LG 26" LCD won't turn on


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LG 26" LCD won't turn on

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skor78
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Dec 2, 2011, 11:37 PM

Post #1 of 13 (16409 views)
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LG 26" LCD won't turn on	Can't Post

Hi,

I have a LCD TV from LG, model 26LX1R, that won't turn on. It as the red light indicating power, but it won't respond to either power button on TV or remote.

Additional info:
- Symptoms started happening by not responding to power button in the morning, after turning on power cord, from 5min up to 1h until it worked..
- The TV was connected to a protective power cord, that was switched off at night and on in the morning.
- TV was tested plugged into the wall, with a different power cord and in a different house (to test electrical distribution).

I have some experience in repairing laptops, mobiles and other small gadgets, but i must admit i have no experience in TV. I'd send it to a tech, but i'm unemployed and it seems to be bad luck one after another..
If you guys could give me some pointers in how can i diagnose and fix the problem i'd be deeply appreciated. I know it's not much but i have a good multimeter to help in diagnose.

Thanks in advance! Cheers!

skor78
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Dec 11, 2011, 12:23 AM

Post #2 of 13 (16374 views)
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Re: [skor78] LG 26" LCD won't turn on [In reply to]	Can't Post

Hi,

I've opened the TV even before i posted here, capacitors seem fine, but without an ESR available it's difficult to be sure. I forced the tv on by shorting pwr connector with 5v (in standby i can only read the 5V, others (3.3V,6V,12V,24V) are off), i ear the switch "tlac", backlight and voltages come on, and seems fine, but it's hard to check everything because i have one hand occupied on the short and the tv on a precarious position..

It seems to me that the board/IC that is supposed to provide continuous 5V through the pwr connector is not doing its job.

But right now it's all still very blurry to me, i'm gonna do some more tests and post results.
If you have any more suggestions they would be deeply appreciated!!

skor78
New User

Dec 12, 2011, 1:41 AM

Post #3 of 13 (16351 views)
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Re: [skor78] LG 26" LCD won't turn on [In reply to]	Can't Post

Hi,

New info. When i shunt 5VSB and PWR ON/OFF, tv works fine, even ON/OFF button on the dash works fine. Problem is, when it's shunted, and i plug it to the wall, the tv automatically turns on. I fear this can damage the tv with a power peak. Any suggestions? For the so called best TV repair help forum on the internet, this is being fairly disappointing..

Thanks!

mel
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Dec 12, 2011, 3:01 AM

Post #4 of 13 (16347 views)
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Re: [skor78] LG 26" LCD won't turn on [In reply to]	Can't Post

The manual that I have says check crystal X800

skor78
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Dec 12, 2011, 3:22 AM

Post #5 of 13 (16346 views)
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Re: [mel] LG 26" LCD won't turn on [In reply to]	Can't Post

I've checked the service manual, and X800 runs at ~19MHz, no way i can check this with only a multimeter. My multimeter has frequency meter only up to 200KHz. Any ideas in how to test this without osciloscope?

Thanks!

(This post was edited by skor78 on Dec 12, 2011, 3:29 AM)

mel
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Dec 12, 2011, 4:41 AM

Post #6 of 13 (16339 views)
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Re: [skor78] LG 26" LCD won't turn on [In reply to]	Can't Post

I'm not sure what you mean by "I forced the TV on by shorting pwr conector with 5V". Where did the 5V come from?

jerseysoutlet
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Dec 12, 2011, 8:49 AM

Post #7 of 13 (16336 views)
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Re: [skor78] LG 26" LCD won't turn on [In reply to]	Can't Post

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(This post was edited by jerseysoutlet on Dec 12, 2011, 8:50 AM)

skor78
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Dec 12, 2011, 10:37 AM

Post #8 of 13 (16333 views)
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Re: [mel] LG 26" LCD won't turn on [In reply to]	Can't Post

Quote

I'm not sure what you mean by "I forced the TV on by shorting pwr conector with 5V". Where did the 5V come from?

I think that "..shunt 5VSB and PWR ON/OFF" in the connector answers that question. which seem to be the same in troubleshooting. I decided to skip the X800, check IC806 in next step, if everything else is fine, i think it's safe to assume X800 need reclacing. what do you think?? regards 

(This post was edited by skor78 on Dec 12, 2011, 11:23 AM)

mel
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Dec 12, 2011, 11:33 PM

Post #9 of 13 (16318 views)
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Re: [skor78] LG 26" LCD won't turn on [In reply to]	Can't Post

That is what I was going to suggest, but I would also suspect C801 and C802 as well as IC806

skor78
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Dec 14, 2011, 10:32 PM

Post #10 of 13 (16303 views)
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Re: [mel] LG 26" LCD won't turn on [In reply to]	Can't Post

Hi,

I've been crazy busy last couple of days, but today i tested IC806, 5V are there and everything seems fine. C801 and C802 are not present onboard (factory empty slots). But still could't find Q1001, both, on the boards, and in the schematics in the service manual (pdf, may due to my small screen)..
If you could help me locating it, i'd appreciate.

Following the troubleshooting, everything points to Q1001 faulty part. Can you also help me in where can i buy this part?

Thanks.

mel
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Dec 15, 2011, 12:10 AM

Post #11 of 13 (16296 views)
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Re: [skor78] LG 26" LCD won't turn on [In reply to]	Can't Post

Q1001 is a 2SC3875S and is just off of pin 10 of CN804. I don't have a placement chart so I can't tell exactly where it is physically located on the board (check for a surface mount xistor on the back of the board). It crosses to an NTE2408 which should be available from most online electronics parts suppliers.

(This post was edited by mel on Dec 15, 2011, 12:39 AM)

skor78
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Dec 15, 2011, 1:31 AM

Post #12 of 13 (16290 views)
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Re: [mel] LG 26" LCD won't turn on [In reply to]	Can't Post

Found it! Thanks Mel! But I'm confused..
Will i be able to test Q1001 with the mainboard connected only to the power board and all other cables disconnected? should i connect the cable that comes from the front buttons or any other?

Also, i noticed contacts on Q1001 are a little oxidated, maybe try a quick reflow can do the trick? Give me your thoughts.

Thanks again.

mel
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Dec 15, 2011, 3:42 AM

Post #13 of 13 (16287 views)
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Re: [skor78] LG 26" LCD won't turn on [In reply to]	Can't Post

First check C1297. Since it and ZD1400 are in parallel with C to E of Q1001 it cannot be checked in circuit. Are the solder joints just oxidized or are they grainy? Touching them up wouldn't hurt but oxidation can be cleaned off with denatured alcohol..

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