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Equipment Repairs => LCD TV forum => Topic started by: rubbishrat on March 21, 2012,15:06:12

Title: LG 42LC55 board No EAY38640201 Backlight flashover, any help appreciated
Post by: rubbishrat on March 21, 2012,15:06:12

Hi all, my first time posting here! I used to repair TVs for a living years ago but I'm retired now, I've been given an old LG 42LC55 that will start briefly and shut down after a second or so, the picture looks OK when its on, I'm new to this computer and LCD tech so please be patient with me. During the brief time the set starts up there is high voltage flashover from one of the backlight leads to chassis, a bit like we used to see when the eht trippler failed. I didn't expect to see this and I can't find any faulty components checking cold. all the semiconductors check out fine, the lt caps esr all check ok. could this be the ballast transformer ?? or maybe the FAN7382 driver chip ?this main power board includes the backlight components. Any help appreciated. Cheers, Pete   

Title: Re: LG 42LC55 board No EAY38640201 Backlight flashover, any help appreciated
Post by: sparky on March 22, 2012,02:53:52

hi
check the caps on psu they can cause this  some show signs
of bulging
dave

Title: Re: LG 42LC55 board No EAY38640201 Backlight flashover, any help appreciated
Post by: watteau on March 22, 2012,03:39:07

Hello,
There is a service bulletin for intermittent problems
on this model (ceratec filters), this might be causing the problem.
If you search previous posts using 'ceratec' you should find
more info.
Regards,
John.

Title: Re: LG 42LC55 board No EAY38640201 Backlight flashover, any help appreciated
Post by: Turnip on March 25, 2012,12:03:24

Hi Pete,

Curious one - never seen flashover from backlight leads to chassis or tube insulation problems with anything bigger than a 24 inch (where it's common with top/bottom tubes in metal housings)

Guess some PS over voltage prob where inverter shuts down sensing fault - Chris.

Title: Re: LG 42LC55 board No EAY38640201 Backlight flashover, any help appreciated
Post by: sparky on March 25, 2012,14:51:12

hi
if you can split the screen you should see were
 the connecters have been arcing and burning
dave

Title: Re: LG 42LC55 board No EAY38640201 Backlight flashover, any help appreciated
Post by: rubbishrat on March 28, 2012,18:52:08

Many thanks to all who replied, a quick update, I have replaced all electrolytics (19 of them) but no change in symptoms. set shuts down before I can properly check lt rails but I haven't found anything bad so far. I disconnected the speakers and watched in darkness but the lower ht lead leaks to chassis both ends where it enters the steel channel and where it exits. Set shuts down in about 1 sec.  Overvoltage seems to be the answer, I will keep looking and post further news if any. Thanks again, Pete.