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 07-01-2016, 01:55 PM   #1
madcow007
New Member
 
Join Date: Nov 2010
Posts: 10
Default LG 70LB7100 no backlight after 2-5 min

I have a LG 70LB7100 just a few months out of warranty. When I power the set on it works perfectly for 2-5 minutes then the backlight will go out and audio will remain. I can power cycle the tv again and backlight returns.

The tv is currently wall mounted so I'm unable to take photos of the boards until I get some help to remove it. I was wondering if anyone could recommend some trouble shooting steps to determine if its the power supply or the LED,s.

Thanks
madcow007 is offline   Reply With Quote
Old 07-01-2016, 02:20 PM   #2
budwich
Badcaps Veteran
 
Join Date: Jul 2015
City & State: Kanata Ontario
My Country: Canada
I'm a: Knowledge Seeker
Posts: 2,589
Default Re: LG 70LB7100 no backlight after 2-5 min

Put on a uniform "color" test screen (preferably white) and see if you can see any issues on the screen before it goes out.
budwich is offline   Reply With Quote
Old 07-01-2016, 02:31 PM   #3
madcow007
New Member
 
Join Date: Nov 2010
Posts: 10
Default Re: LG 70LB7100 no backlight after 2-5 min

Budwich just ran the test with a white image and I seen no distortion then at around the 3 minute mark the backlights shut off.
madcow007 is offline   Reply With Quote
Old 07-01-2016, 03:13 PM   #4
ReeceyBurger123
Never Give Up !
 
ReeceyBurger123's Avatar
 
Join Date: May 2014
City & State: Telford
My Country: Britain
Line Voltage: 240 VAC 50Hz
I'm a: Student Tech
Posts: 7,124
Default Re: LG 70LB7100 no backlight after 2-5 min

Theres a fault likely in the Led strings possibly with the little connectors that join the Leds breaking down. Check the threads about testing the return line voltage for the Leds see if you can spot anything thats an issue.
__________________
Please Do Not PM My Page Asking For Help Badcaps Is The Place For Advise, Page Linked For Business Reasons Only. Anyone Doing So Will Be Banned Instantly !

https://www.facebook.com/Telford-Tel...7894576335359/
ReeceyBurger123 is offline   Reply With Quote
Old 07-04-2016, 07:57 AM   #5
madcow007
New Member
 
Join Date: Nov 2010
Posts: 10
Default Re: LG 70LB7100 no backlight after 2-5 min

ReeceyBurger123 thanks for the reply I finally got the set down today I can see proper 52v until shutdown the area on the pcb where the fets are located look a bit brown from the top side and it feels warm to the touch after shut down but not HOT

Photos attached please excuse typos and wall of txt I'm on mobile.
Attached Images
File Type: jpg tmp_18245-20160704_094949889524069.jpg (562.5 KB, 90 views)
File Type: jpg tmp_18245-20160704_094959-1931334489.jpg (544.5 KB, 76 views)
madcow007 is offline   Reply With Quote
Old 07-04-2016, 10:23 AM   #6
jetadm123
Badcaps Veteran
 
Join Date: Feb 2010
City & State: California
Posts: 2,169
Default Re: LG 70LB7100 no backlight after 2-5 min

When the set is up and running, you can try heating up the fets with a hair dryer to see if you can accelerate the backlight shutting down. If you're lucky, it might be a failing fet or a bad solder joint. Otherwise, it might be as Reecey suggested.
jetadm123 is offline   Reply With Quote
Old 07-04-2016, 10:29 AM   #7
ReeceyBurger123
Never Give Up !
 
ReeceyBurger123's Avatar
 
Join Date: May 2014
City & State: Telford
My Country: Britain
Line Voltage: 240 VAC 50Hz
I'm a: Student Tech
Posts: 7,124
Default Re: LG 70LB7100 no backlight after 2-5 min

Remove the Pcb and inspect for bad solder joints in that hot area.
ReeceyBurger123 is offline   Reply With Quote
Old 07-04-2016, 03:00 PM   #8
madcow007
New Member
 
Join Date: Nov 2010
Posts: 10
Default Re: LG 70LB7100 no backlight after 2-5 min

Thanks for the reply guys I stressed the fets with a hair dryer and it seemed to quicken the time to shutdown. I didnt see any bad solder joints the set belongs to a friend and he is impatient so he decided to order a new power supply will update when it arrives.
madcow007 is offline   Reply With Quote
Old 07-04-2016, 05:03 PM   #9
jetadm123
Badcaps Veteran
 
Join Date: Feb 2010
City & State: California
Posts: 2,169
Default Re: LG 70LB7100 no backlight after 2-5 min

Just a suggestion: While you're waiting for a new supply, grab a soldering iron and touch up all the joints on those mosfets with some fresh solder. If that fixes the problem, then maybe return the supply you bought?
jetadm123 is offline   Reply With Quote
Old 07-04-2016, 06:01 PM   #10
ReeceyBurger123
Never Give Up !
 
ReeceyBurger123's Avatar
 
Join Date: May 2014
City & State: Telford
My Country: Britain
Line Voltage: 240 VAC 50Hz
I'm a: Student Tech
Posts: 7,124
Default Re: LG 70LB7100 no backlight after 2-5 min

Maybe get us an image of the bottom side of the Pcb ? Sounds like cold solder joints to me would have been a good idea to do that before ordering a part IMO but your on the right track at least
ReeceyBurger123 is offline   Reply With Quote
Old 07-14-2016, 12:33 PM   #11
thelmores
New Member
 
Join Date: Feb 2011
Posts: 17
Default Re: LG 70LB7100 no backlight after 2-5 min

FWIW, have identical set that has same problem.

Replacing main and power supply did not fix problem. Almost certainly a panel issue.

Customer said he is going to donate the set, so we are going to see what we can learn. never disassembled panel before.....
thelmores is offline   Reply With Quote
Old 07-14-2016, 01:36 PM   #12
ReeceyBurger123
Never Give Up !
 
ReeceyBurger123's Avatar
 
Join Date: May 2014
City & State: Telford
My Country: Britain
Line Voltage: 240 VAC 50Hz
I'm a: Student Tech
Posts: 7,124
Default Re: LG 70LB7100 no backlight after 2-5 min

Hmm sounds like the Led string connectors or even the Leds then buddy. Is this Edge lit or full array ? Also if you take the screen apart be very care of the glass it cracks easy.
ReeceyBurger123 is offline   Reply With Quote
Old 09-15-2016, 04:01 AM   #13
DrewBeer
New Member
 
Join Date: Sep 2016
City & State: Orange County, Ca
My Country: United States
I'm a: Knowledge Seeker
Posts: 1
Default Re: LG 70LB7100 no backlight after 2-5 min

I'm glad i found this thread. Have the same problem with my 70LB7100. Just replaced the power supply, same problem, Sometimes it works for a few hours, and sometimes its a few minutes.

I haven't taken it down past the back panel, but i guess i might as well start digging. Did anyone get further with this problem?
DrewBeer is offline   Reply With Quote
Old 01-20-2017, 07:48 AM   #14
Help
New Member
 
Join Date: Dec 2016
City & State: Kingshill St Croix
My Country: Virgin Islands
I'm a: Knowledge Seeker
Posts: 2
Default Re: LG 70LB7100 no backlight after 2-5 min

Any update to this problem?
Help is offline   Reply With Quote
Old 01-20-2017, 08:00 AM   #15
Help
New Member
 
Join Date: Dec 2016
City & State: Kingshill St Croix
My Country: Virgin Islands
I'm a: Knowledge Seeker
Posts: 2
Default Re: LG 70LB7100 no backlight after 2-5 min

Did you look into the issue with lg70lb7100 no backlight when you got customer TV?
Help is offline   Reply With Quote
Old 07-18-2017, 09:12 PM   #16
gavric
Member
 
Join Date: Jun 2011
Posts: 37
Default Re: LG 70LB7100 no backlight after 2-5 min

Bump

Interested in any update to this, going thru same issue.
I actually opened screen up and glued up some led bulbs lenses that fell off and made bright spots on the screen and seen that one of the led strips was not lighting up. It was odd because first 8 leds were out then last 8 would work. power comes from side that is on non working leds side. Its exactly half of string 8 bulbs that are out of 16 in a row. There is 8 rows on leds. I messed with it some and led string came alive. I left tv on for a while, no problem. Tv worked for long time and all leds worked.

When I finally assembled tv without breaking glass tv decided to start shutting down random led strings on right side of screen only, sometimes after 15 minutes, sometimes 5, sometimes 2 minutes. Power cycling instantly turns screen nice and bright and all leds work until it acts up again. Each row of leds is separately powered by its own power input with three wires + - -, 52 VDC. Power supply looks burned up some just like poster above.

I did not trouble shoot power supply yet because i am so pissed of at it.
Anyone solved it?
gavric is offline   Reply With Quote
Old 10-09-2018, 06:49 AM   #17
bult
New Member
 
Join Date: Jun 2016
City & State: Skellefteć
My Country: Sweden
Line Voltage: 240VAC 50Hz
I'm a: Knowledge Seeker
Posts: 2
Default Re: LG 70LB7100 no backlight after 2-5 min

Bump!

I would also know if anyone of you solved this issue with this model? I have the exactly same issue with mine. Backlight stays on for a while and then goes black. I was just about to order a new powerboard but then I stumbled upon this thread... So before i take the panel apart i would be nice to know if it is worth the effort.

Thanks!
bult is offline   Reply With Quote
Old 10-09-2018, 10:14 AM   #18
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: 38,511
Default Re: LG 70LB7100 no backlight after 2-5 min

I would try lowing the Backlights level to as low as possible first to see if the backlights will stay on longer.
Providing the pictures of the whole backside of the TV showing all the boards will also help so we can see what we are dealing with.
__________________
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

Last edited by budm; 10-09-2018 at 10:16 AM..
budm is offline   Reply With Quote
Old 10-09-2018, 12:44 PM   #19
truep
Badcaps Veteran
 
Join Date: Aug 2010
City & State: Flower mound, TX
My Country: USA
Line Voltage: 120VAC 60 HZ
I'm a: Knowledge Seeker
Posts: 362
Default Re: LG 70LB7100 no backlight after 2-5 min

As a general rule, NEVER run the backlights at 100% I set mine at 75, MAX of 80%. set it around 70% and it may work fine for a while. ( my 65" lasted 2 years till I found a new LED strip.
truep is offline   Reply With Quote
Old 10-09-2018, 12:55 PM   #20
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: 38,511
Default Re: LG 70LB7100 no backlight after 2-5 min

BTW, turn them down on ALL inputs.
budm 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 - 2020
Powered by vBulletin ®
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 10:54 AM.
Did you find this forum helpful?