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

[KYBOSH]

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..

Diah mentioned that no self test was needed as we sort of established that the T-CON does not start up at all even when both LVDS cables disconnected. When i diconnected the LVDS cables the Mainboard was still connected to everything else (including the power supply board) and the TV still acted like nothing was wrong (no error blinks, LED came on, and I got melody from the Android setup screen). Only thing missing was display. Or acknowledgement that there was something wrong somhwhere (LED error blinks or failure to start at all).

[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).

I just want to verify that you meant SONY T-Con and not Samsung as you wrote above.

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

Okay I will connect everything and test these points while the TV is running.
I should be able to remote back on the 6 spots you pointed out above.
Thank you!

[KYBOSH]

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

Tested and confirmed that some test points are reading 0V while others are reading just fine.

AVDD1 = 0.0V
AVDD2 = 0.0V
AVDD1.8 = 1.8V
BVDD1.8 = 1.8V

HVIN_12V = 0.0V
PAVDC(?) = 0.0V
VOFFE_.11 = 0.109V

Can you share what you understand from these readings?

[Davi.p]

It doesn't matter what says Diah.. at least for me.. but seeing what you wrote on last post the tcon is indeed not fully working, check also the restpoint VDD_1.05.. This tv is from Sony but screen is from Samsung..

plus.. the self test as you reported is not performed well, you detached first one input cable, then another one.. no, you have to detach both then apply current input on power board, otherwise the tcon will not initialize..

[KYBOSH]

It doesn't matter what says Diah.. at least for me.. but seeing what you wrote on last post the tcon is indeed not fully working, check also the restpoint VDD_1.05.. This tv is from Sony but screen is from Samsung..

plus.. the self test as you reported is not performed well, you detached first one input cable, then another one.. no, you have to detach both then apply current input on power board, otherwise the tcon will not initialize..

Not a problem!

As you instructed I went back and tried to do the self-test exactly as you described.
With the TV powered off I removed BOTH LVDS cables.
Then I powered the TV on with the remote.
I got proper backlight, an accompanying melody from the setup page and the LED status light was solid white (not blinking or showing anything out of the ordinary).

After powering off the TV and reconnecting both LVDS cables I tested the LDD_1.05 voltage and it read as good (1.085V against the chassis).
I noticed another testpoint below the other LVDS cable called VCC_F_3.3V (which seemed to be the sister of LDD_1.05 though maybe unrelated) so I tested it and it also showed as good (3.3.07V against the chassis).

Im looking to actually learn how to repair this T-Con rather than a simple swap out.
The replacement isnt particularly expensive but I figure i would give it a shot as I rarely come across an opportunity like this.
Eager for all of you guy's guidance!

[Davi.p]

Regarding the panel self test, you forgot to say about what displayed the panel, do mention of it , i'm not sure what you know what not, the screen must show black,white, green, red, blue.. first black.. cycling..

[KYBOSH]

Regarding the panel self test, you forgot to say about what displayed the panel, do mention of it , i'm not sure what you know what not, the screen must show black,white, green, red, blue.. first black.. cycling..

So sorry! The display is black. Always black. Never changes. No signs of life or video. Not even a flash or flicker.
Also on the buffer boards of the display no SMDs get warm at all (inspected with FLIR camera). Also there is no change when I remove either U-cables (which connects the buffer boards on either the left or right side).
I have not established if the panel itself is good but we have pretty much established that the T-Con doesnt seem to be activating nor is it throughing an error code as the mainboard seems oblivious to what the T-Con is or isnt doing.

[KYBOSH]

Bump for Davi.p's input and further instructions.
Thanks in advance!

[Davi.p]

Sorry.. hard work days these days.. i hope i can help the same.. i'm suspecting the two spi flash on the tcon, it's solder, it's data, or both.. i notice on the main board there are two processors, the main one and the video preprocessor, i don't know if the preprocessor has a built in or connected software that handles tcon communication, in that case a preprocessor bad balls could produce all the present defect, my bet is on the second scenario.. bye..

[KYBOSH]

Sorry.. hard work days these days.. i hope i can help the same.. i'm suspecting the two spi flash on the tcon, it's solder, it's data, or both.. i notice on the main board there are two processors, the main one and the video preprocessor, i don't know if the processor has a built in or connected software that handles tcon communication, in that case a preprocessor bad balls could produce all the present defect, my bet is on the second scenario.. bye..

Thank you my friend for taking that time here.
If you comeback and can answer this question that would be great... its also an open question for anyone else who might care to offer an opinion: If the issue might be related to a failed processor chip then why do we not get anything when we do the T-Con self test? Meaning to say the mainboard is completely disconnected so any issues with it would not stop the T-CON from sending a test pattern to the display.

The way I see it now is I might have to just start throwing parts at it to see what's what. Which would be a shame as I would like to think myself a better detective that than!

[Davi.p]

yes your reasoning is right.. so are you able to try to fix the spi flash? Or you willing to try to find a replacement tcon? Always better to ask for one coming from working tv cracked panel..

[KYBOSH]

yes your reasoning is right.. so are you able to try to fix the spi flash? Or you willing to try to find a replacement tcon? Always better to ask for one coming from working tv cracked panel..

Thank you for the reply! Yes I have do have some experience with repairing SPI flash issues although this did not strike me as an EEPROM (from my limited experience).
Which chip should I read the dump from?

[Davi.p]

there are 2 clearly visible SPI flash ic on the tcon, if you don't search the dump online (i think them are twins) it's not much of help reading them..
8pin ic marking 25qxxxx usually

[lotas]

KYBOSH you can take a high-quality close-up photo of this area.

[KYBOSH]

KYBOSH you can take a high-quality close-up photo of this area.

As requested Sir!

[lotas]

Check the resistance between these points (FB) feedback, 1 - with the cables connected to the panel, 2 - with one cable disconnected, 3 - with the second cable disconnected, 4 - with two cables disconnected.

[KYBOSH]

Pardon me but I am not really familiar with how to take these readings as you described so if the measurements I present to you dont make any sense ....

	Both FCCs On	Right FCC Off Only	Left FCC Off Only	Both FCCs Off
FB_VRB + FB 332	2MΩ↑	51.3KΩ	4.18KΩ	2.4MΩ
FB_1 + FB 331	6.13KΩ	11.81KΩ	2.58KΩ	3.1MΩ

FB_VRB and FB 332 are on the right side of the T-Con board while the other two are on the left.
I dont know what to make of these numbers but one thing stood out.
When both cables were connected the resistance between the points FB_VRB and FB 332 was very high and increasing quickly (denoted with a red arrow).

If I took these readings wrong please let me know and how it should be properly done so I can go back and sort it out.
I could not find anything online describing how these feedback points were supposed to be tested.

[lotas]

FB 332 + FB 331 ?, FB_VRB + FB_1 ?

[Davi.p]

The inner connector test points are tied together on the tcon board so you have to always measure 0ohm from 1 to the other.. when both FFC are connected you have to read 0ohm every measure combination.. so i guess you have faulty FFC ribbons or faulty multimeter cables.. if you have FFC in to the side of FB_1 then FB_1--> FB331 must check 0hm.. similar the other connector..

PS: check very often multimeter crossed probes in ohm, a good DMM and good cables must check around 0,1-0,0 ohms, post a picture of you meter, if you didn't already..

[KYBOSH]

FB 332 + FB 331 ?, FB_VRB + FB_1 ?

	Both FCCs On	Right FCC Off Only	Left FCC Off Only	Both FCCs Off
FB_VRB + FB_332	2MΩ↑	51.3KΩ	4.18KΩ	2.4MΩ
FB_1 + FB_331	6.13KΩ	11.81KΩ	2.58KΩ	3.1MΩ
FB_331 + FB_332	14.4Ω	5.6kΩ	5.6kΩ	9.5kΩ
FB_1 + FB-VRB	2MΩ↑	2MΩ↑	2MΩ↑	13MΩ↑

Note: This is with the TV off, disconnected from the mains and both LVDS cables connected (if this makes a difference).