Samsung UN65js8500F, no sound, blank screen and T-Con board with one LED on

[mrtek]

Hi I am new to this kind of repairs but I want to learn..I have a Samsung UN65JS8500F. the TV used to work and I tried to fix darker areas in the middle only ( img 1,2,3). I thought the led strip were bad..not the case. I did not research in advance what kind and where the LED were located. In this model they are located vertically on right and left side. Took the TV apart and put it back together. Now the tv shows no welcome screen and no sound is available thru the speakers. ..just a black screen..Backlight LED do turn on...also noticed a 5 blink code , not sure if that was there before. I can turn TV on and off with remote..Also the T-CON board only shows one out of 2 blue LED lit, the second one only blinks very fast for a short time with panel connected...from my research both led should be lit, with no panel load or am I incorrect? 12V and 3.3V are available on T-CON board but no other major voltage like 32 V. PWM voltages from PS are on. Any thought of what I should check? Already have a new T-CON and Main board , suggested on other forums but did not fixed issue.

Any help is appreciated.

Thank you in advance for your time.

[EazyBone]

My guess is you broke something on the panel.. if everything was working fine b4 tear down.

Try and disconnect one ribbon at a time, the I shaped yellowish ribbon on the buffer boards.. and then plug it in and see if 3/4 a picture shows up on either side of screen. Only do it with TV unplugged and make sure you unplug the side closest to middle so you don't short anything. Let us know if anything happens.


Also did you reapply grounding tape when you put it back together?

[mrtek]

Hi EazyBone
Thank you for your reply. Assuming that the panel is damaged, and everything else stayed the same , with the 2 T-con cables going to the panel, shouldn't the T-Con board LEDs be turned on, no load on the T-Con? I tried your test and the result is the same. Actually the 2nd T-Con led , this time it did not blink.

The grounding tape was reapplied and checked continuity between the buffer boards and chassis.

[EazyBone]

This is just a guess.. the panel. All you did was tear down the TV not fix the lights because you said they were working and then put it back together correct?

I only say the panel because it's delicate and people tend to have accidents with it pretty easily.

THese one connect box tvs get tricky. Can we get a pic of each board close up

[mrtek]

EazyBone

I wanted to let you know that I have purchased suction cups specifically for this kind of work. See attached images.Let me know if need more images.

Thank you

[lotas]

You forgot to install the cable, T-con did not see the panel, since the feedback from the panel was broken and the output voltages were blocked and the LEDs did not light up on the t-con.

[EazyBone]

I don't think I would have an idea of what to do next .. maybe lotas would. But definitely this cable isn't seated correctly on your main board. If that could of messed something up I'm not sure.

[mrtek]

Lotas

thank you for the reply. The cable was disconnected to test EazyBone solution. I have seen a couple of video where the 2 panel cables were disconnected from T-Con and the leds turned ON. Is every Samsung LED TV looking for a feedback from the panel? With the panel cables connected and power off I have checked for shorts on the buffer boards to GND. Could not find any. Any places I should check?

Thank you

[mrtek]

EazyBone

I will reset the cable.

[lotas]

Lotas

thank you for the reply. The cable was disconnected to test EazyBone solution. I have seen a couple of video where the 2 panel cables were disconnected from T-Con and the leds turned ON. Is every Samsung LED TV looking for a feedback from the panel? With the panel cables connected and power off I have checked for shorts on the buffer boards to GND. Could not find any. Any places I should check?

Thank you

All modern Samsung TVs have feedback (T-con panel), so you saw that two cables were disconnected and the LEDs were on, which means a feedback jumper was installed on the t-con (simulating that the panel is connected), this is for diagnostics.

[mrtek]

Lotas

it makes sense. I saw this video and thought that would work as well.
https://www.youtube.com/watch?v=9v4T...JlZW4gcmVwYWly.

[lotas]

From a short circuit in the panel or on the buffer strips, T-con will also block the supply voltage for the panel, check carefully all the cables on the back side where their contacts are located, they are very delicate and fragile and if installed incorrectly in the connector they can break, move and short-circuit with each other...

[lotas]

It’s hard to see here, the metal support does not close the components...

[mrtek]

OK. Lotas

I will check on that. Thank you

[mrtek]

Hi Lotas

what you saw in the image is bare copper text. No components there.

[mrtek]

An update. It seems that I found a short on the panel boards and it seems that it runs across the panel , left and right. It is a dead short between the 2 points marked in the images. Not sure what differential signals they are. it seems that they have a pulldown resistor on the line. Not sure what else it can be done. it does not look like a power line. Maybe I am wrong.
Also, can somebody tell me what the 2 circled devices are? They are only on the left side of the panel board.

Thank you again for your input.

[mrtek]

More updates. Now that I have a sample to work on, (the Samsung UN65JS8500F TV), I would like to debug other issues. I have 2 sets of boards,Main and T-Con (Power Supply still original). they both behave the same way. The StandBy LED flashes 5 times indicating some sort of issue. Is this issue related to the main board or because is it read on the power supply board?
I have unplugged the T-Con from the Main board. Also the Blue-Tooth and WiFi modules are disconnected. Only main board and PS are connected. They both behave the same way. The StandBy LED flashes 5 times indicating some sort of issue. Is this issue related to the main board or because is it read on the power supply board?When power is applied, the backlight LEDs are coming on, the StandBy LED flashes five times and then it shuts off.
Looking at the repair manual, CN201 connector table, from main to power supply, on pin 11, signal called SMPS_FET_Fail_Detect, is HI or at 3.3V either in standBy mode or with TV on. Is this signal normally LOW or at ~0V to indicate proper functionality to the main board and therefor turn on all the power supply / voltages on the T-Con board? Is this called main board full protection and that is why there is no sound /startup chime? If the sound output was selected to be another source besides the TV speakers, will the main board remember the selection regarding if the TV is plugged in or not ( StandBy mode) or will it default to the TV speakers if everything is OK?

Thank you