lg 26LC2R lcd tv backlight turns off

[anno]

hi.
i have a lg 26LC2R lcd tv which backlight is turning off. there is 24v going to the inverter. when backlight off still 24v present. BL-ON voltage good too.

so i think there is a fault with the inverter or lamps. But I'm not familiar with these kind of inverters. I think it's EEFL. don`t know how to troubleshoot.
anyone have suggestion=

[multimeter]

Re: lg 26LC2R lcd tv backlight turns off

post up good quality pics,of ,inverter,psu,mainboard,showing the connectors also

[anno]

Re: lg 26LC2R lcd tv backlight turns off

here are some pictures

[budm]

Re: lg 26LC2R lcd tv backlight turns off

So the backlights did come on for seconds?

[multimeter]

Re: lg 26LC2R lcd tv backlight turns off

does voltage REMAIN at 3.4vON pin(INV_ON) when backlights go off?

[anno]

Re: lg 26LC2R lcd tv backlight turns off

the backlight is on for 2 seconds then off. The Inv_On voltage remain 3.4v

[multimeter]

Re: lg 26LC2R lcd tv backlight turns off

im wondering wether there are no feedback circuits on the inverter,sending back an error signal to the main board to shut itself down,so the inverter stays powerd up,and isnt detecting faully ccfl tube fail

the tubes??

[anno]

Re: lg 26LC2R lcd tv backlight turns off

i think feedback signal goes to IC on inverter. but maybe there is a bad tube. i have a look at them

[tom66]

Re: lg 26LC2R lcd tv backlight turns off

Do you have a neon bulb lying around? The kind of thing in old plug strips...
It glows in presence of HV. I have used one before to see which of master or slave is not working

[budm]

Re: lg 26LC2R lcd tv backlight turns off

Those two caps on both inverter boards are good? Try heating them with hair dryer, also those MOSFETs and the resistance of the high voltage windings of both transformers should be checked.

[anno]

Re: lg 26LC2R lcd tv backlight turns off

i checked the components on the inverter, but could'nt find a fault. i try heating.
and i try to find a neon bulb

[budm]

Re: lg 26LC2R lcd tv backlight turns off

I use this:
http://s807.photobucket.com/user/bud...tml?sort=3&o=0

http://s807.photobucket.com/user/bud...tml?sort=3&o=1

http://s807.photobucket.com/user/bud...tml?sort=3&o=1

[anno]

Re: lg 26LC2R lcd tv backlight turns off

budm: ok. only 1 wire is needed and you hold to output of inverter socket?

i have more problems now. the power supply clicking on/off , i don`t know if its related to inverter fault or another fault *sigh*.

it seems that I myself bring additional difficulties in. grrr

[sam_sam_sam]

Re: lg 26LC2R lcd tv backlight turns off

You need to hook both wire to the neon bulb just like the tubes are hook up

Also you may have more than one tube that is bad

Also I think that the four IC chip that are very close to the transformer might be mosfet

Take the # that are on the chips and Google them and see if they are mosfet if they are check and see if any are shorted I had a LCD monitor that had this problem and after replacing them it started working again

[budm]

Re: lg 26LC2R lcd tv backlight turns off

"i checked the components on the inverter, but could'nt find a fault" So those 4 MOSFETs checked out OK, P/N?

[anno]

Re: lg 26LC2R lcd tv backlight turns off

The mosfets P/N is 8958a (FDS8958A) dual mosfets. i used diode setting on multimeter and got 0.45v from drain to source on all fets both inverters.

i not really sure know how to test the transformers. the pins to the left show 0,2 ohm ? don`t know what pins are secundairy. but now i have other problems, the power supply relay is clicking on/off. The ps-on signal is not stable. I have tested the PSU standalone. All voltages are present, but 12v line a little bit low 11.5V and when i put a load on it (12v 21 watt) it is dropping to 10,8v. i'm not sure if this is normal or not. The 12v line is rated for 2.5A. Ac on the 12v line is 80 mV. i checked all caps and changed some to be sure

[anno]

Re: lg 26LC2R lcd tv backlight turns off

hmm now tv is turning on again (with 2 sec to black error), strange.
I used oscilloscope and put probe on top of both inverter transformers. The probe picks up the oscillation of the transformers. Both transformers oscillate. So i think there is a bad lamp in panel

[anno]

Re: lg 26LC2R lcd tv backlight turns off

Ok i found out i can test the EEFL lamps wit a CCFL tester of ebay

i tested all lamps. you can test each lamp seperatly or all lamps together. all lamps light up. so the backlight eefl lamps are fine.
or maybe inverter is going into protection because of age of lamps, maybe using more current

[tom66]

Re: lg 26LC2R lcd tv backlight turns off

Inverters don't sense lamps which are ageing, unless they've stopped working entirely. That looks like a neat gadget, might have to consider one of them myself.

[anno]

Re: lg 26LC2R lcd tv backlight turns off

ok i see. Yes it's nice and cheap gadget. works ok.

does anyone know what is the primary and secundary of the inverter transformers?