LG 32LC2R-CJ No Backlight

[s_henya]

Hey friends,

I need your help on this one,

The TV powers on, but got no backlight and had strong hissing noise.

Replaced almost all of the caps on the PSU.
Hissing noise stopped :-), but still got no backlight.

TV remote is working, i didn't check for sound but im pretty sure it's working.

Checked Inverterboard, the white rubber spacers melted down, all the inverted was full of with goo (front and back!).

Tried my best to clean it with alcohol, tested the 8 220uf caps, all were good (capacitance and ESR), all smd fuses were good.

Plugged in and tested it in the dark:

As soon as it powers on i can see that i have backlight for a sec then powers off again.

I tested voltages and i can see 25vdc going from the psu to the inverter.

I think it goes to protection mode as bulbs or transforms are bad... or maybe i have another fault with the psu...

[budm]

Re: LG 32LC2R-CJ No Backlight

The resistance testing on the secondary side of the inverter transformers are good?

[s_henya]

Re: LG 32LC2R-CJ No Backlight

Hi budm,

I wanted to test the transformers, but i dont have a lopt ring tester.

some resistance testing refrence would be much appriciated!

[selldoor]

Re: LG 32LC2R-CJ No Backlight

What are the part numbers on the gray oblong transformers on the inverter board

[s_henya]

Re: LG 32LC2R-CJ No Backlight

i will report the numbers and add a better picture
as soon as i get home...

[s_henya]

Re: LG 32LC2R-CJ No Backlight

As requested another picture of the inverter, it's model and
the transformer: 4004L644 300(GP)

i never checked for transformer resistance, so guidance would be nice,
identifying the primary and secondary winidings...

normal resistance for each coil, and testing it in or out the circuit.

[vinceroger69]

Re: LG 32LC2R-CJ No Backlight

this may help you identify pins etc
http://www.lcdparts.net/TransformerD...ProductID=3182

[s_henya]

Re: LG 32LC2R-CJ No Backlight

thank you vince very helpful link!

just to clarify i will test resistance between pins s1-s2 p1-p2..

and so on?

stupid question but should i test in in or out of the circuit?

[vinceroger69]

Re: LG 32LC2R-CJ No Backlight

I test in circuit (tv off) then if i find a bad one remove and test again. I persume yes you test as you as you say above im sure some one will advise if diffrent. Take the readings for now write down each one per transformer see if any read diffrent.

[s_henya]

Re: LG 32LC2R-CJ No Backlight

thank you very much!

i will post the results tomorrow when i get home...

[selldoor]

Re: LG 32LC2R-CJ No Backlight

Ok - NO power to the board set your meter on ohms 2000 and just test
S1 to S2 and S3 to S4 on each transformer the link vince gave shows
what you should get - better list them all.
EDIT
Test them on the board any that look odd we will tell you to remove and test again
off the board

[s_henya]

Re: LG 32LC2R-CJ No Backlight

OK found one bad transformer:
secondary on one side got 70kohms instead of 1.4kohm
primary was fine 0.6ohm

verifyed out of the board too.

so i need to serch for a replacement.

found some on ebay and aliexpress for about 15$ but i hate ordering and wating about a month for parts.

i will search in the local shops although the odds are very low...

i will update as soon as i can get a replacement.

[s_henya]

Re: LG 32LC2R-CJ No Backlight

So...

I replaced the transformer, and got progress! i got a picture.

the problem is, i can hear some noises, and after some very quick tests no more than 5-10 seconds each.

i didn't get a picture everytime.

im afraid that i still have some unresolved issues to deal with the psu/inverter.

any more guidance?

[s_henya]

Re: LG 32LC2R-CJ No Backlight

The hissing is coming out of the inverter or CCFL's

In order to test the bulbs, i ordered this CCFL tester,
http://www.aliexpress.com/snapshot/6515156861.html

As soon as i get it i will update the results..

[vinceroger69]

Re: LG 32LC2R-CJ No Backlight

Did you test the new transformer before you fitted it? ive had a brand new one faulty!

[s_henya]

Re: LG 32LC2R-CJ No Backlight

The transformer seemed as it was taken out of an inverter (used)
i tested the resistance as i did before and it was good.

i really don't know why i still have issues as everything looks good.

that's why i ordered the tester in order to eliminate CCFL faults.

[vinceroger69]

Re: LG 32LC2R-CJ No Backlight

Hissing does sound like a bad ccfl wiring or mounting point its just which one theres a few in these sets if i remember.

[s_henya]

Re: LG 32LC2R-CJ No Backlight

Finally had some time to do some more testing..

Soldeired all the inverter transformers again.

Cleaned some more of the inverter pcb,

Finally found i had a problem with one of the ccfl sockets on the inverter.

Fixed it.

NOW THE TV IS WORKING AGAIN!

[budm]

Re: LG 32LC2R-CJ No Backlight

Thanks for the follow-up.