32LG2000 wouldn't turn on

[Kaar3l]

I have a 32LG2000 that turns on sometimes and sometimes doesn't. It was maybe 1 time out of 10 about a week ago. (tv was warm) Now I turned it on and it has been 5/5 acting nicely. I think it might turn on better when it is cold, but when it gets warm, it has problems.

I have changed a lot of caps, but the problem is still there. On picture I marked the caps with red dot that are new. I also changed caps inside inverter.

When the tv did that: Blinked 3 times, then the light turns green and it should be on. I measured then voltages from power supply and there was no 16,5V, but when it was working fine, then there was 16,5V on that line.

[CapLeaker]

Re: 32LG2000 wouldn't turn on

check the feedback circuit of the 16.5V rail. Maybe the optocoupler is going bad.

[Kaar3l]

Re: 32LG2000 wouldn't turn on

check the feedback circuit of the 16.5V rail. Maybe the optocoupler is going bad.

Could you give me some more hints, I haven't checked that before?

[Kaar3l]

Re: 32LG2000 wouldn't turn on

check the feedback circuit of the 16.5V rail. Maybe the optocoupler is going bad.

Changed optocouplers and didn't change the problem.

[nomoresonys]

Re: 32LG2000 wouldn't turn on

just had similar problem with sony, didnt want to turn on after turn off, and only would turn on about 1out of 5 times, no matter how long it was, turned out to be bad mainboard.

[budm]

Re: 32LG2000 wouldn't turn on

The 16.5V power supply is generated by the same transformer (large transformer T101) and circuit that also generated the 24VDC for the inverter.
So do you know if the 24V also disappears? If it does then we need to check the 16.5V/24V power supply section.
http://www.shopjimmy.com/lg-eay40504...pply-unit.htm#

[Kaar3l]

Re: 32LG2000 wouldn't turn on

The 16.5V power supply is generated by the same transformer (large transformer T101) and circuit that also generated the 24VDC for the inverter.
So do you know if the 24V also disappears? If it does then we need to check the 16.5V/24V power supply section.
http://www.shopjimmy.com/lg-eay40504...pply-unit.htm#

Just tested and from 24V line comes about 0,3V, so 24V is gone also.


I noticed weird thing when measuring the voltages, if I bent slightly the board, then a quiet buzz noise was coming out of that transformer.

[CapLeaker]

Re: 32LG2000 wouldn't turn on

What happens if you disconnect the backlight an turn it on?

[nomoresonys]

Re: 32LG2000 wouldn't turn on

Just tested and from 24V line comes about 0,3V, so 24V is gone also.


I noticed weird thing when measuring the voltages, if I bent slightly the board, then a quiet buzz noise was coming out of that transformer.

ok, no 24v, thats different than the issue I had, where there was 24v.

[budm]

Re: 32LG2000 wouldn't turn on

Just tested and from 24V line comes about 0,3V, so 24V is gone also.


I noticed weird thing when measuring the voltages, if I bent slightly the board, then a quiet buzz noise was coming out of that transformer.

OK, that is what I expect it not to have 24V either.
At this point inspect the solder joints on the board real well, I will have to look at the bottom side of the board to see how the transformer for the 16V/24V are driven.
As the other has suggested, if the inverter is drawing too much power it will cause the circuit to shutdown due to over current draw.

[Kaar3l]

Re: 32LG2000 wouldn't turn on

OK, that is what I expect it not to have 24V either.
At this point inspect the solder joints on the board real well, I will have to look at the bottom side of the board to see how the transformer for the 16V/24V are driven.
As the other has suggested, if the inverter is drawing too much power it will cause the circuit to shutdown due to over current draw.

I tried unplugging inverter and then powering it on, and results seemed the same. I tried watching picture with flashlight, but didn't see anything.

But couldn't be a problem on the other side of power supply some small smd chip(NCP1396AG)?

[vinceroger69]

Re: 32LG2000 wouldn't turn on

As budms post 10 in sure if you can post good clear pictures of the bottom of the board he may have some more tests you can perform.

[CapLeaker]

Re: 32LG2000 wouldn't turn on

I tried unplugging inverter and then powering it on, and results seemed the same. I tried watching picture with flashlight, but didn't see anything.

But couldn't be a problem on the other side of power supply some small smd chip(NCP1396AG)?

Did the 24V and the 16.5V come up though?

[Kaar3l]

Re: 32LG2000 wouldn't turn on

Did the 24V and the 16.5V come up though?

Just tested that, only 5V is present. 24V and 16,5V are missing.

I did a picture under light, hope it is ok.

[budm]

Re: 32LG2000 wouldn't turn on

The picture has to be straight shot, I cannot trace the connection form that picture.
We need to look in that 16v/24v SMPS section.
You can take straight pictures of the whole board and then in 1/4 sections which will make it much easier for me to trace out the circuits.
For example of sectional shots:
http://s807.photobucket.com/user/bud...?sort=3&page=1

[Kaar3l]

Re: 32LG2000 wouldn't turn on

I did bigger pics:
http://s254.photobucket.com/user/Kaa...?sort=3&page=1

[Kaar3l]

Re: 32LG2000 wouldn't turn on

I changed the NCP1396AG, nothing changed.

[CapLeaker]

Re: 32LG2000 wouldn't turn on

So you changed the little PWM chip on the backside, no change. Check C114 and C117. I hope you checked the rectifier diodes on the 24 / 16 V output rail for shorts.

[vinceroger69]

Re: 32LG2000 wouldn't turn on

I see you have changed most capacitors on the psu but you have left 4 small ones unchanged i would also change these to rule them out too.

[nomoresonys]

Re: 32LG2000 wouldn't turn on

just had similar problem with sony, didnt want to turn on after turn off, and only would turn on about 1out of 5 times, no matter how long it was, turned out to be bad mainboard.

I think I was wrong about this, now I'm thinking it's a bad cap on the power supply, even tho all the voltages are correct, not sure.