TCL 55p1us turns ON with sound and black screen

[deep000]

Hi all,

I am a newbie, i am taking this opportunity (the breakdown of my TV) to learn electronics.

I was watching the tv, and the colors became weired, i turned off/on the screen => black screen as result (sound/backlight working).

TV: TCL 55p1us
T-CON: st5461d04-1-c-7

I did some voltage tests, here is the result:

1 - VIN 12   12V 
2 - VGH     between -150 mv and -0.47V (negative ??)
3 - VGL     between -150mv and -0.47V (same value as VGH ??)
There is a continuity between VGH and VGL, is it normal ??
4 - HVAA     2.4mV 
5 - VDD 33    3.3V
6 - VDD 1V8   1.8V
8 - EN_1V8    1.65V
7 - VDD IO 33  3.29V

When i remove the ruban A only (right one), half of the screen is working (i can see a part of the TCL logo) but when i remove the ruban B only, all the screen is black.

What can i do/test to track down the problem, and found the guilty component

Thank you for your help

[lotas]

Re: TCL 55p1us turns ON with sound and black screen

You have a bar "A" on the matrix (panel) greatly underestimates the power supply VGH and VGL (short circuit on these lines), the blocking ceramic capacitors on these bars usually short, you need to ring these capacitors with a tester

[lotas]

Re: TCL 55p1us turns ON with sound and black screen

These are roughly what you need to call the tester

[RDC55]

Re: TCL 55p1us turns ON with sound and black screen

And if you don't find any shorted MLCC's then you might get it going by adding tape to the ribbon cable to isolate the bad component.

[deep000]

Re: TCL 55p1us turns ON with sound and black screen

Thank you for your replies !

You have a bar "A" on the matrix (panel) greatly underestimates the power supply VGH and VGL (short circuit on these lines), the blocking ceramic capacitors on these bars usually short, you need to ring these capacitors with a tester

How did you know that the problem comes from the panel and not the t-con ?

These are roughly what you need to call the tester

I will try to test them, i read that i must unsoldered them to do it (Flux + heat).
What worries me is how to resolder, i have 0 idea how to solder such tiny component.

And if you don't find any shorted MLCC's then you might get it going by adding tape to the ribbon cable to isolate the bad component.

Can you explain more.

[RDC55]

Re: TCL 55p1us turns ON with sound and black screen

Thank you for your replies !I will try to test them, i read that i must unsoldered them to do it (Flux + heat).
What worries me is how to resolder, i have 0 idea how to solder such tiny component. Can you explain more.

You do not need to even think about desoldering until you have proven there is a short on that side, which can easily be done by checking across the capacitors with a DMM. Most of the caps are in parallel, so if you do find a short then report back to get some help on finding the defective one.

For doing the tape this video covers it quite well and it just happens to be a TCL 55 inch.

https://www.youtube.com/watch?v=pfrRhw7-ZII

[deep000]

Re: TCL 55p1us turns ON with sound and black screen

You do not need to even think about desoldering until you have proven there is a short on that side, which can easily be done by checking across the capacitors with a DMM. Most of the caps are in parallel, so if you do find a short then report back to get some help on finding the defective one.

I didn't find any short on the capacitors (continuity only in one side).

For doing the tape this video covers it quite well and it just happens to be a TCL 55 inch.

https://www.youtube.com/watch?v=pfrRhw7-ZII

When i add a tape to a part of the ribbon cable, half of the screen works but no image in the other one (where there is the problem).

Ref of the panel: ST5461D04-1-XL-3

thanks for your help.

[deep000]

Re: TCL 55p1us turns ON with sound and black screen

After some trials with the tape, i got the second half to work but the image is darker than the other half.
I will try now to cover less lines.

What can i test on the panel to track down the problem ? capacitors seems good.

[deep000]

Re: TCL 55p1us turns ON with sound and black screen

After some trials with the tape, i got the second half to work but the image is darker than the other half.
I will try now to cover less lines.

What can i test on the panel to track down the problem ? capacitors seems good.

After several tests, the second half is still darker and all the screen becomes worse with time.



I did some additional voltage tests:

TCON:
- VGH 20V

PANEL:
1- L 13.7 mv
2- R 3.87 V
3- DOT_C 2.99 V
4- VDD33 3.3 V
5- CKV 1.46 V
6- STVR 11.4 mv
7- OE 3.28 V
8- STV 12.5 mv
9- SPI DCK 9.7 mv
10- SPI DI 9.8 mv
11- SPI HOLD 3.27 V
12- Spi VDD 3.30 V

[RDC55]

Re: TCL 55p1us turns ON with sound and black screen

So what pin numbers and which connector are covered in tape. Don't cover any pins that are not common to connectors CN2 and CN3. I usually start by taking a DMM and finding a group that are common between the two connectors.

How clear is the video when the bad side is disconnected? Post a pic

[deep000]

Re: TCL 55p1us turns ON with sound and black screen

So what pin numbers and which connector are covered in tape. Don't cover any pins that are not common to connectors CN2 and CN3. I usually start by taking a DMM and finding a group that are common between the two connectors.

How clear is the video when the bad side is disconnected? Post a pic

The video is very good.
Do i need to test for continuity between the pins of each connector (1-1, 2-2 ...) ?

[RDC55]

Re: TCL 55p1us turns ON with sound and black screen

The video is very good.
Do i need to test for continuity between the pins of each connector (1-1, 2-2 ...) ?

Not necessarily, you are looking for common pins that when that group is taped on the bad side the TV comes to life on both sides. They are normally near the ends but it is common for say 80 on one connector to connect to 1 on the other because the buffer boards are somewhat mirrored to each other. Once you find the group of pins then it just becomes a process to determine if you can bring both halves back to life with quality video.

In the video he was lucky enough to have some common pins labeled and was able to follow the etch. I use a meter because sometimes it's not that easy to follow the etch to find the common pins.

In a perfect world we would have schematics showing the hookup and then you could just follow the lines to the gate drivers, which are the only ones viable for repair with tape. If you have bad source drivers it's game over and the TV would have to be scrapped.

The other option is if this set has COF on the side is removing all of them on the bad side. There is a very detailed thread on that process on this site. A lot of the newer sets have the gate drivers built into the LCD panel.

[gpatadia]

hi guys
can anyone upload working st5461d04-1-c-1 board eprom dump
thanks