Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

[tom66]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

For now it's not needed.

[dailafing]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

ok, so im about to disconnect both of the marked VS...

Not monitoring any voltages so meter is off...

What am I looking for here, what are the different outcomes of this test?

[tom66]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

If Vs rises to 205V or thereabouts, you have a shorted X- or Y-main board.
If it doesn't, you have a bad power board.

[dailafing]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

Ah, so I need to continue monitoring the VS-TP?

[tom66]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

Yes.

[dailafing]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

ok, done... No voltage reading at all like when VS&VA are plugged in...

So from what your saying, and by deduction, it so far appears to be the powersupply?

One thing I noticed this time around was the stand-by light was blue down the bottom? I hadn't noticed it there before, but then I've not ben looking for it...

Does the presence of a solid blue/white light mean anything substantial? I mean, its gotta be getting power from somewhere?

Also, the DMM seemed to show minus symbol on the cycle restart? intermittently...

http://youtu.be/t_CDTnoSod4

[tom66]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

This is exactly the same thing my 50" PSU was doing and it had some short in the Vs tract of the power board. Specifically the two largest FETs (TO-252) mounted to the heatsink.

Have you double checked this fuse is intact?

The light is active in standby mode; the standby portion of the power supply is separate from the main part.

[dailafing]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

Yeah, I had both of them out earlier on, and did an ohm test, they were reading 2-5 ohms... and the DMM sounded a beep to show that it was a circuit.

[tom66]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

OK, one further thing to test. Do you see the point marked VG? This should measure 14V to 16V when the TV clicks on.

[nogger]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

I do quite a lot of these boards & looking at your scan of the underside of the PCB you have some very poor soldering on the mosfets (VA Tract) ZDX801 /802
I would imagine that this is the cause of your problem. You will not get ANY VA or 5v,12v or any other voltages apart from the STBY 5v. (forget about VS for now)

Easiest way to repair these boards is to measure across the MOSFETS (Gate-Source) & you should read 11 ohms , if you don't then your Mosfet's have most likely blown & taken out the small surface mount resistors & diodes next to them. It's also possible the chip on the little daughter board & some diodes have blown as well.

Measure the MOSFETS with the board on the bench & advise us of the reading, while you have it on the bench take a good magnifier & have a look at the soldering on the MOSET pins. I can see from the image that it's not good but i do a lot of them as i said, you may need a magnifier to really highlight the problem.

You have to work to get the VA tract working first as without that you will not get any secondary voltages. The VS tract (if the fuse is intact) is most likely not at fault & can be tested later after the VA is up & running.

Graham

[dailafing]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

OK, one further thing to test. Do you see the point marked VG? This should measure 14V to 16V when the TV clicks on.

Cant seem to find VG? can you circle on a pic? or say where to find?

Nogger, I think your post contains a lot of useful stuff.
I thought that the soldering looked ok compared to the videos I've seen while researching all this, from a n00bs perspective though.
Once I've tested this VG, and if tom has nothing more to add, i'll pop the board back off and do some hi res pics of the back....

Also, advice on if I should short the 400v caps before handling?

[tom66]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

Vg is on the same tract as the Va (linear regulated from 18Vamp.) Should be active as soon as you get a click. Vs is on a separate tract. Vg is on one of the connectors going to Y-main and X-main.

I've only done one of these so will refer to Nogger's experience. If you don't see Vs, it could just be because the lower voltages aren't coming up yet and the power supply controller is shutting the power supply down.

[dailafing]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

I do quite a lot of these boards & looking at your scan of the underside of the PCB you have some very poor soldering on the mosfets (VA Tract) ZDX801 /802

Could you highlight these points for me and post the image back?
I've just had a look now at the image, and really cannot for the life of me tell what the 801 or 802 points are? You must have magic eyes

Easiest way to repair these boards is to measure across the MOSFETS (Gate-Source) & you should read 11 ohms

How do I measure in the way that you describe; I'm unfamiliar with FET's and don't understand how they work. I think im right in saying they are like a voltage varied resistor?.
I guess from what you've said they are daisy-chained that allows me to measure them in some way?

If you don't then your Mosfet's have most likely blown & taken out the small surface mount resistors & diodes next to them. It's also possible the chip on the little daughter board & some diodes have blown as well.

From that, it sounds like a nasty repair job?

Measure the MOSFETS with the board on the bench & advise us of the reading, while you have it on the bench take a good magnifier & have a look at the soldering on the MOSET pins. I can see from the image that it's not good but i do a lot of them as i said, you may need a magnifier to really highlight the problem.

Could all this be simply the solder joints? I'm pretty good with soldering...

You have to work to get the VA tract working first as without that you will not get any secondary voltages. The VS tract (if the fuse is intact) is most likely not at fault & can be tested later after the VA is up & running.

I followed up to this part, but talking about the VA tract, then the VS tract... could there be more than one issue then? and could fixing one without the other cause the first fixed to fail, as most likely the original fault?

I know theres a lot to ask here, but I'm enjoying the learning experience, and I'm glad to see theres still an industry for this sort of think. With the introduction of LCD's I thought the TV repair shop died with it. which made me a bit sad.

Any way...

[dailafing]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

Vg is on the same tract as the Va (linear regulated from 18Vamp.) Should be active as soon as you get a click. Vs is on a separate tract. Vg is on one of the connectors going to Y-main and X-main.

I've only done one of these so will refer to Nogger's experience. If you don't see Vs, it could just be because the lower voltages aren't coming up yet and the power supply controller is shutting the power supply down.

Can you see it in any of your pics, or my ones? Im really checking everything here, just cant see it? will it be a little metal tube like the VS-TP & VA-TP?

if not, whats it look like?

[tom66]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

It's labelled right next to the connector which goes off to the Y-main board. In very tiny print.
There's also a little pressed in dome with Vg marked right next to it.

[dailafing]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

It's labelled right next to the connector which goes off to the Y-main board. In very tiny print.
There's also a little pressed in dome with Vg marked right next to it.

Got it... About to test it... Bit scary because im gonna have to be hands on with it...

[tom66]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

You can stick your probe into the Vg pin like you did for Vs?

[nogger]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

See the mmodified image. The RED circled points are the Va FETS, , check the soldering around the 3 pins on both transistors, its dodgy to say the least . You should read 11 ohms across the 2 outer pins

I have highlighted the Vs MOSFETS in BLUE, you should also get 11 ohms across the 2 outside pins on these as well.

Check them & let me know

[dailafing]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

ok done the VG...

I had left the meter to begin with on the 500v setting, so im guessing this was wrong, but not harmful?
I tested at each interval of the meter, and it appeared as though I was moving the decimal point, or changing the resolution/scope of the meter test...

I'm uploading a video of my findings now incase I've totally misread what's going on here...

and as I write this, I see that Tom has just said that I can stick my probe in like I did for the VS pin. Well, i'll include a pic here of what I was touching and it is not a petruding rod like VS/VA, but rather a flat solder point.... I'm worried I just measured the wrong thing here now... lol

Let me know if I did it right

Video: https://www.youtube.com/watch?v=-pMCo4pyzV0

Pic of VG point:

[nogger]

Re: Power Supply Failed - Samsung Plasma PS-42Q96HD (BN44-00162A, PSPF531801A, W2A)

The Vg will come back when you get the Va working properly.
Va is key to everything else, without it you get nothing (except clicking :-) )