Trying to Save - SONY BRAVIA KD-75X780F - No Picture BUT there’s sound

[KYBOSH]

Previous owner said TV just went blank one day.
They attempted to open the back panel and yanked the power connector off the power supply in the meantime.
Easily fixed that and got the TV to turn on. Backlights come one with everything connected. Good Sign.
The mainboard shows signs of life (red light on digital audio out is on) but that's about it. Good Sign.
There is not blinking LED and the most importantly there is LED response and sound when I press the MENU button on remote control. GREAT Sign.

I just downloaded the Sony KD-75X7800F Service Manual and am going through it now but wanted to see if anyone might have a quick and fast test I can do to narrow down the issue.
The manual says it's most likely the “B board”. Im not sure which board that is…

Thank you in advance

[KYBOSH]

Hello everyone. Hope you are all well and in good spirits.
I wanted to update this thread with information that I have found since I last posted.

I found a good guy on ebay who agreed to test the mainboard for me for a bench fee.
He told me initially that these TVs are known for their panels dying but I wanted to be absolutely sure it was the panel and not anything else since we have been working on this thing for several months.
So he agreed to test it for me by putting it in another (similar but not same) TV model. Still dont know what model TV he used as I thought these mainboards were quite specific to the models they were made for.

Anyway the mainboard is fine and he was good enough to send pics as proof of life.
So Im at the end of my journey with this set.
I may never be good enough to do short detection and remediation on these LCD panels.
And even if I eventually could I certainly cant do anything like that now.

Thank you all for your help, input and expertise. I learned a lot and enjoyed the experience.
Hope this helps the next journeyman who has the same or similar symptoms.

[Diah]

its android... if you have 12V VCC on T-con Fuse from both side,,,, try disconnect the U ribbon cable at the middle if each side on the panel buffer boards to see if there will be 3/4 picture

[KYBOSH]

its android... if you have 12V VCC on T-con Fuse from both side,,,, try disconnect the U ribbon cable at the middle if each side on the panel buffer boards to see if there will be 3/4 picture

I didnt follow/understand these instructions very well.
would you mind pointing out which cable i should disconnect??

thank u!

[Diah]

not these 2... this is ribbon cable.... take out the 2 speaker... and if there metal plate cover the panel buffer boards remove them too... at the middle you will have flat cable like the letter U connect 2 parts of boards together you need to remove from each side a time... of course after you check the T-CON fuse F1 had 12V at both side with reference to TV chassis

[KYBOSH]

not these 2... this is ribbon cable.... take out the 2 speaker... and if there metal plate cover the panel buffer boards remove them too... at the middle you will have flat cable like the letter U connect 2 parts of boards together you need to remove from each side a time... of course after you check the T-CON fuse F1 had 12V at both side with reference to TV chassis

Thank you! I actually figured out what you were referring to. The word "U cable" jumped out at me when i read it a 4th time and i instantly knew what you were refering to. I will have to do a bit more disassembly tonight when i get back home. I can also confirm i am getting 12.7v on both sides of the fuse.

[KYBOSH]

not these 2... this is ribbon cable.... take out the 2 speaker... and if there metal plate cover the panel buffer boards remove them too... at the middle you will have flat cable like the letter U connect 2 parts of boards together you need to remove from each side a time... of course after you check the T-CON fuse F1 had 12V at both side with reference to TV chassis

Okay I got the plate covers off and removing one U cable at a time to see if I got a picture or any signs of display life but I got NONE.
I removed one, then the other, then both but NO JOY.






I then reconnected them pulled out my FLIR to see if there was a short on the buffer boards but they were cool as a fan.
I scanned the T-Con itself and the two processors appeared to be operational (showed normal heat).

I cannot find anything out of the ordinary.

[Diah]

I cannot find anything out of the ordinary.

okay , from the T-CON photo you posted, it work on separated 2 channel,, so you can disconnected one ribbon cable a time between T-CON and Panel. if no result.
mean need to have another ways to test.
1- before all need to do hard reset ... plug the tv out from wall.. push the joystick and pull it down. keep it in this positionthen plug the Tv in wall... release your pushing only after the front LED change from White to green... donnt touch any things leave it it could reboot 2-3 time... at time it have The first install you will hear melody... keep it 10-15 minute at this melody so we will be sure it booted and installed android complete.
if no avail after hard reset.

2- t-con panel in stand alone ( to see if you got sign on screen ) if yes mean the MB cutting Video signal ), No mean the T-CON cutting the signal

[KYBOSH]

2- t-con panel in stand alone ( to see if you got sign on screen ) if yes mean the MB cutting Video signal ), No mean the T-CON cutting the signal

Thank you for this. I will get started on it today. Can you describe the procedure in detail on how to get the t-con and MB in stand alone mode?

[Diah]

Thank you for this. I will get started on it today. Can you describe the procedure in detail on how to get the t-con and MB in stand alone mode?

stand alone are not with MB, the MB first need to hard reset if nothing change then we do stand alone between PSU + T-CON + Panel ONLY.... the MB we should disconnected from the whole boards.

i need photos of the whole back of the TV to show how boards connected together... and photo of the PSU socket which iz goes to MB.. you will find also Print chart of the sockets show the PINs NO and its name.

[KYBOSH]

stand alone are not with MB, the MB first need to hard reset if nothing change then we do stand alone between PSU + T-CON + Panel ONLY.... the MB we should disconnected from the whole boards.

i need photos of the whole back of the TV to show how boards connected together... and photo of the PSU socket which iz goes to MB.. you will find also Print chart of the sockets show the PINs NO and its name.

I disconnected the FCC for the right right side buffer panels at the T-Con - no video.
I reattached it and the tried the left side - no video.
i reattached it then disconnected the left, right, then both flex cables coming from the MB - no video.

I am now looking into doing the hard reset.
My TV has 3 buttons and not a single one but I found the instructions on the SONY website


Perform a Force Factory Reset on Android TV™ or Google TV™ (if the TV has one or three buttons)


Edit to add: i have completed the reset and the TV is currently at the setup Welcome screen (i can hear the melody playing) but there is still no video.

[Diah]

i reattached it then disconnected the left, right, then both flex cables coming from the MB - no video.

so when you disconnect both the 2 LVDS cable which coming from MB to T-CON :
1- did you have the LED BL come on?
2- did you have 12V on T-con fuse from both side ?

[KYBOSH]

so when you disconnect both the 2 LVDS cable which coming from MB to T-CON :
1- did you have the LED BL come on?
2- did you have 12V on T-con fuse from both side ?

I did indeed have LED BL on with both LVDSs disconnected.
I did not check for voltages across the fuses but i just redid this step and i do have 12.7v on both sides of the fuse (checked against the chasis).

[Diah]

I did indeed have LED BL on with both LVDSs disconnected.
I did not check for voltages across the fuses but i just redid this step and i do have 12.7v on both sides of the fuse (checked against the chasis).

and you hear the melody ?
and the front LED white ?
its some things strange,,, no error or the front led show different color !!
then no need to do any stand alone test... because this what you did are like stand alone test just t-con and panel... and yours T-CON didn't start

let do deep investigation on yours T-CON.. first put back the 2 LVDS
1- check first the 2 NOR Flash Winbond at Pin 8 what voltage you have
2- testing any SMD 0R

[KYBOSH]

and you hear the melody ?
and the front LED white ?
its some things strange,,, no error or the front led show different color !!
then no need to do any stand alone test... because this what you did are like stand alone test just t-con and panel... and yours T-CON didn't start

let do deep investigation on yours T-CON.. first put back the 2 LVDS
1- check first the 2 NOR Flash Winbond at Pin 8 what voltage you have
2- testing any SMD 0R

Correct. With both LVDS cables disconnected i have melody, i have backlight and my status LED is solid white. This set has never given me a single error code not has it shutdown or restarted inexplicably.

I will do the testing you described tonight when i get back home.
thank you for the assist!

[KYBOSH]

let do deep investigation on yours T-CON.. first put back the 2 LVDS
1- check first the 2 NOR Flash Winbond at Pin 8 what voltage you have
2- testing any SMD 0R

Sorry for the delay.
I tested the 7 0R I found on the board (RH1 through RH6 and RM21) and they all had continuity (0.2Ω).
I then checked PIN 8 on the two Winbond 25Q16JV NOR Flash memory chips at IFF1 and IFF2 and both read 3.3V against the ground of the chasis.

[KYBOSH]

Diah et al. Any tips on my next step?

[lotas]

Diah et al. Any tips on my next step?

Well, the next steps, you have many control points on the t-con with the indicated voltages, so you need to check them, find more points VGH, VGL,... and check if there are voltages on them. This Samsung t-con and disconnecting the light or right cable will not work here, you need to connect it (put a feedback jumper FB_ Panel - T-con).

[KYBOSH]

Well, the next steps, you have many control points on the t-con with the indicated voltages, so you need to check them, find more points VGH, VGL,... and check if there are voltages on them. This Samsung t-con and disconnecting the light or right cable will not work here, you need to connect it (put a feedback jumper FB_ Panel - T-con).

Thank you for the assist here! This is my first time working on a T-Con on a component level so please be patient with me. Could you point out the test points (from the picture) that i need to check? And where is this feedback jumper you mentioned at the end?

[Davi.p]

When you do the screen self test, you have to keep the main board attached tothe PSB so you can watch if the power led blinks, and you have to wait some seconds, the first color to appear in the color sequence is the black, then white..

[lotas]

Well, these points, there are a lot of them, you need to carefully examine them...