LG 42LV3500 trips circuit breaker

[tibimakai]

I have picked up this LED TV and when I plugged it in, it tripped the circuit breaker right away.
Today, I have removed the power supply board and tested the rectifier, all heatsink mounted transistors and dioded on the primary side.
I haven't found anything open or shorted.
There are a couple of fuses, they are OK as well.
I'm tempted to plug it in again, but before I would try again, I'm looking for ideas on what else should I check?
I didn't have time to take pictures, but shopjimmy has some nice pictures for now.

[freakaftr8]

Re: LG 42LV3500 trips circuit breaker

Tripped your house breaker? Stupid question but did you check the cord for damage? Next ohm across the main capacitor for a short.

[tibimakai]

Re: LG 42LV3500 trips circuit breaker

Yes, the house breaker.
I have checked the cord and I couldn't find a short. It was some kind of tape on the cord inside the TV.
That is the problem, I can't find anything shorted. I guess, I will plug it back in again, after I inspect closely that cord.
Thanks, I will let you know of the outcome.

[budm]

Re: LG 42LV3500 trips circuit breaker

Use the series lamp that you built.

[tibimakai]

Re: LG 42LV3500 trips circuit breaker

I'm thinking about that, I'm just not sure if that bulb it's big enough for this TV.
I may solder in another power cable. It's my #1 suspect now. I have measured the cord for short and I din't see any problem there, but maybe if I bend the cable it's a different story.

[budm]

Re: LG 42LV3500 trips circuit breaker

If you have short that can trip the house breaker, then the lamp (100W) will be fully lit. You can just power up the power supply board by itself. It is LED backlights so it does not draw that much power.
Did some one work on this TV before? Since the main fuse (5A) did not blow and it is the first thing the Line cord is connected to, then it has to be some that short BEFORE the fuse, you cannot blow the 15A house breaker without blowing the 5A fuse first.

[tibimakai]

Re: LG 42LV3500 trips circuit breaker

It seems like somebody worked on it, because the screws for the boards were all wrong lengths.
The guy, it was a cell phone repairer, so I guess he pocked around in the TV.
He sold it to me, without base and remote for $40. I hope the screen it's fine.
I had to pick it up in the dark, I had to park in the red zone.
Same story with a Sharp LC42SB45U, I have picked it up the same night. Only green light is on, no backlight at all. Did not have a chance to open that one up. I had one of these in the past.

[tibimakai]

Re: LG 42LV3500 trips circuit breaker

The black wire had a small exposed area. I guess that touched the chassy.
After taking care of the cord, I have plugged it in and the TV seems completely dead.
There is a relay, which in my opinion it should click when the TV is plugged in, am I right? It doesn't click.
The rectifier doesn't have any voltage at +/-. No voltage at the main capacitors either.
I have the SM, but I don't see the power supply in there. There are some separate small schematics, for each low voltage power supply, like 3.3V, 1.26V, etc..
It seems like, LG doesn't give out the power supply schematics for these TVs. I have found other schematics in different size TVs from the same family and it's the same.

[tom66]

Re: LG 42LV3500 trips circuit breaker

fuse good? Relay on most of these sets will only click in after the TV exits standby mode, I had LG 37LE4500 with similar PSU and it only clicked when leaving standby.
LG rarely give out PSU schematics as they consider PSUs nonserviceable items. Replace only. I disagree but what can you do.

[tibimakai]

Re: LG 42LV3500 trips circuit breaker

All the fuses are OK.
There is a transformer at the middle of the board, has a metal cover(T101), and above it there is a fuse with two orange stripes on it. That fuse shows 167V.
At the main rectifier should I have voltage before the relay kicks in, or only after?
Not sure here, what should I measure?

[freakaftr8]

Re: LG 42LV3500 trips circuit breaker

Are you getting 5v standby?

[budm]

Re: LG 42LV3500 trips circuit breaker

Looking at the pictures, the relay must be on for the Bridge rectifier to get the Line voltage to the two middle pin of the bridge, but right now the standby power supply should be running (generated by transformer T501).
If you check the AC voltage, one probe on the 'N' of the incoming AC input connector, the other probe on the Anode of D501, you should have 120VAC.

[tibimakai]

Re: LG 42LV3500 trips circuit breaker

Didn't have much time today. Removed all the Christmas stuff.
Tomorrow, I will check that D501 and the standby voltage.

[tibimakai]

Re: LG 42LV3500 trips circuit breaker

I haven't measured properly the D501. I have used the minus of the main caps. I'm getting 55V this way. I will have to measure it again.
The standby voltage, should go through the two diodes next to the T501 transformer, right? They are D201 and D202. At those diodes I'm getting only 0.43V.
It seems, that the standby voltage should be 3.5V.

[tom66]

Re: LG 42LV3500 trips circuit breaker

Measure both ends of the diodes. Also, try to hear if there is a faint ticking coming from that transformer. And try measuring voltage without main board installed as well.

[budm]

Re: LG 42LV3500 trips circuit breaker

"I haven't measured properly the D501" The test I want you to do is for testing the AC HOT and Neutral to see if it gets all the way to the diode that supplies voltage to the standby power supply section. You must test it as I have instructed in post 12.
"Looking at the pictures, the relay must be on for the Bridge rectifier to get the Line voltage to the two middle pin of the bridge, but right now the standby power supply should be running (generated by transformer T501).
If you check the AC voltage, one probe on the 'N' of the incoming AC input connector, the other probe on the Anode of D501, you should have 120VAC."
If the AC feeding the standby power supply is OK, then you should have 170VDC on the TWO LEGS OF C501, C502 which are the main filter caps for the standby power supply.

[tibimakai]

Re: LG 42LV3500 trips circuit breaker

Actually, I remember measuring those two caps and there is 167V.

[budm]

Re: LG 42LV3500 trips circuit breaker

OK, so now can concentrate in that standby power section to see whay it is not putting out the standby voltage. P/N of that SMPS 8-PIN IC?

[selldoor]

Re: LG 42LV3500 trips circuit breaker

Damn - done it again - just spent 10-20 minutes looking at the pictures trying to spot
a problem area then discover they are not the boards!! Should be a law against it except for exceptional circumstances. Think I will have to enter it into the thins that p me off thread

[tibimakai]

Re: LG 42LV3500 trips circuit breaker

Sorry about that selldoor. I have also mentioned in that post, that the pictures are from shopjimmy.
I didn't have time to take pictures and I don't have room either to take pictures.
This TV is placed on my computer chair(in the garage) in an angle and that is how I work on it. On my workbench I have the 52" Sony, on my other work table I'm working on a 40" Samsung and a Yamaha receiver.
I thought, that this TV it will be a simple fix.