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Repair and disassembly information for the Samsung 55" UHD television with model numbers UN55MU6290xxxx. Released in 2017.

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Power supply fuse keeps blowing

Hello,

We have a 4 year old UN55MU6290 Samsung TV. Last week while it was on it made a pop sound and turn off. Once I had a bit of time over the weekend I opened it up to have a look.

First I did a visual inspection and didn’t find any component damaged or burnt (neither on the power supply nor on the main board). I took a multimeter and first thing I checked the fuse: open circuite.

I thought easy enough… I ordered a package of matching fuses (T5AH250V). The fuses arrived today. I replaced the fuse reassembled the TV plugged it in and… it didn’t work.

I open up the TV again checked again the fuse I had just installed and… it had blown.

I then replaced the fuse again. This time I did not reconnect the neither main board nor the backlight to power supply board and I powered it up with the TV open.

The fuse blow again as soon as I plugged in the power. So for sure there is something wrong with the power supply board. It burns the fuse as soon as powered up even if disconnected from the rest of the TV.

Now I can order a new power supply board (BN44-00807K) for cheap. The question now is how can I check that there is nothing wrong with the backlight or the main board that cause the damage to the power supply board and will damage the new power supply board the same way?

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Hello all,

I bought and installed the replacement power supply board.

Now when I try to turn on the TV the audio start, but the screen is completely black…

I guess it could be the main board, the back light the LCD itself or a combination… Any idea how I could troubleshoot this?

Is it even worth to try to resuscitate this TV?

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@jostosalis the backlight shortened out will not pop the power fuse. It will just not come on. Same with the moain board. There is no connection coming from the main board to the power board, that would cause the fuse on the Hot side of the power board to fail. This sounds like a bad power board component.

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@oldturkey03 thank you for your prompt feedback. So even if the backlight is shorten or there is indeed an issue with the main board these should not cause the new power board to fail?

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@jostosalis I have not had the main board, or any other board, shorten out the fuse on the power supply. It has always been the power board components itself that caused this. If the LED's would be short it would not cause issues with the power board. Check all the diodes that are on that part of the circuit, The short is usually on the hot side or on one of the power regulators on the board. If this would be my TV, I would get a new power board :-) (or try to find the schematic and attempt to fix it)

If unsure about it, just unplug the main board (Samsung tests their power supply like that) and then plug your TV in. See what happens.

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@jostosalis now test your backlights. Disconnect the power cord on the power supply. Disconnect the cable from the main board to the power supply. Plug the power cord back in. your backlights should come on. No, not the screen or any sound. Just the backlight. You can see those through the many openings in the sheet metal on the back of the LCD panel. Post some images of all of your boards with your question. Use this guide Adding images to an existing question for that so we can see what you see.

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Hello,

I tried as suggested to unplug the main board from the power supply and then power up the TV. The backlights did not turn on.

I also measured the following voltages at the check points:

- Main board connected, TV in standby 12.79v / 180.1v

- Main board connected, TV on (audio is running) 12.77v / 185.5v

- Main board disconnected 12.80v / 171.8v

These values seem to be a bit off from the regency values printed on the board (11.8v / 210v). Is there any way to check if the issue are the backlights or if the new power suppply board is defective as the values are off?

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@jostosalis the 210V listed on your board would be the max. So backlight at 100% etc. 185V will definitely work. Sounds like your power board is supplying proper voltages.

Does your TV have a separate T-con board or is it integrated on the main board?

Turn the TV to a station where you can hear the sound. Next, use a flashlight and shine the beam at an angle against the screen. See if you can make out shadows or shapes.

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