Samsung UN55HU8550F - No picture, No sound

[KYBOSH]

Re: Samsung UN55HU8550F - No picture, No sound

another there, I might have grabbed that one if I didnt already have one: https://www.ebay.com/itm/20266077752...Bk9SR6T1htCzYQ

Thank you for the link! I put an offer in. Lets see if its accepted.

I have to is tv and the tcon went bad on it. Sometimes that fan doesn't work properly and it overheats. There is a heat sink silicon pad for the tcon also. Make sure that there since the previous owner has messed with it.

That will cause it to overheat also.

Though my backlights don't look that bad. If you unplug the main board from the power board and plug tv in that will let you know is if the backlights are good or not though. Lastly I didn't have issues with the buttons/ remote either.

I saw the pad on the tcon. Thank you for the note. If the previous owner had removed it i would have never know.

The fan seems pretty pedestrian IMO. Might have to uograde it to something that moves more CFMs.

Im still in need of assistance diagnosising if this is a firmware or bios issue. From my limited reading it looks like it but how would i go about rectifying it?

[KYBOSH]

Re: Samsung UN55HU8550F - No picture, No sound

So after talking to buddy of mine about the issue and watching a few YouTube videos I've come to the conclusion that the issue with this TV stems from bad LED backlights. The clicking of the power supply (which i have rarely come across), the fact that the TV booted properly a few times and how really bad the backlights look when they are ON lends validity to this conclusion i think. I will order a new set and install them. What puzzles me is the lack of responsiveness to input commands from either the remote or the on board joystick. But that maybe the nature of the beast.

[Storyteller12]

Re: Samsung UN55HU8550F - No picture, No sound

Did you unplug the main board from the power board and plug the tv in? Do this first. If the power board is good and the backlights are good they will light up and stay on until you unplug the tv again. If there bad the lights won’t stay on

It’s a quick test to verify if there bad or not

[KYBOSH]

Re: Samsung UN55HU8550F - No picture, No sound

Did you unplug the main board from the power board and plug the tv in? Do this first. If the power board is good and the backlights are good they will light up and stay on until you unplug the tv again. If there bad the lights won't stay on

It's a quick test to verify if there bad or not

Ive dine this and the backlights came on and stayed on before i continued on with other troubleshooting steps. I cant say i left them on for a long time though. How should i keep the TV and backlights on before they turn themselves off due to failure?

If you notice the photos of the backlights you can see large potions of unlit LEDs.

[Storyteller12]

Re: Samsung UN55HU8550F - No picture, No sound

Then Your backlights aren’t necessarily bad/ what’s causing your issues. It’s mainboard related I believe.

[nomoresonys]

Re: Samsung UN55HU8550F - No picture, No sound

it is a strange symptom, the lights did stay on when cable off tested but the clicking more than twice made me suspect issue might be before the mainboard.

[KYBOSH]

Re: Samsung UN55HU8550F - No picture, No sound

Then Your backlights aren't necessarily bad/ what's causing your issues. It's mainboard related I believe.

So, from what I understand, when a certain number of LEDs die it drops the current below a level which the mainboard doesn't like which then sends it into protection mode.

I will check the power supply (which I haven't done yet).

[KYBOSH]

Re: Samsung UN55HU8550F - No picture, No sound

it is a strange symptom, the lights did stay on when cable off tested but the clicking more than twice made me suspect issue might be before the mainboard.

I will check it again today to see if its stays on for an extended period of time just to be sure.

[KYBOSH]

Re: Samsung UN55HU8550F - No picture, No sound

Got my replacement backlights in the mail this weekend.
Will install them in a few days.

In case anyone is looking for it here is the Service Manuals for this model.
I wasn't able to find the specific manual for the 55" HU8550 but I found the manual for the 85" version. I also found the complete manual for the HU7500 which shares the same chassis (U8GA).

[KYBOSH]

Re: Samsung UN55HU8550F - No picture, No sound

Well I had a restless night so decided to change out the backlight.
Everything went smoothly and the backlights DEFINITELY look better than it did before but the TV is still exhibiting the same bootloop/restart/reboot behavior.

The t-con has 4 flex cables going to the LCD panel boards and I may remove them 1x1 to see if that makes any difference but Im starting to think this is a EEPROM/firmware issue to at the very least something to do with the mainboard.

I am reading a lot of ppl having success using a programmer to get themselves out of similar situations. I will have to look into this seriously.

Edit to add:
I believe I have found my EEPROM chip.
Its a W25Q128FVIG. I will try to read it tomorrow with my programmer and see if someone can help me with a good file.

[nomoresonys]

Re: Samsung UN55HU8550F - No picture, No sound

pretty sure that the powerboard should not be clicking repeatedly with the mainboard unhooked or with mainboard and or backlights unhooked, that's what makes me think there may be a powerboard issue, did you look over all the solder joints closely, examples of bad joints: https://www.google.com/search?q=bad+...ih=607&dpr=1.5

[nomoresonys]

Re: Samsung UN55HU8550F - No picture, No sound

sometimes its as simple as one bad cap, can try heat up the electrolytic caps on powerboard for a couple minutes with a hairdryer, then try it while theyre still hot, see if tv comes on or stays on longer, no joy heat the rest of the caps including the ceramic ones and try it. see if the clicking stops for a bit.

[KYBOSH]

Re: Samsung UN55HU8550F - No picture, No sound

pretty sure that the powerboard should not be clicking repeatedly with the mainboard unhooked or with mainboard and or backlights unhooked, that's what makes me think there may be a powerboard issue, did you look over all the solder joints closely, examples of bad joints: https://www.google.com/search?q=bad+...ih=607&dpr=1.5

Okay, I'll reflow the joints on everything I can get my hands on today.

sometimes its as simple as one bad cap, can try heat up the electrolytic caps on powerboard for a couple minutes with a hairdryer, then try it while theyre still hot, see if tv comes on or stays on longer, no joy heat the rest of the caps including the ceramic ones and try it.

Interesting... I'll try this after checking if the re-soldered joints doesn't work. Thank you @nomoresonys!

[KYBOSH]

Re: Samsung UN55HU8550F - No picture, No sound

pretty sure that the powerboard should not be clicking repeatedly with the mainboard unhooked or with mainboard and or backlights unhooked, that's what makes me think there may be a powerboard issue, did you look over all the solder joints closely, examples of bad joints: https://www.google.com/search?q=bad+...ih=607&dpr=1.5

I went over the SMPS this morning looking for any cold solder joints but I really didnt see anything. I reflowed all the joints with my soldering iron (on the hot side) anyway. Attached are some pics of how the joints of the caps, bridge rectifier and transformers looked before I touched them up.

The boot loop problem still persists.


I then tried heating the caps (mostly the big ones on the hot side - right hand side in the photo) but that had no real effect unfortunately. I completely agree that the clicking relay is a strange symptom. Even with the power cord unplugged, the relay will click once or twice before finally falling silent. But this TV is too new and Samsung's quality and quality control is too good to have cold solder joints only after 8 years. That and these boards arent subjected to nearly as much stress as their plasma predecessors. But it is extremely curious nonetheless. There is only 1 relay and its right next to the mains so Im not sure what its clicking could indicate.....

I may pull all the caps out of circuit and test them for capacitance and ESR just to eliminate them, once and for all, as a suspect.

[KYBOSH]

Re: Samsung UN55HU8550F - No picture, No sound

After touching up the power supply I focused my attention on the possibility that this maybe an EEPROM/Firmware issue.

I found 2 chips which could be the EEPROM which the firmware resides.
W25Q128FVIG located at IC10 (pictured in post #30) and W25Q16DVS located at IC800. Both are very close to the processor and both are marked with a highlighted marker by the manufacturer so they are obviously very important but I dont have enough experience to know which is which.

Either way i read both chips with the programmer and ask the firmware gurus for guidance.

The mainboard part number is: BN94-07389U
The panel's part number is: CY-KH055FSLV1H

Both BIN files are posted here as well.

Anyone have any idea what's what?

[nomoresonys]

Re: Samsung UN55HU8550F - No picture, No sound

well samsung is not the company it use to be, the quality and quality control is pretty much nonexistent anymore, slap them together with the cheapest substandard parts and components and sell to the people that still think samsung stands for quality, the recapping sounds like a good idea, the hairdryer will only revive a marginal cap for a bit if they are too far gone it won't help to determine a bad one.

[nomoresonys]

Re: Samsung UN55HU8550F - No picture, No sound

you should see all the bad reviews and complaints about samsung major appliances, like their fridges and washer and dryers etc, etc.

[Storyteller12]

Re: Samsung UN55HU8550F - No picture, No sound

I don’t think the eeprom is your issue. That wouldn’t cause the power supply to click. Most eeprom issues seem to be on the ku, mu series it seems like.


I just fixed a 65” version of this tv. Didn’t have a click sound like yours but was boot looping. Turned out to the buffer board tape that grounds the board to the frame of the tv. They placed the tape over he grounding pad and on top of a ceramic cap.

It was shorting out. Looked like it came from the factory that way. Not sure how it worked as long as it did.

However it’s fixed now.

[Storyteller12]

Re: Samsung UN55HU8550F - No picture, No sound

Have you tried unplugging the lvds cables going to the panel from the tcon and turning the tv on? This is just to test and see if the tv reboots or stays on.

Just want to rule out a failed panel.

[KYBOSH]

Re: Samsung UN55HU8550F - No picture, No sound

Well the great @lotas says the a reboot/boot loop is indicative of a problem with the eMMC.
Im doing some research on the issue. I dont immediately see where to get another eMMC or have this one reflashed BUT I do have this spare board that came with the TV.

What would be the chances of it having a good eMMC?
I'd love to swap it out and find out!

edit to add:

It seems the EEPROM issues can cause cyclic reboots as well.
I need to eliminate as many potential causes as I can.