Sony KD49X8000H - Sound, backlight, no picture

[MoreMagnets]

Hello all!

This post will mostly just act as documentation for my undertaken troubleshooting steps for this TV. Advice will also be appreciated for things to try next

Picked up the TV in thread title from a retail returns auction, symptoms were as described. I started my troubleshooting attempts by shorting the 19V PSU rail to the 3v rail with my multimeter... Doh. Big spark, dead PSU, TV not turning on anymore. Picked up a new mainboard and PSU locally from someone here in Sydney, wasn't sure if my butterfingers had killed both and was a big drive to pick them up. TV is now booting again with same symptoms.

As I was getting sound and response from the remote when scrolling menu's with the remote I skipped straight to the TCON board and below. Tried disconnecting one side of the gate driver ribbons at a time.

(left and right as looking at back of TV)
Left cable removed, right cable installed:
Full black screen, sound, backlight
Right cable removed, left cable installed:
Right side of screen is white, left half black, sound, no image.

At this point I was thinking it was a TCON board AND a bad panel, measured TCON voltages with right side cable removed:
Vin: 12.65v
VGH: 28.98v
HVDD: 9.18v
VGL1: -6.92v
VDD: 16.65v
Vcore: 1.096v
VCC_33: 3.296v
RS1: 1.61v

Most points measured as 0v or close to 0v when the right side ribbon was installed, so short present somewhere on the gate driver board or beyond that was sending TCON into safety. Tested continuity on caps on gate driver board, no full shorts.

At this point I was a bit lost, searched the far corners of the internet and found the friendly folks here at BadCaps. Saw a bunch of suggestions to try the "tape trick" and thought why not, what have I got to lose.

I got image back!

initially started with a large piece of tape over first half of the 8 clock pins (pin 2-5), isolated pin 4 CLK3 to be the troubled pin that was killing the TCON output.

Where I am at currently:

Blocking pin 4 only lets the TV display an image. But it is pretty heavily plagued by horizontal lines, so I suspect there may be more than one faulty circuit in the gate driver board or panel itself. Blocking all 8 CLK pins gives me the best image as I have tested so far (but still not great), this is more likely me having trouble with the miniscule pieces of tape rather than the whole right side gate driver board being bad (I hope).

There is also a noticeable bright strip roughly 1/3 up the screen when displaying white or near white colors, this seems to show when blocking any number on pins with the tape, but does not appear when testing the half white, half black 1 ribbon TCON behavior with pin 4 blocked.

Any suggestions for next steps to try will be appreciated, will be posting my troubleshooting adventures regardless

[MoreMagnets]

Re: Sony KD49X8000H - Sound, backlight, no picture

Uploading my random voltage testing photo.

(Note photo has both ribbons connected. Tests were actually taken with the right one removed)

[MoreMagnets]

Re: Sony KD49X8000H - Sound, backlight, no picture

I have managed to follow the CLK traces down the Gate driver board to these resistors on the end furthest from the TCON ribbon cable. No short detected on panel side of any of them and they all seem to be testing a steady 100ohms.

The hunt continues!

[nomoresonys]

Re: Sony KD49X8000H - Sound, backlight, no picture

thats a very good image, wish all the photos posted were that clear, if you havent already go ahead and test those little mlcc ceramic caps for shorts or very low ohms.

[MoreMagnets]

Re: Sony KD49X8000H - Sound, backlight, no picture

No shorts or low ohms on the caps on this right side board.

Did further testing on the image with just pin 4 blocked and it looks like the bright band isn't actually present if just that one pin is out. Only when most or all of the pins are blocked. So, positive if I can figure out what is going on.

Still getting the black lines if I only block pin 4 though, tried blocking 1 other pin at a time in case it was two bad CLK circuits on the gate drivers horizontal to the panel; no dice. Could be three bad CLK circuits I guess? Further testing is required.

[nomoresonys]

Re: Sony KD49X8000H - Sound, backlight, no picture

do you have a picture of the rest of that board?

[MoreMagnets]

Re: Sony KD49X8000H - Sound, backlight, no picture

Unfortunately didn't grab one. Will get a picture when I am in front of the TV again.

I think I have potentially found the reason for my issues with black lines. Did some research and found the patent for LGs Gate-In-Panel circuitry:
https://patents.google.com/patent/US...oq=15%2f366923

As well as this handy youtube video for the function of TCONs and what different manufacturers call different signals:
https://youtu.be/izd7dhtmZjc?t=1058

From what I can tell these clock signals are cascaded into each other on an even and odd basis (CLK1 to CLK3, CLK3 to CLK5), meaning that by blocking only CLK3 I am turning on, but not driving the subsequent GIP circuits, resulting in the black bars.

I'm thinking I might try and block VGH_ODD on the right ribbon cable and see what happens. Just wanted to check in here to see if I was way off base with my findings first.

[MoreMagnets]

Re: Sony KD49X8000H - Sound, backlight, no picture

Attached images of the front of the right side panel driver board.

Blocking VGH_ODD did not fix.

The hunt continues....

[nomoresonys]

Re: Sony KD49X8000H - Sound, backlight, no picture

so no shorts on caps, are all those resistors on that board showing the proper ohms? rating is marked on resistor.

[MoreMagnets]

Re: Sony KD49X8000H - Sound, backlight, no picture

Managed to get a close up of the pixels to demonstrate the issue I'm having when blocking CK3. In this case I have blocked CK3, CK6, and CK7.

Is it just me or does it look like half on the pixels on those lines are actually activating and then skipping the next pixel? Potentially an issue with the data lines and not the clock signals as once thought?

[MoreMagnets]

Re: Sony KD49X8000H - Sound, backlight, no picture

Man I am at a loss with this thing. No shorts detected ANYWHERE. No bad caps that I could find, maybe my testing methodology is wrong? I have tested the resistance of the caps/resistors. I have also tested the capacitance of the caps, they all seem to match the board on the opposite side of the panel.

I know that blocking CLK3 brings picture back, but I do not know WHY and that bothers me to no end. I think I'm missing some critical changes that LG/Sony have made to the way the CLK signals function in these newer 4k HDR panels.

Any help would be much appreciated, the hunt continues...

[Davi.p]

Re: Sony KD49X8000H - Sound, backlight, no picture

it seems that clock lines are paired because on the magnifiy there are odd collumns clean and even ones damaged, so must find the only one pair that gives ok results.. one line controls odd colums one even, this is how 4k panels works maybe..

Have you tested the original psu? i think is ok..

PS: i'm not convinced on this because on closeup i see all 3lines are on same columns.. let me think on..

[MoreMagnets]

Re: Sony KD49X8000H - Sound, backlight, no picture

Further testing has discovered that the panel will display an image with CLK3 OR CLK7 blocked. Image is not clean with CLK3 AND CLK7 blocked.

So something that is shared between these CLK signals must be shorted.

edit: have tested the original PSU. TV doesn't respond to any input with it installed.

[MoreMagnets]

Re: Sony KD49X8000H - Sound, backlight, no picture

I believe I have found a patent that explains why blocking either of CLK3 or CLK7 will allow the display to show an image.. It looks like the signals may feed into each others node controllers, so blocking either of them essentially blocks both of them. I don't believe there is a way to only block the one that is actually having an issue.

https://patents.google.com/patent/US8860650B2

[Davi.p]

Re: Sony KD49X8000H - Sound, backlight, no picture

The true question is WHY odd columns are clean and even ones not, i think that even clocks are for the clean columns, when you block one of them them are activated by the same line on the opposite side, but odd clocks are for the damaged half of the columns, it seems that on a certain line or some, the gate output GLx is shorted to CLK or GND and remains lit (black pixels) the signal is spread to all the sets of lines connected to it, in this case the only solution hope is the method i have thought last year that is, after in some way locating the true damaged line, for example disconnecting one half of screen at a time and watching lines intensity, and drilling the screen in the right line right point to isolate that faulty driver, it's almost very hard to do that, i have made some experiments on a cracked panel.. bye