Backlights but no picture - No 12v to Tcon board

[Stuckster]

Hi all,

First time poster.
Hoping to get some help troubleshooting my 65" TCL.

Model: U65E5800FS (AUS)
D65A620U (China Equivalent)

Symptoms: Backlight but no picture/display.

I have already determined:
- Tcon board not receiving any 12V.
- Mainboard only outputting 2.6v to audio/speakers
- Replacement PCB (no change)
- Replacement Tcon board (no change)

- Voltages from PCB to Mainboard (with TV on) read
1. VPWR 23.6v
2. VPWR 23.6v
3. GND 0v
4. VPWR 23.6v
5. GND 0v
6. GND 3.2v
7. VSTB 3.3v
8. 3DEN 1.0v
9. GND 0v
10. P/O 3.2v
11. PDIM 3.2v
12. BL ON 3.2v

Interestingly there is doesn't seem to be any 12V going to or from the PCB to the mainboard. The panel has a dedicated LED driver module which is receiving voltage to turn on the backlights. But where is the 12v for the Tcon board meant to come from?

Pics attached.

Any help would be much appreciated.

I need to be 100% certain which board is faulty before I outlay money to replace it. I'm in Australia and unlike in the US, with shops like shopjimmy.com, spare parts are quite expensive to source privately. eg: $300 for a mainboard.

cheers

[neilc6]

Re: Backlights but no picture - No 12v to Tcon board

With tv unplugged, disconnect ribbon cable from tcon to panel one side at a time and see if tv powers up one side. But if you're not receiving 12V to the tcon, its usually switched from the main board.

[Stuckster]

Re: Backlights but no picture - No 12v to Tcon board

Here is a pic of the Mainboard without the heatsink cover.

[Stuckster]

Re: Backlights but no picture - No 12v to Tcon board

Thanks. Tried what you suggested but unfortunately no change.

[neilc6]

Re: Backlights but no picture - No 12v to Tcon board

12V for the tcon usually is switched through the main board from the power supply on one of the edges of the LVDS cables. You can usually figure out which edge by ohming the tcon fuse with one of the edges and usually passes through more than 1 pin. You can trace this through the main board where it should go through a FET switch. Could be a BGA failure on the processor not sending the tcon on signal to the FET. Can test this by heating the processor with a hair dryer before plugging in. Also check for 12V from the power supply going to the main board.

[Stuckster]

Re: Backlights but no picture - No 12v to Tcon board

12V for the tcon usually is switched through the main board from the power supply on one of the edges of the LVDS cables. You can usually figure out which edge by ohming the tcon fuse with one of the edges and usually passes through more than 1 pin.

From memory I think it's the last 4 pins on the 51 pin cable. So I should be able to check this easily enough.

You can trace this through the main board where it should go through a FET switch. Could be a BGA failure on the processor not sending the tcon on signal to the FET. Can test this by heating the processor with a hair dryer before plugging in.

Looks like there are two processors on the board. Which one would I heat?

Also check for 12V from the power supply going to the main board.

Yeah I can't see any, which is odd (see the list of voltage readings from the original post). In the absence of a dedicated 12v signal going direct from the pcb to the MB, is it possible that the mainboard could convert the 23.6v or the 3v into 12v?

[diif]

Re: Backlights but no picture - No 12v to Tcon board

It will be 24v -> 12v. You could check the coils (grey squares) for a short to ground, the power rails for the processors and memory will be low but it's possible the 12v might have a short.

[budm]

Re: Backlights but no picture - No 12v to Tcon board

https://www.badcaps.net/forum/attach...1&d=1571549151
Can we get picture that is in focus? Right now I cannot read the designators on the board.

[Stuckster]

Re: Backlights but no picture - No 12v to Tcon board

https://www.badcaps.net/forum/attach...1&d=1571549151
Can we get picture that is in focus? Right now I cannot read the designators on the board.

Hi BudM
Sorry. My mobile is hopeless with close up detail. I've retaken using a proper camera and split it into two photos so you get clearer detail. Thanks.

[Stuckster]

Re: Backlights but no picture - No 12v to Tcon board

It will be 24v -> 12v. You could check the coils (grey squares) for a short to ground, the power rails for the processors and memory will be low but it's possible the 12v might have a short.

Unfortunately no shorts to ground in the coils.
There is a 6R8 coil on the mainboard reading 12v. It also has a test point on the flip side that says 12v. But somehow that isn't getting to the Tcon.

[diif]

Re: Backlights but no picture - No 12v to Tcon board

Unfortunately no shorts to ground in the coils.
There is a 6R8 coil on the mainboard reading 12v. It also has a test point on the flip side that says 12v. But somehow that isn't getting to the Tcon.

12v on a test point sounds hopeful, it will need tracing to see where it goes.

[dick_barton]

Re: Backlights but no picture - No 12v to Tcon board

What is the part number given on the IC

[Stuckster]

Re: Backlights but no picture - No 12v to Tcon board

What is the part number given on the IC

Hi. Thanks for your help! It should be much clearer on this image.
https://www.badcaps.net/forum/attach...6&d=1571657047

[nomoresonys]

Re: Backlights but no picture - No 12v to Tcon board

Meter in diode mode check the small ceramic capacitors on t-con, see if any read short or beep if you have beep function on meter, kind of unlikely tho, see if tcon fuse is blown, do you get the 12 volt with the lvds cable disconnected?

[nomoresonys]

Re: Backlights but no picture - No 12v to Tcon board

Check for voltage on each side of tcon fuse black probe on chassis ground if you haven't yet.

[nomoresonys]

Re: Backlights but no picture - No 12v to Tcon board

Could try heating the mainboard a small section at a time with a hairdryer, hit the whole board including the ceramic and electrolytic caps, see if display changes any.

[nomoresonys]

Re: Backlights but no picture - No 12v to Tcon board

Unhook ribbon cables from t-con to panel then see if you have voltage on tcon.

[dick_barton]

Re: Backlights but no picture - No 12v to Tcon board

Hi. Thanks for your help! It should be much clearer on this image.
https://www.badcaps.net/forum/attach...6&d=1571657047

Unfortunately it's not. It's the numbers written on top of the IC I'm asking for.

[Stuckster]

Re: Backlights but no picture - No 12v to Tcon board

Meter in diode mode check the small ceramic capacitors on t-con, see if any read short or beep if you have beep function on meter, kind of unlikely tho, see if tcon fuse is blown, do you get the 12 volt with the lvds cable disconnected?

Tcon fuse is good. I believe the 12v is sent to the Tcon via the 51pin LVDS cable. So I would presume that there will still be no 12v with the LVDS unplugged, but I will test it anyway.

[Stuckster]

Re: Backlights but no picture - No 12v to Tcon board

Unfortunately it's not. It's the numbers written on top of the IC I'm asking for.

Hey. Sorry. I can see 2 or 3 smaller ICs on the board. Do you need to know the numbers printed on each of them? If not, could you identify the specific one you are referring to?