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Old 04-19-2018, 07:30 PM   #1
DXseekerMO
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Default Samsung UH50EH5300FXZA, help with a transformer?

About 2 months ago I got a Samsung UH50EH5300FXZA that was a lightning strike victim. I'm finally getting around to looking at it.

The AC fuse was blown. I checked the board for a direct short and didn't find one so I piggybacked a fuse on top of the blown one, plugged it in, saw sparks inside this transformer and the fuse blew.

This transformer reads shorted corner to corner. There's a number on it, but a Go-ogle search comes up with nothing. I was wondering if anyone can help me make heads or tails out of this number so I can source a replacement?

I'd take one off another board if I had a way to spec. this one out and match it.
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Old 04-19-2018, 07:51 PM   #2
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Default Re: Samsung UH50EH5300FXZA, help with a transformer?

1) That is an inductor for the active PFC Voltage booster circuit.
2) You are reading the DCR (DC Resistance) of the inductor which will show very low resistance, you can only test for open circuit with simple Ohm meter, you need ringer tester (for shorted turn test), inductor tester to read inductance.
3) Since it blow the fuse then you need to test the bridge rectifer, diode, MOSFET (especially the one for the PFC circuit). So start checking the semiconductor devices for low resistance first.
4) What is the P/N of this power supply board? BN44-?????
5) Need to upload good clear straight shot pictures of the whole top and bottom side of the board, the pictures must be clear enough to read the printed texts and able to see the traces.
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Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956

Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999

Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl

Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/

TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809

Last edited by budm; 04-19-2018 at 08:04 PM..
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Old 04-19-2018, 09:15 PM   #3
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Default Re: Samsung UH50EH5300FXZA, help with a transformer?

Board number BN44-00668A, here's the pix
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Old 04-19-2018, 09:18 PM   #4
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Default Re: Samsung UH50EH5300FXZA, help with a transformer?

That inductor had sparks in it when I plugged it in, of this I am 100% sure. The fuse also looks like it had identical looking sparks inside after plug in. Does that sound like a shorted turn in there?
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Old 04-19-2018, 09:36 PM   #5
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Default Re: Samsung UH50EH5300FXZA, help with a transformer?

Did you test the MOSFETS, the Diodes as suggested first?
The only way to get too much current flowing is the shorted PFC MOSFET.

Last edited by budm; 04-19-2018 at 09:38 PM..
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Old 04-19-2018, 09:52 PM   #6
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Default Re: Samsung UH50EH5300FXZA, help with a transformer?

Not yet, I've been listening to news about the KOZK TV tower collapse in Fordland MO on TV. That tower is 11mi. from my house. I heard it collapse.
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Old Yesterday, 03:14 PM   #7
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Default Re: Samsung UH50EH5300FXZA, help with a transformer?

Quote:
Originally Posted by budm View Post
Did you test the MOSFETS, the Diodes as suggested first?
The only way to get too much current flowing is the shorted PFC MOSFET.
Holy old thread revival Batman!

So I finally decided to break this set back out and give it another go. Before I put it up I installed MOSFETS QM801CS and QM802CS. End result, fuse doesn’t blow but TV will not turn on and voltages at A5V and PS_on were very unstable.

Here are the voltages from this go-around, the first row of voltages is the PSU plugged in to the main board and the second is unplugged from the main board.

1 B13V…………………0…………………… .6 to 4.2V unstable
2 PDIM………………..0……………………. unknown/0v
3 B13V…………………0…………………… .6 to 4.2V unstable
4 B13V…………………0…………………… unknown/0v
5 Vamp………………..0………………….. .6 to 4.2V unstable
6 BLU_on…………….0…………………... unknown/0v
7 Vamp………………..0………………….. .6 to 4.2V/unstable
8, 9, 10 (gnd)……….Continuity present
11 B5V…………………0…………………… unknown/0v
12 A5V……1.8 to 4.4 unstable…….. unknown/0v
13 B5V…………………0………………….. unknown/0v
14 PS_on… .1 to 2.3 unstable**… unknown/0v

** Mainly stays low with quick flashes to upper voltage listed

The reason many of the even numbered pins are “unknown/0v” is because by the time I got around to checking them power readings had mostly disappeared from the terminals, including the ones I was fast enough to get readings on.

Furthermore I’m getting unstable voltages on both the hot and cold sides of the PSU, but the rectifier diode output is a solid 165V and so is the voltage at the main cap and drain pin of MOSFETS QM801CS, about 24V solid on the drain pin of QM802CS

I tried changing transistors QM807 and 808 which are EPITAXIAL PLANAR PNP TRANSISTOR and is described as a VOLTAGE REGULATOR, RELAY, LAMP DRIVER, INDUSTRIAL USE because the voltage at the emitter of QM808 was an unstable 1.8 to 4.4v. The base pin voltage was 10.1v solid and there was no voltage on the collector. I changed them because they are noted as commonly failing components. After this I re-flowed out any bad solder joints.

Unfortunately the problem still exists and appears to be getting worse, in the sense that the voltages are now almost all the way gone. So does anyone have an idea what may have crapped out here? I can’t seem to find a schematic for this board, BN44-00668A. Does anyone happen to have a schematic laying around for this?

Good clear expandable pictures included!
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Old Today, 09:53 AM   #8
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Default Re: Samsung UH50EH5300FXZA, help with a transformer?

Check the 16-pin SOIC (ICM801S) located on bottom of board near QM801CS and QM802CS. It is an LED driver IC.

Your first photo looks like there is a scorch mark on it, and I can't tell anything from the second photo.

I had a UN46EH5000F TV with a similar power supply design that would turn on, but the backlight was strobing about once a second. This IC was screwed on my TV, with evidence of a round hole burnt/melted in the plastic.

The IC was shot, but even after replacing the power supply, about 20 out of 44 backlight LEDs were burned out as well...


Incidentally, there is a repair kit from shopjimmy for less than $10 for this board with that IC included and a whole bunch of other parts.

http://www.shopjimmy.com/samsung-bn4...repair-kit.htm
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