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Please help! Need help Diagnosing/Troubleshooting TV! (Video included)


Yesterday my TV decided to stop working and I'm having trouble diagnosing the issue.

Here's a video of the issue:


The TV will work properly for around 30-60 seconds.

Then the sound will briefly slow down before the TV "crashes".

It stops responding to the remote (normally a light below the TV flashes when a remote command is received) and a whining noise can be heard at the rear.

After this happens, unplugging/replugging the TV in will cause the power LED to light, but there's no picture, sound or responses to button presses/remote.

Disconnection from power for 10 minutes or so is the only way to get it to show an image again, followed by the usual crash.

I've opened it up check cables and capacitors but all seems fine.


Due to the slowing of sound just before it crashes, I feel it may be a lack of sufficient power to the TV, either the fault of the external PSU or the power board in the TV itself.

This is simply based on how other devices react to low power though, I'm not an expert by any means!

If you have any ideas then please let me know!

I'd like to figure out the cause before I start randomly buying replacement parts in an attempt to repair it.


As requested, here are some pictures of the TV's boards.

Inverter board;

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Inverter board Caps:

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Side Main Board:

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Main Board:

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TV Overview:

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@hellsplumber what model is your TV? Sure looks like a component overheating. You do need to check the caps and IC's on the power supply as well as the main board.


@oldturkey03 Thanks for the reply!

The model is the Sony kdl-42w705b.

I ordered a replacement power supply which arrived today, but sadly I'm having the same issue so we can rule that out.

The problem takes under a minute to occur even after sitting overnight in a cold room. Is this still enough time for it to overheat?

I'll look into checking the caps properly.


@hellsplumber post some decent pictures of your boards with your question. That way we can see what you see and can possibly help you out more. Use this guide Adding images to an existing question for that


@oldturkey03 As requested I've added pictures of each board, hopefully they can be of use!


@hellsplumber did you replace the caps on the LED board? If so, for what reason? If not then they do look like they have been replaced.


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@oldturkey03 I thought you may be interested to hear what happened!

Trying to find/replace the defective part, I ordered a new mainboard from eBay in the hopes that replacing it would fix my issue.

But the board I received turned out to be from a different model (the 52" instead of 42").This turned out to be a blessing in disguise, as putting it into the TV prevented it from booting up normally, and it instead flashed an error LED indefinitely.

Under normal circumstances the TV would attempt to boot, then crash shortly afterwards.

As this happened so quickly, the TV wouldn't take commands from the remote.

Thanks to the wrong mainboard, the TV is able to take commands from the remote while it's in it's error mode! This allowed me to send the Factory Reset command (Hold UP on the remote while pressing the TV's power button). When I did this, the TV froze and required me to pull the power.

I put the correct mainboard back inside, and it refused to even turn on. I was sure I'd killed it for good.

But I left it disconnected from the power for a few hours, reconnected it and it FINALLY booted up, with it's settings completely reset.

Since then it's been on for about 24 hours instead of the usual 1 minute!

It did crash once, but instantly reset itself instead of the usual freeze. Googling around I found someone else with the restarting issue who recommended turning Wifi off, which I've now done.

I've had 0 issues since doing so and am happy to have my TV back :)

So after all that, it all seems to have been a software issue.

For anyone else with this issue, attempt a factory reset and disable Wifi!

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@hellsplumber the soldering of caps on the LD board look odd.Your LD board is a14STM4250AD and that is where I would start. Check the connector CN4001 against the image. On the image it is listed as 2001 but should be the same connections and voltages as your board. Let us know what you find.

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Update (01/17/2018)

@hellsplumber does this look like your TV's board layout? If not, any chance you can post an image of it with your question?

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Update (01/17/2018)

There should be a T-con board T420HVN06.2 somewhere

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I hadn't noticed the odd solder job on them until you pointed it out!

The TV was originally an "As New" refurb, so maybe there was a previous issue with the LED board that was solved by replacing the caps.

Due to the 10-30 second time before "crashing", I'd become convinced it was a fault with the capacitors (as it's in line with their expected charge time).

I may be talking nonsense(I'm far from a professional!) but due to this hunch I'd ordered a new LED board on Friday.

The discovery of the (possibly) previously replaced capacitors gives me hope that my hunch was correct.

We'll find out for sure soon as the new board should be arriving today or tomorrow. Once I've switched them out I'll post the results. Wish me luck!


@hellsplumber that appears to me like a sound idea. I'd do the same thing. Really hope it works out.


@oldturkey03 Thanks, and thankyou for all of your help during this time :)

I'll update once the board arrives.


@oldturkey03 The board just turned up.

After putting it in the tv it stayed on long enough to give me hope.

Then crushed all hope as soon as I dared believe it was fixed.

All I can offer is more details:

When the TV crashed, I noticed a whining, almost beeping sound from the LED board.

And after a while of leaving the TV in it's crashed state it turns off completely (no video,backlight,powerlight etc) and refuses to turn on without disconnecting it from the socket for a while.

Maybe this can help further diagnose it, because I'm all out of ideas and pretty down about the whole thing.


@hellsplumberdang sorry to hear that. Did you keep your old LED board? If the new LED board caused this to be worse than the component that over heated a bit before now overheats much quicker. Back to the drawing board. Let me check the manual and see if there is any other indication. It does start to look more and more like a power board issue......


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