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TV Shows Image After Hours' Break, But Nothing When Turned Off And On

When powering on from being in the off-state for a few hours, my Samsung MU6470 123cm works fine. Picture is good, everything is normal. But when turned off and turned back on in a short period of time, nothing. No image. Just the backlight.

This seems like a very peculiar problem to me. Unfortunately, it's only the most recent in a slew of problems I've been having. In fact, I had dropped it off at a local service center because of the following issues just two days ago:

  1. Just one week after the warranty period ended, my TV started having this dark column on the left (close to the center) side of the screen. It happened with no warning. A suddenly present vertical patch of darkness, focused more towards the bottom (please look at the attached picture). I still had image, though, so I ignored this for a while.
  2. But then a few day ago, I turned my TV on and it just started flickering randomly. No image, just grey to black, random flicker. This is a video of that issue.

The service people were able to fix the first problem by replacing the LEDs. But after doing that they're now facing this "The TV needs a break if you want it to work" issue. They don't know / aren't sure if this is still Problem #2 mentioned above, just presenting differently because the LEDs have been fixed, or if it's a new problem entirely. But they seem to be implying it could be a problem with the panel itself, but that would cost me a bomb to replace. I really don't want to get ripped off / tricked into spending so much money unnecessarily, so I would love to have you guys’ insight.

Also, they described this problem to me over the phone. I'll try and get footage of it when I go there in about 6 hours.

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Hi,

Did they say if they tried a new power board?

Just wondering if as initially the LEDs were faulty, which looks about right from the image you posted then perhaps this may have also damaged the power board depending on the problem with the LEDs.

In the video not all the LEDs are coming on, just some.

Try the following:

Turn off the TV and then disconnect the power from the TV.

Remove the back cover from the TV and disconnect the cable between the mainboard and the power board.

Reconnect the power to the TV.

When the mainboard is disconnected from the power board and power is applied to the TV the power board is turned on to full power output.

The LED backlights should all turn on full and stay on. There will be no picture because the mainboard has been disconnected.

If the backlights don’t turn on and stay on then there is a problem with the power board or the LED array or the connection between the two.

Measure the voltage at the LED power connector on the power board. If it is >220V DC then there is a problem with the backlights (or the connection to the backlights as the power board is trying to drive the voltage as high as possible trying to turn them on. If it is <80V DC then there is a problem with the power board.

If the backlights stay on measure the voltages at the power board connector where the mainboard cable was connected. The voltage values should be printed on the power board near the connector. Check that they are as stated. If they are then there may be a problem with the mainboard.

Be safety aware if you decide to try this as there is exposed lethal AC voltage on the power board when the power is connected to the TV.

Do not work in the back of the TV when the power is connected if you don’t know what you’re doing.

Disconnect the power before working in the back of the TV unless you’re “live” testing and you know what you’re doing.

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In all the scenarios you posit, it doesn't seem like the panel itself could be the problem. You're saying it's either the power board or the main board, or some connection between the two, right?

Also, I'm wondering, does the fact that the TV DOES function when it has a few hours of rest/idling first, does that help in any way in determining where the problem could be?

- de

@t4akawolf

The tests were just a quick way to determine the most likely problem area first i.e. backlights, power board, mainboard.

The panel has nothing to do with the backlighting per se where there does seem to be a problem with the TV i.e. they are separate to the LCD panel and not internally integrated with it

The mainboard tells the power board to turn the backlighting on and off but in the test as above where the mainboard has no control of the power board as it is not connected to it if there is still a problem with the backlights you have eliminated the mainboard as the cause. You then have to work out whether it is the power board or the backlights or the connection in between

Once you get the backlighting sorted out as per the test above i.e. either it works every time - stays on, not blinking or off or it doesn't and if not why not, then you move on to the next problem i.e. is there a video display on the screen.

I couldn't hear any audio in the video so if it wasn't there either it is looking more like a mainboard problem, but then the power board also comes into play because it supplies the power not only to the backlights but obviously also to the mainboard.

The problem as described by you could be classed as intermittent (to a degree) and these are always difficult to find so all you can do is to eliminate each section one step at a time i.e. backlights OK, power supply voltage outputs OK, so power board assumed to be OK, also check voltage at mainboard and tcon board. Video output yes/no. If no and no audio then maybe mainboard, if no and audio OK then mainboard "maybe" OK, but then could also be cable to tcon board, tcon board itself, tcon board cable to panel or panel

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