Sceptre X322BV-HD burnt power supply

[Mr Bill]

Smoke actually rolled out the top of the tv .
The power board has a big burnt spot where the 2 plugs are for the ccfl bulbs. I've never encounter an issue like this before so where do i start? Is the board even repairable or should i just wait for a replacment to become available?

Thanks

[tom66]

Re: Sceptre X322BV-HD burnt power supply

Some kind of carbon residue may have built up and created a high resistance short circuit which led to rapid heating of the track.

Try cleaning the track, repairing it if necessary, then applying some kind of HV insulating silicone to it to prevent future arcing.

[Mr Bill]

Re: Sceptre X322BV-HD burnt power supply

Tom, i cleaned the carbon area with alcohal but it pretty much still looks like picture 3. It doesn't look like there is a trace that goes between the 2 points but i haven't picked at it with a pen knife yet. The high voltage silicone, where would this be bought at? Digikey or is there a specific brand/type that works well?

[tom66]

Re: Sceptre X322BV-HD burnt power supply

Ordinary insulating silicone will do. It looks like you should be able to test it without the silicone for now, then add the silicone to prevent a repeat of the problem.

[Mr Bill]

Re: Sceptre X322BV-HD burnt power supply

Here is a picture after i scraped the area. Would this be good enough to give a try or should i clean it better?

[Mr Bill]

Re: Sceptre X322BV-HD burnt power supply

Maybe there is a trace in there somewhere, it's reading 69.4 ohm. I just don't want to cook the board anymore than it already is.

[budm]

Re: Sceptre X322BV-HD burnt power supply

As you can see, they put the slots on the PCB to create air gap between the high voltage points, you need to competely cut out any carbonized section of the board out completely.

[Mr Bill]

Re: Sceptre X322BV-HD burnt power supply

Bud,
I drew a few cut lines. Would this work? or is there an easier way?

[budm]

Re: Sceptre X322BV-HD burnt power supply

That will do, you can also cut the board by follow the tip where the cutout is already there and cut it through. Take the resistance reading and fill the gap with Silicone RTV. We want the gap between the two points.

[Mr Bill]

Re: Sceptre X322BV-HD burnt power supply

Here is pic of the cut. I'm still getting the 69.4 ohm reading between points after i cut it.. Does this matter?

[retiredcaps]

Re: Sceptre X322BV-HD burnt power supply

Paceworldwide on youtube has an excellent series of soldering videos. They are old style narration, which I love, but highly relevant.

I watched them sometime last year, but they have a whole series on rework and repair.

See

http://www.youtube.com/user/paceworldwide/videos?view=0

PS. Your multimeter needs an external cleaning!

[budm]

Re: Sceptre X322BV-HD burnt power supply

You may have burnt out winding on the secondary side, I would take that transformer out and measure the resistance and compare it to the un-burnt one.

[Mr Bill]

Re: Sceptre X322BV-HD burnt power supply

I think i figured out where the 69.4 ohm reading was coming from. I put the board it and the backlights came on without any smoke or buzzing. Just need to apply some RTV silicone and close the tv up. Would the RTV silicone from an auto parts store work or should this be from an electronics outlet?

Retiredcaps,
what do you use to clean the meter? Alcohal and q-tips? I've had this meter for almost 12 years now and i've never even thought to clean it

Thanks

[retiredcaps]

Re: Sceptre X322BV-HD burnt power supply

Would the RTV silicone from an auto parts store work or should this be from an electronics outlet?

I used this in my current ATX power supply

http://www.permatex.com/products/aut...ve_Sealant.htm

They do have a high temperature version in red I believe. I think it was $3.99 at Home Depot Canada.

Retiredcaps,
what do you use to clean the meter? Alcohal and q-tips? I've had this meter for almost 12 years now and i've never even thought to clean it

For the outer case I use gojo or fast orange (hand cleaner with pumice). The yellow Fluke cases that I buy used sometimes are covered with dirt, grease, etc. Dirty multimeters don't attract the same number of bidders or a high price -> perfect for me.

For the body, I just use a damp rag

Everyone knows that a clean multimeter gives more precise readings!

[budm]

Re: Sceptre X322BV-HD burnt power supply

That Silicone RTV for making gasket is fine, I do not believe it contains any acid like the generic home Silicone sealant, I know the Silicone for electronics repair does not contain acid which is what I use at work on the PCB (it has to conform with UL) so it will not eat up the copper traces. So what did you find on the 68 Ohms reading? That is really low Ohm! Do you get the same reading on the other transformer?

http://www.hmcelectronics.com/produc...licones/RTV162

[Mr Bill]

Re: Sceptre X322BV-HD burnt power supply

I'm Going to have to re-visit this old thread. I gave the tv to a friend for a real world daily use and it died after about a week. The tv turns on but no backlight, not even a brief flash. We did confirm the tv is displaying a picture by shining a flashlight throught the lcd and saw the menu. I took the back off and checked the voltages coming from the power supply.

5v - 5.21
12v - 12.35
24v - 24.02
DM - 2.285
BK - 3.109

384v at the large cap with the tv on. So the power supply portion seems to be functioning correctly. I've tested the mosfets on the top of the board and the few surface mount ones on the bottom and they all test in circuit good (not shorted). I checked the 2 ballast caps where the PSU originally arced and the meter reads OL which i believe is correct.

I'm hoping somone might see the layout of this board and shine some light on what drives the 2 connectors that go to the panel. The 24v by the way goes to the main board not the panel directly.

The pictures in post number 1 aren't the best. Let me know if you want some quarter shots of the board.

Thanks

[budm]

Re: Sceptre X322BV-HD burnt power supply

We need to check the inverter section again, the power supply is putting out like it should. The inverter section uses the >300V for driving the inverter transformer.
Brighter pictures of the top side of the board? Four 1/4 section pictures of the bottom side?

[Mr Bill]

Re: Sceptre X322BV-HD burnt power supply

Sorry for the delay Bud, got the flu. Here are the pictures. I hope the resolution is good enough for troubleshooting. The bottom the board has a clear finish sprayed over it. Made taking a clear photo difficult with the flash.

[budm]

Re: Sceptre X322BV-HD burnt power supply

OK, I just download the pictures, let me trace things out.

[selldoor]

Re: Sceptre X322BV-HD burnt power supply

May just be the picture but U4 looks a bit singed?