Panasonic LED TV TC-40A420U - Replaced Backlight LEDs but now no image/display or garbled

[Diah]

Ok, I understand now. I also can use a dedicated variable bench power supply to power the panel. How may amps does it draw?

wrong... you don't need any external.... we need to use the TV power supply 12V,,, then when you power on the set the LED BL will come on so you can see the panel clearly if there are issue.

[signal.quest]

Ok, I understand now. I also can use a dedicated variable bench power supply to power the panel. How may amps does it draw?

[Diah]

If I disconnect the LVDS cable from the main board to the panel then I will have no power connection to the panel - is that correct?
I only have 1 cable that connects to the panel. I have previously used my meter and found 12V on the panel when the cable was connected. I know the panel board is getting power.

we know the panel power right now come via LVDS... this why i wrote disconnect the LVDS and power the panel fuse FP1 with 12V direct from the power boards.... this is test for panel.to have color pattern

[signal.quest]

If I disconnect the LVDS cable from the main board to the panel then I will have no power connection to the panel - is that correct?
I only have 1 cable that connects to the panel. I have previously used my meter and found 12V on the panel when the cable was connected. I know the panel board is getting power.

[Diah]

yours T-CON are interrogated with the Panel buffer boards. to test the panel.. you need
disconnect the LVDS cable between main boards and Panel , check on the PSU test point at Cold Area the 12V rail...
fed the Panel T-CON boards with 12V direct to fuse FP1 from the rail you found on PSU .. turn on the Tv and check the screen.

Notice. be sure the panel buffer boards had connect point to TV chassis

[signal.quest]

I assume then, the issue is something with the LCD panel? Are there common troubles with this type of panel? Or did I likely damage it from dismantling it to replace the LED backlights? I will try the troubleshooting steps you mentioned. What is the name of the integrated board to the LCD panel called? Is that the TCON or just LCD panel circuit board?

[Diah]

Thanks. I will try that test. Do you think my logic (A) board is OK since it is recognized when laptop is connected to HDMI? Is there any other way to verify it is OK?

yes its fine..

[signal.quest]

Thanks. I will try that test. Do you think my logic (A) board is OK since it is recognized when laptop is connected to HDMI? Is there any other way to verify it is OK?

[Diah]

this look for me Damage at LVDS

[Diah]

the crimped/bent cable.are normal,way to use for changing cable direction.

you can try just disconnect the 2 on the right side of the U ribbon ( yellow mark ) and turn on the tv,, see if the screen will display half picture

to check cable with DM. need to set the DM on peep ton option and check the pins of the socket from MB to panel one by one for connectivity

[signal.quest]

Here are the photos of the crimped/bent cable.

[signal.quest]

I just checked all connection cable contact pins with a jeweler loop and I don't see any problem areas. The cable does has 2 bends/crimps in it that you can see from the photo. I suspect it was always like that but it is possible it got crimped when I had the TV dismantled and laying for weeks waiting for replacement LED shipment to arrive. Is there a way I can verify there are no breaks in the cable using a meter? Are those bends/crimps common or does it look like I made a mistake? Thanks.

[Diah]

under good magnifier check the contact pins of the LVDS cable at main boards side
the one to panel with red and yellow mark need to check if there any cut at the cable side..
the other U ribbon on panel buffer boards ( yellow ) check the contact pins too.

[signal.quest]

Thank you for the reply. I am in process of checking the panel board for obvious issues, therefore it has been partially disassembled. But I have connected it back to show the critical connections (not speakers or indicator light). Thanks. Please see the photos. Thanks.

[Diah]

show us the back of the tv of all boards to see how they are connected to each other

[signal.quest]

Some additional information:
Panel is Innolux v400HJ6-ME2 Rev C1

Logic/Mainboard/A Board:
TXN/A1YZUUS (TNP4G565)

Power (P) Board:
TXN/P1AEVUS (TNPA6029)

Please help me verify Panel or Mainboard is OK. Thanks.

[signal.quest]

I have a Panasonic LED TV TC-40A420U. The TV was given to me as an attempt to fix or throw out. I replaced the Backlight LEDs and now the screen lights up, but there is no image/display. If I play with the up/down buttons I can get the display to change from black to garbled. I can't get sound from HDMI but not sure of what input is selected. I have no remote control. When I connect a laptop to the HDMI ports it recognizes a Panasonic TV for display and sound output but I can't see or hear anything through the TV. This makes me think the mainboard is OK, but not sure if mainboard can partially fail? I am hoping it is not a panel issue, but maybe I damaged it by dismantling all of the layers. It was my first attempt at LED backlight repair. I also was delicate with the panel circuit board, but I am concerned about it. Please see the pictures for what display shows. Any help is appreciated. Thanks.