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Help diagnosing faulty 55PUS6704.

Hi. I'm looking for some help from the community to diagnose the fault on my Philips TV please.

It started off with a darkish hazy horizontal band about 1/3 from the bottom of the screen. About a week later the screen went black (screen off, no backlight) after changing inputs. Input signal was working briefly before going off. Sound still worked, but eventually the sound also stopped working. Ambilight still works and changes colour in response to pressing menu buttons, etc. When powering on, the backlight briefly flashes for a split second then goes off.

I was suspecting TCON board but I'm not sure since there are issues with backlight and sound also. Tested voltage and it appears to be getting 12v, although I'm not entire sure where the board fuse is, so not sure if that is at fault.

Before I go and buy a replacement TCON board, I would greatly appreciate advice on additional things to check to diagnose the fault.

Thanks in advance!

UPDATE 1: Adding images of boards

Power board:

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Main board:

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TCon board:

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Update 2 - 03/09/2023

@oldturkey03 - here's some better pictures of the TCON board (hopefully)

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Update 3 - 03/09/2023

@oldturkey03 Right, good news (I think). Turns out the screen and sound are in fact working. Not quite sure how I missed it in my earlier tests (must have been on a bad input), but I managed to load up the YouTube app and with flashlight could confirm picture and sound.

So now I've further dismantled in an attempt to access the backlight LEDs. It was proving a bit tricky/noisy for tonight so have stopped and will continue again tomorrow. I did notice an odd smell when accessing the panels so I'm thinking perhaps one of the LED strips has burned out which would correlate with the dark shadow we saw on the screen before it failed completely. Challenge now is to figure out if it's the strips themselves or the driver / power supply. The backlight flashes on briefly when the TV powers up but I haven't yet confirmed if all of the strips light up, or just some of them.

UPDATE 4 - 04/09/2023

Backlight strips accessed and confirmed 2x LEDs not working across 2 separate strips when testing with multimeter diode tester. So now to decide whether to replace both strips, or just the 2 LEDs.

@oldturkey03 - Any thoughts on how easy it is to replace individual LEDs and where to source replacement LEDs or strips? Anything else to check before replacing?

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Good evening,

A gradual failure...almost sounds to me like something within the system has died. I would try and find the fuse by purging through the internet and finding the manual/schematics. Alternatively, you could try and power on and see if anything gets hot. That indicates a short.

You seem like you know what you are doing so i reckon you're on to something. But good luck mate :)

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Thanks for the quick reply. Will try and dig out some schematics and see where I get to.

I suppose I was wondering if there's any more definitive tests I can do to rule out issues with the power and main boards, as it looks like the TCON boards can be replaced pretty cheaply if I can be confident that's where the issues lies.

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Gee, definitive tests are hard to come by because it an vary. One would be to plug power in and see what gets hot. That would indicate a short.

I guess another one could be to check continuity across the board as based on the fact it sits in a TV, i would assume the trace paths would be visible, like it would be on a game console.

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Thanks. Really appreciate the advice. I found a picture that confirms the TCON fuse location so I will retest that tomorrow and see where I get to and report back

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@scifi76 this "darkish hazy horizontal band about 1/3 from the bottom of the screen." is not typical of a bad T-con board. Nor is a blown fuse. When any fuse blows, you get an all or nothing responds. Fuse blows = nothing works. The failure on your TV escalated over time and that is not typical of a bad fuse.

For now, I would suggest that you do not change anything. It can get expensive to replace a board that does not need to be replaced. We need to see your boards to find where some of the test points are. Post a pictures of the individual board as well as one that shows the complete setup of the back of your TV (cover off of course ;-)

I am not saying it is or it isn't the T-con board. It is just very unlikely to be the (only) issue. It could be the power board (unlikely) or the main board, Ribbon cables (check for tears and corrosion) and lastly the panel. Let's check it out and see if we can narrow it down.

Adding images to an existing question

BTW Philips is a bit of a PITA because their manuals etc. go by chassis number. The 55PUS6704 should actually be a 55PUS6704/12 and the chassis is a TPM19.6E LA

Update (09/02/23)

@scifi76 nothing obvious on the boards but some new , more focused images will definitely help. Here is a T-con board and just pointing to some of the test points we'll need to check on yours. There are some on the right side of the image that I cannot make out :-)

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Update (09/03/23)

@scifi76 to check those test points, you have to reassemble your TV. Then turn it on. Using a multimeter, set it to VDC at a ~30V range. Black wire goes to ground. I usually use a screw head somewhere on the metal backing of the panel. Then use the Red probe to test the individual test points. Let us know what results you get from it. Since your TV is on, remember not touch anything with your bare hands. Stay away from the power board too since it will carry some decent current. It'll sting quite a bit when you make contact :-)

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Check the fuse for voltage on both ends. That way we know it is working and don't have to switch your meter to continuity or Ohm mode.

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Thanks for this, I think you're right, I'd feel much better buying replacement parts if I was sure what was at fault, but currently I'm not. I need to narrow it down.

I've added some pictures of the boards if that helps at all. They're not the best pictures so I'll add more tomorrow when I'm back home.

I already removed and reseated all the ribbon cables and couldn't see any obvious signs of damage.

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Thanks for the quick response and thorough advice. Below are the test point measurements:

Fuse: 11.8v both sides

VDDINI: 11.8v

VGL: 9.9v

SCL_T1: 3.2v

SDA_T1: 3.2v

VDD_2V1: 1.1v

VGL_1: -8.3v

LS_SCL: 3.2v

LS_SDA: 3.2v

AVDD: 17.6v

SDA: 3.2v

VDD1: 8.3v

VCOM: 7.2v

I managed to get hold of the service manual. Out of interest, would I expect to find the test point voltage ranges in there?

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@scifi76 nope! That would be to easy. Not sure which service manual you got but most of the once I have do not even show test voltages on the main board not do they have proper pinouts etc.

The T-con board is a BOE so they would have the schematics etc. but those companies just do not want us to have any information of that. Remembr, they do not like repairs. They want you to buy a new TV, not repair your "old" one. They want us to continue to feed the Profit-before-People (Planet) machinery. I work hard for my money and refuse to continue to give it away. Hence, I repair, repurpose and try to help others do the same. Sorry got carried away here. Back to your TV

The voltages on the T-con board check out okay. Check your manual. See if it has something about firmware update. Philips is kind of weird with theirs and some odd errors can happen with bad firmware. Try to reinstall that.

Prime suspect is now the main board, due to the no audio issue combined with the other issues.

Measure the voltages to your backlight LED's when the TV is on. It is VDC but set your meter to about 300V and let the probes do the touching. Hands off please.

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@oldturkey03 I totally agree with your profit before people sentiment. I hate to contribute to the whole throwaway culture, so I'm taking this as a personal challenge to try and get working again. Plus it wasn't "that" old so I begrudge just letting it go in the skip. I work in IT so have a hard time letting it go that without trying :-) Really appreciate all your efforts to help me with this.

I'll have a read of the manual for firmware but I personally think it's unlikely since the fw updates were always manual and it hasn't had an update installed for quite some time (at least several months prior to any of the failure symptoms). Reinstall might be tricky without the screen unless there's a mode to install from usb on boot up - will do some research.

You're right about the service manual. It doesn't appear to show any of the test points or voltages. At least not to my untrained eye. Do you have any idea what to look for on the main board?

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@scifi76 not of hand but ;et me see what I can find out based on the actual board number. I see it has a big heatsink on there but can you "feel" if the processor may get excessively hot? I wonder if a quick heatgun reflow may resolve some of that. Do you have one of those in your garage, basement, storage room (wherever it is you store your tools)?

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scifi76 will be eternally grateful.
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