-T6374, unfortunately I can't find a service manual for that either! I've tried elektrotanya and various Google searches. Any ideas for what to try next?

[djtom]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

Stranger and stranger! IT WORKS! (Sort of)

I was probing around on the PSU checking voltages and trying to trace the PsOn circuit across the board when noticed that there was one place that when I measured the voltage, the relay stopped clicking and stayed on! No idea why - it is not a dry joint or a physical contact issue, so I can only assume that the minuscule capacitance or resistance of the DVM must be making the difference between switching a transistor (or not).

The magic spot is one of the legs of an opto-isolator, on the switched (higher voltage) side.

I reassembled all of the boards and plugged it in. click click click. As soon as the DVM probe touched the opto isolator leg, the set came on and I was able to scroll through menus, change channel etc.

Now I need to try to work out what the hell is going on, as it's hard to watch a tv when you're standing behind it holding a DVM probe in place. Any guesses? Bad transistor? Capacitor? Out of spec resistor?

Feeling more positive about this - amazing how seeing the screen light up can motivate you!

[Agent24]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

Might be a bad connection where the optoisolator's leg enters the body, or just a faulty part.

Replace the optoisolator, if that doesn't fix it, check\replace the parts it's connected to.

Can you upload a photo of the part of the board in question?

[djtom]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

Dragging this one back up to the top again after leaving it in the garage for a month or two!

I have tried replacing the opto-isolator - no luck, it does exactly the same. There's something very odd going on, as the set behaves normally whenever I am probing the voltage on the dc side of the opto. Somehow the voltmeter probe is causing a transistor or IC to stay switched on. This still happens even if the other leg of the DVM is waving around in the air!

I'm wondering if one of the small ceramic (poly? not sure, they're orange and squareish with rounded corners) caps is below spec and the tiny amount of additional capacitance in the DVM could be temporarily sorting the problem?

Any ideas? Pics of the board in question to follow later.

[Agent24]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

No idea, specifically. Added capacitance maybe a cause. Maybe a component is open and your meter is helping load down (or pull up?) a floating connection. I don't know.

If the Optoisolator wasn't the problem, I would suggest you try replacing\checking every component directly electrically connected to the lead you were probing, for a start.

Maybe try to draw up or find a schematic - it could help.

It could be something further down the track.. noise on the supply rail for that portion of the circuit. Maybe a failed decoupling capacitor and your meter is acting as a decoupling capacitor instead!

[Electronic Handyman]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

From your pics I can see that that PSU has some bad connections.I think whats happening is when the soldered connected hits certain temps the set will work but when it gets too hot etc the set shuts. I've seen this with more then one Samsung.I'd strongly suggest that if you've the time and patience go over all the soldering connections, especially at the hot spots.If you look on the left of the psu you can see cold soldering connections, remove the old solder and re-solder them.I personally go over the whole board and try to solder every soldering connection I find.Takes time but it makes the sets usually work better and last longer too.

This is again just my opinion but that set is a few yrs old and is bound to have bad caps, I'd replace all the caps located near the hot spots on the PSU and if you've bulging caps on the y-sustain board change those.Use good quality capacitors that are Low ESR. I'd also check all it's soldering connections and re-solder especially the hot spots.Remember to replace all the big caps on that board.

Note since you mentioned something regarding the set suddenly working after doing so trouble shooting that again tells me bad caps and bad soldering connections.

[littleted]

Re: Samsung Plasma PS63p76FD power cycling / relay clicking - PSU board?

Hi, I have this same set with same exact symptoms , I'm just wandering if you managed to get to the bottom of it?, any help would be greatly appreciated as I'm stumped, thank you in advance