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

[KYBOSH]

why you are jumping between youtube... u will never have answer there,,, just answer lotas last question.. if they are fine then u need to take out the bezel and carefully with loop check the round display glass

Here is a screenshot of the YT video i linked above. At the 20 second mark he demonstrates how the display is powered but with no image.



I have seen this phenom before (in other TVs) but didnt realize what i was looking at.
At its face its an amazingly simple method to see what is going on I think.
I would have never thought to try it (and actually didnt) until i saw this demonstration on YT.

Invaluable resource for lowly people like me!


Edit to add:
Oh No! I see you have history with these types of videos!
I will read more and try to get a handle of the situation.

[Davi.p]

My suspicion is that in this strange design of Sony half of the tcon function is on the main board and half is on the separated board, this is by observing the high number of pins on the two MB output connectors exceeding the lvds lines, and the fact that twins lvds lines runs to those connectors, besides this also the strange fact that the "extra tcon" runned alone did not produce self test, this is why i'm thinking you have bad main board, maybe a bad solder under big Mstar chip, or bad related flash chips.
If you want to investigate more you can try to hook a pc to the optional uart port on CN4201 and see the log for errors, you can post it here attached.. which eorom programmers have you?

PS: the finger tapping on the black screen revesls only a working back light, but the lcd can be or cannot be working/fed..

[KYBOSH]

My suspicion is that in this strange design of Sony half of the tcon function is on the main board and half is on the separated board, this is by observing the high number of pins on the two MB output connectors exceeding the lvds lines, and the fact that twins lvds lines runs to those connectors, besides this also the strange fact that the "extra tcon" runned alone did not produce self test, this is why i'm thinking you have bad main board, maybe a bad solder under big Mstar chip, or bad related flash chips.
If you want to investigate more you can try to hook a pc to the optional uart port on CN4201 and see the log for errors, you can post it here attached.. which eorom programmers have you?

PS: the finger tapping on the black screen revesls only a working back light, but the lcd can be or cannot be working/fed..

First off, thank you very much for explaining the screen tapping phenomenon. I usually don't feel like I have egg on my face but this YouTuber got me!

If the mainboard is the problem then I would have egg on my face again!. It gives sound get sound, response to input,ect, accepts firmware updates... everything that would indicate that its a good mainboard. Plus the troubleshooting flowchart (I posted above) for this model does not list the mainboard as even a probability at all.

But we have eliminated just about everything along the way so unless there is something obvious anyone can point out about the behavior of the panel i have no problem switching gears to look at the mainboard.

I have a lowly CH34A1A Multiprogrammer and a few basic accessories that came along with it. I will have a look a CN4201 to see what I need to communicate with it.

[Davi.p]

You posted a chart in the first posts, under the voice No video on all inputs , the main culprit is B board that is main.board.... the software doesn't apply, i say the suspect is the Mstar chip that is part of video output, not main processor!

cn4201= pins from.the left= 1- 5v power (ignore it), 2- gnd, 3/4- TX/RX.. to find what between tx rx check voltage in them, the one with a voltage is TX, i hope... use your ch341a with setting for serial port (jumper), then search an old desktop pc cd rom drive audio cable 4 pin, and use it on to the ch pins, the other end cut connector and solder to board.. in pc get a terminal program like the ancient Hyperterminal or another..

[lotas]

Sony often has problems with LVDS cables themselves (poor quality), try replacing them.

[KYBOSH]

Sony often has problems with LVDS cables themselves (poor quality), try replacing them.

Thank you Lotas. I replaced them earlier this week with brand new ones direct from Sony distributor (encompass.net).
Davi.p suggests that I am dealing with a mainboard issue.

I did some searching and found Nick's Electronics Repair (not to be confused with Nick's TV Repair!) offers repair service for this mainboard but the price is pretty hefty ($150US).
One of the symptoms listed is "White standby light, but no picture." That sounds like this situation right here.

Replacement boards on ebay are more expensive.

Before I got down that route I'd like to try what Davi.p is suggesting about reading the error codes.
I have never done this before so this is just the type of novel experience Im was hoping to learn.

[lotas]

Have you replaced these?

[KYBOSH]

Have you replaced these?

Yes Sir I replaced both with brand new ones.

[nomoresonys]

Any update on those t-con voltages?

[KYBOSH]

Any update on those t-con voltages?

Sorry nomoresonys
Im currently looking for those test points.
Its not easy finding them... very tiny markings.

[lotas]

You should have voltages across each inductor relative to ground...

[KYBOSH]

You should have voltages across each inductor relative to ground...

THANK YOU FOR THIS

This actually reminds me of the weird magnetic field - LED trick i discovered on Youtube and posted about.

I checked for voltages across all the inductors you marked and NONE HAD VOLTAGES except L2 (large gray one) and it was only reading 1V.

[lotas]

It is clear that there will be no voltage anywhere, since you do not have 12v to power the T-CON.

Is there 12V at the fuse output, relative to ground?

[KYBOSH]

It is clear that there will be no voltage anywhere, since you do not have 12v to power the T-CON.

Is there 12V at the fuse output, relative to ground?

Yes i have 12v+ on the fuse. It was my sanity check when i wasnt seeing anything on the inductors. This is the new TCon also. Amd the 2 processor chips there are hot.

[lotas]

If there is no voltage on the inductors, then most likely it went into protection, carefully install a thin wire! jumper feedback with the panel and disconnect the cables from the panel one by one and see if voltage appears on the inductors...

[KYBOSH]

If there is no voltage on the inductors, then most likely it went into protection, carefully install a thin wire! jumper feedback with the panel and disconnect the cables from the panel one by one and see if voltage appears on the inductors...

Just to be clear:
Step 1: with the power OFF, solder a thin wire between the two test points you illustrated in the picture.
Step 2: With the power ON, test for voltage at all the inductors with I) both FFC connected II) either L or R FFC connected and finally III) no FCC connected.

Is this how you want this experiment done?

[lotas]

And another question, how did you measure the voltage on the inductors (options 1 and 2)? If the processors are heating up, it means they are receiving voltage, but not as 12v, which means there should be at least some low voltage on the inductors 1.2v, 1.8v, 2.5v, 3.3v...

[KYBOSH]

And another question, how did you measure the voltage on the inductors (options 1 and 2)? If the processors are heating up, it means they are receiving voltage, but not as 12v, which means there should be at least some low voltage on the inductors 1.2v, 1.8v, 2.5v, 3.3v...

I mentioned that L2 (the large gray inductor) is measuring 1V.
I measured it against the ground of the screw securing the TCon to the chasis,

[lotas]

Just to be clear:
Step 1: with the power OFF, solder a thin wire between the two test points you illustrated in the picture.
Step 2: With the power ON, test for voltage at all the inductors with I) both FFC connected II) either L or R FFC connected and finally III) no FCC connected.

Is this how you want this experiment done?

With the TV turned off, install a jumper and disconnect one cable, turn on the TV and check the voltage, then turn off the TV, connect the cable that was disconnected and disconnect the second cable and also check the power supply on the inductors...

You can first disconnect both cables, voltage should appear on the inductors...

[KYBOSH]

With the TV turned off, install a jumper and disconnect one cable, turn on the TV and check the voltage, then turn off the TV, connect the cable that was disconnected and disconnect the second cable and also check the power supply on the inductors...

You can first disconnect both cables, voltage should appear on the inductors...

Thank you for the clarification!
I jumpered both testpoints together and removed bother FFCs.
The voltages are exactly the same.
0V everywhere except L2 which has 1.1V.

I didnt bother testing with only 1 cable on given that result.
If you think i should please let me know.