LG TV Turning on and off constantly (trying to repair this)

[zsemago]

My LG TV (52lg50) turns on and off constantly *only when you first turn it on*.

It will turn on and off for about 2 minutes before it just stays on and acts like a normal TV. The same thing will happen when you turn it off. It will flicker on and off for 2 minutes. So I usually just unplug it from the wall when I turn it off. This has been the status-quo for 3 years.



I finally brought out a TV specialist to take a look. He said the TV looks to be in good shape, and that its likely the mainboard that needs replacing. OK. So I ordered a new mainboard and installed it.

Freshly installed mainboard:

http://imgur.com/gallery/jMJcczI

Moment of truth:

https://www.youtube.com/watch?v=s9TRt8PBWSU

....and its still flickering on and off. So installing a new mainboard didn't do me much good.

Anybody have any ideas as to what could be the issue here and/or how to fix it? I'd really love to figure this out instead of heading over to Best Buy for a new one. The TV works great besides this little glitcharoo.

Thanks!

[ivoh]

Re: LG TV Turning on and off constantly (trying to repair this)

sounds temp related. measure the voltages from the psu while the TV flickers. no sense throwing parts at it until you locate the problem. sounds psu related

[zsemago]

Re: LG TV Turning on and off constantly (trying to repair this)

sounds temp related. measure the voltages from the psu while the TV flickers. no sense throwing parts at it until you locate the problem. sounds psu related

PSU = power supply unit?

[selldoor]

Re: LG TV Turning on and off constantly (trying to repair this)

Yes - or power supply board- post pictures front and back and please use manage attachments so pictures are kept available on this site for reference

[zsemago]

Re: LG TV Turning on and off constantly (trying to repair this)

I found this on the Power Supply board. After a little research these appear to be "MOSFETS" and as you can see there is some brown leaking coming from them. Is this OK?

Pic attached.

[zsemago]

Re: LG TV Turning on and off constantly (trying to repair this)

Power Supply Front & Back Full Pics

[selldoor]

Re: LG TV Turning on and off constantly (trying to repair this)

Mosfets dont/cant leak the brown is probably just flux residue from manufacture
- not a problem.

Do any of the capacitors look swollen or the tops bulged/curved. What make are the BIG capacitors

[Andrew F. Ali]

Re: LG TV Turning on and off constantly (trying to repair this)

Are you able to power ON the TV with the remote control when it is in Standby mode? If you answer NO then the problem is definitely on the Main Board. This could be due to ESD protection component known as a Multi-Layer Varistor (MLV) shorting. It looks like a small SMD diode found on the underside of the Nain Board. Most tomes found inthe 3.3VDD supply. It may carry a Zxx part number. They are actually two back to back zener diodes. check the EEPROM IC SCL and SDA pins that go to ground via the MLVs

[zsemago]

Re: LG TV Turning on and off constantly (trying to repair this)

Mosfets dont/cant leak the brown is probably just flux residue from manufacture
- not a problem.

Do any of the capacitors look swollen or the tops bulged/curved. What make are the BIG capacitors

The big brown capacitors in the photo are by SAMYOUNG.

Nothing looks swollen or bulging. I'm not seeing any residue either besides the small flux leakage mentioned before.

[zsemago]

Re: LG TV Turning on and off constantly (trying to repair this)

Are you able to power ON the TV with the remote control when it is in Standby mode? If you answer NO then the problem is definitely on the Main Board. This could be due to ESD protection component known as a Multi-Layer Varistor (MLV) shorting. It looks like a small SMD diode found on the underside of the Nain Board. Most tomes found inthe 3.3VDD supply. It may carry a Zxx part number. They are actually two back to back zener diodes. check the EEPROM IC SCL and SDA pins that go to ground via the MLVs

**in original post I mentioned I replaced the main board and I'm still getting the same results.

I can't really answer this though as pretty much the only way to turn the TV off is to unplug it. Otherwise it just goes back and forth, turning on and off by itself. Simply plugging the TV in to the wall puts it into the "flicker" mode of on and off.

When turning the TV on it does this for 2 mins then stays on. When turning off it just never goes off. It flickers for a while like its trying to turn off, but usually just stays at "on" after a few minutes of flickering.

I can control it via remote though. The result is as described above.

Sometimes it starts giving me this behavior when I switch from HDMI 1 to HDMI 2, but that hasn't happened lately.

[bammbammfran]

Re: LG TV Turning on and off constantly (trying to repair this)

Since your power supply looks to be ok
I searched your model on ebay and found that they have a few inverters in them and of all the pictures I looked at, 3/4 of them had overheating sections.
so based on that and on the fact that you have flickering associated with the problem, My guess is that one of your inverter boards has a fussy transistor or transformer.

[zsemago]

Re: LG TV Turning on and off constantly (trying to repair this)

I googled this and believe this is my inverter board? http://www.tvpartsguy.com/media/0f/a...6238ec2a_l.JPG

...I took the backs off of all my inverter boards and everything looks good. No bulging, no leaking. Is there something in particular I'm looking for? Could you show me some of the pics you're talking about regarding the "overheating" sections.

Is overheating a factor here? If the TV has been off for 24 hours and has trouble turning on. Once the TV makes it to on all issues are eliminated and the TV will act fine for as long as I need it. The initial turning on and turning it off are the only 2 areas where I have problems.

[bammbammfran]

Re: LG TV Turning on and off constantly (trying to repair this)

here is a good example of over heating where the yellow is tuning orange then brown
If you look at the bottom picture, you will see small black transistors in these areas. these are what parts a cooking

Looks you boards over to see if anything is showing signs of overheating.
Again I am thinking this because you said it flickered
This would normally not affect shutdown of a unit, but ???


http://www.ebay.com/itm/380746797819

[tom66]

Re: LG TV Turning on and off constantly (trying to repair this)

Have you checked those MOSFETs don't have cold solder joints? They look really heated, which could be a sign of a poor or intermittent connection.

It is more than possible you got two boards with the same fault... sellers rarely test their pulled boards despite their claims of doing so.

[bammbammfran]

Re: LG TV Turning on and off constantly (trying to repair this)

Have you checked those MOSFETs don't have cold solder joints? They look really heated, which could be a sign of a poor or intermittent connection.

It is more than possible you got two boards with the same fault... sellers rarely test their pulled boards despite their claims of doing so.

that ebay board is not the OPs board
I posted it just to show them a common issue on these

[tom66]

Re: LG TV Turning on and off constantly (trying to repair this)

I am referring to this photo, the drain leg of the uppermost transistor looks cracked at the board point. Could just be the angle or lighting but might be a sign of a cold joint.
https://www.badcaps.net/forum/attach...0&d=1403290307

[fruitbat04]

Re: LG TV Turning on and off constantly (trying to repair this)

Wouldn't the first step be to see what's happening with the voltages on the power supply when it's turning off and on?

[bammbammfran]

Re: LG TV Turning on and off constantly (trying to repair this)

Hey tom,
YEAH !!
That one rivet looks bigtime messed up !

[zsemago]

Re: LG TV Turning on and off constantly (trying to repair this)

The inverter boards appear fine. I think I have 4 of them? Below is a pic of 1 of the boards. No sign of burnage.

Another pic of the Mosfet thing too.

[zsemago]

Re: LG TV Turning on and off constantly (trying to repair this)

Wouldn't the first step be to see what's happening with the voltages on the power supply when it's turning off and on?

I haven't done this because I don't have the tool to - probably next up to do. I really hope the TV repair guy I paid $90 to check out my TV would've done this cuz it sounds so simple.