Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > Troubleshooting TVs and Video Sources
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 10-19-2019, 10:53 PM   #1
Stuckster
Member
 
Join Date: Oct 2019
City & State: Sydney
My Country: Australia
I'm a: Knowledge Seeker
Posts: 30
Default Backlights but no picture - No 12v to Tcon board

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
Attached Images
File Type: jpg full layout.jpg (517.3 KB, 16 views)
File Type: jpg MB to Tcon.jpg (706.4 KB, 15 views)
File Type: jpg Mainboard.jpg (797.8 KB, 18 views)
File Type: jpg Tcon.jpg (740.9 KB, 15 views)
File Type: jpg PCB.jpg (736.6 KB, 14 views)
File Type: jpg LED Driver.jpg (610.6 KB, 10 views)
Stuckster is offline   Reply With Quote
Old 10-19-2019, 11:25 PM   #2
neilc6
Badcaps Veteran
 
Join Date: Nov 2015
City & State: BC
My Country: Canada
I'm a: Knowledge Seeker
Posts: 604
Default 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.

Last edited by neilc6; 10-19-2019 at 11:27 PM..
neilc6 is offline   Reply With Quote
Old 10-20-2019, 12:32 AM   #3
Stuckster
Member
 
Join Date: Oct 2019
City & State: Sydney
My Country: Australia
I'm a: Knowledge Seeker
Posts: 30
Default Re: Backlights but no picture - No 12v to Tcon board

Here is a pic of the Mainboard without the heatsink cover.
Attached Images
File Type: jpg IMG_20191020_145702089.jpg (1.05 MB, 14 views)
Stuckster is offline   Reply With Quote
Old 10-20-2019, 12:33 AM   #4
Stuckster
Member
 
Join Date: Oct 2019
City & State: Sydney
My Country: Australia
I'm a: Knowledge Seeker
Posts: 30
Default Re: Backlights but no picture - No 12v to Tcon board

Thanks. Tried what you suggested but unfortunately no change.
Stuckster is offline   Reply With Quote
Old 10-20-2019, 01:17 AM   #5
neilc6
Badcaps Veteran
 
Join Date: Nov 2015
City & State: BC
My Country: Canada
I'm a: Knowledge Seeker
Posts: 604
Default 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.

Last edited by neilc6; 10-20-2019 at 01:18 AM..
neilc6 is offline   Reply With Quote
Old 10-20-2019, 02:19 AM   #6
Stuckster
Member
 
Join Date: Oct 2019
City & State: Sydney
My Country: Australia
I'm a: Knowledge Seeker
Posts: 30
Default Re: Backlights but no picture - No 12v to Tcon board

Quote:
Originally Posted by neilc6 View Post
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.

Quote:
Originally Posted by neilc6 View Post
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?

Quote:
Originally Posted by neilc6 View Post
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?
Stuckster is offline   Reply With Quote
Old 10-20-2019, 05:45 AM   #7
diif
Badcaps Veteran
 
Join Date: Feb 2014
City & State: Midlands
My Country: England
I'm a: Professional Tech
Posts: 4,257
Default 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.
diif is offline   Reply With Quote
Old 10-20-2019, 10:05 PM   #8
budm
Badcaps Veteran
 
budm's Avatar
 
Join Date: Feb 2010
City & State: S.F. Bay area
My Country: USA
Line Voltage: 120V 60Hz
I'm a: Knowledge Seeker
Posts: 36,265
Default 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.
__________________
Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956

Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999

Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl

Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/

TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
budm is offline   Reply With Quote
Old 10-21-2019, 06:24 AM   #9
Stuckster
Member
 
Join Date: Oct 2019
City & State: Sydney
My Country: Australia
I'm a: Knowledge Seeker
Posts: 30
Default Re: Backlights but no picture - No 12v to Tcon board

Quote:
Originally Posted by budm View Post
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.
Attached Images
File Type: jpg IMG_5566.jpg (1,001.2 KB, 20 views)
File Type: jpg IMG_5565.jpg (966.4 KB, 14 views)
Stuckster is offline   Reply With Quote
Old 10-23-2019, 12:44 AM   #10
Stuckster
Member
 
Join Date: Oct 2019
City & State: Sydney
My Country: Australia
I'm a: Knowledge Seeker
Posts: 30
Default Re: Backlights but no picture - No 12v to Tcon board

Quote:
Originally Posted by diif View Post
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.
Stuckster is offline   Reply With Quote
Old 10-23-2019, 02:51 AM   #11
diif
Badcaps Veteran
 
Join Date: Feb 2014
City & State: Midlands
My Country: England
I'm a: Professional Tech
Posts: 4,257
Default Re: Backlights but no picture - No 12v to Tcon board

Quote:
Originally Posted by Stuckster View Post
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.
diif is offline   Reply With Quote
Old 10-23-2019, 03:29 AM   #12
dick_barton
Badcaps Veteran
 
dick_barton's Avatar
 
Join Date: Aug 2015
City & State: Cardiff
My Country: Wales
Line Voltage: 230V AC, 50Hz
I'm a: Hobbyist Tech
Posts: 4,900
Default Re: Backlights but no picture - No 12v to Tcon board

What is the part number given on the IC
Attached Images
File Type: jpg IMG_20191020_145702089.jpg (1.90 MB, 11 views)
__________________
Willing to help but I'm no expert.
dick_barton is offline   Reply With Quote
Old 10-23-2019, 03:38 AM   #13
Stuckster
Member
 
Join Date: Oct 2019
City & State: Sydney
My Country: Australia
I'm a: Knowledge Seeker
Posts: 30
Default Re: Backlights but no picture - No 12v to Tcon board

Quote:
Originally Posted by dick_barton View Post
What is the part number given on the IC
Hi. Thanks for your help! It should be much clearer on this image.
https://badcaps.net/forum/attachment...6&d=1571657047
Stuckster is offline   Reply With Quote
Old 10-23-2019, 03:41 AM   #14
nomoresonys
Badcaps Veteran
 
Join Date: Jan 2013
City & State: midwest
My Country: U.S.
I'm a: Knowledge Seeker
Posts: 4,082
Default 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?

Last edited by nomoresonys; 10-23-2019 at 04:11 AM..
nomoresonys is offline   Reply With Quote
Old 10-23-2019, 04:02 AM   #15
nomoresonys
Badcaps Veteran
 
Join Date: Jan 2013
City & State: midwest
My Country: U.S.
I'm a: Knowledge Seeker
Posts: 4,082
Default 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 is offline   Reply With Quote
Old 10-23-2019, 04:09 AM   #16
nomoresonys
Badcaps Veteran
 
Join Date: Jan 2013
City & State: midwest
My Country: U.S.
I'm a: Knowledge Seeker
Posts: 4,082
Default 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 is offline   Reply With Quote
Old 10-23-2019, 04:54 AM   #17
nomoresonys
Badcaps Veteran
 
Join Date: Jan 2013
City & State: midwest
My Country: U.S.
I'm a: Knowledge Seeker
Posts: 4,082
Default 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.
nomoresonys is offline   Reply With Quote
Old 10-23-2019, 05:06 AM   #18
dick_barton
Badcaps Veteran
 
dick_barton's Avatar
 
Join Date: Aug 2015
City & State: Cardiff
My Country: Wales
Line Voltage: 230V AC, 50Hz
I'm a: Hobbyist Tech
Posts: 4,900
Default Re: Backlights but no picture - No 12v to Tcon board

Quote:
Originally Posted by Stuckster View Post
Hi. Thanks for your help! It should be much clearer on this image.
https://badcaps.net/forum/attachment...6&d=1571657047
Unfortunately it's not. It's the numbers written on top of the IC I'm asking for.
dick_barton is offline   Reply With Quote
Old 10-23-2019, 05:22 AM   #19
Stuckster
Member
 
Join Date: Oct 2019
City & State: Sydney
My Country: Australia
I'm a: Knowledge Seeker
Posts: 30
Default Re: Backlights but no picture - No 12v to Tcon board

Quote:
Originally Posted by nomoresonys View Post
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.

Last edited by Stuckster; 10-23-2019 at 05:28 AM..
Stuckster is offline   Reply With Quote
Old 10-23-2019, 05:37 AM   #20
Stuckster
Member
 
Join Date: Oct 2019
City & State: Sydney
My Country: Australia
I'm a: Knowledge Seeker
Posts: 30
Default Re: Backlights but no picture - No 12v to Tcon board

Quote:
Originally Posted by dick_barton View Post
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?
Stuckster is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2019
Powered by vBulletin ®
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 05:19 PM.
Did you find this forum helpful?