LG 60lb5200 LCD TV - No Power - No Standby Light

[Landon6544]

Hi. Just bought a repair project. LG 60lb5200 has no standby light. I've tested the pin voltages on the power supply and get nothing on any of them. The symbol on the bottom pin reads 'EN'. I assume this is the standby voltage out? I've searched other posts, but can't find this abbreviation mentioned. I tested the main transformer outputs and got nothing. The fuse is good and reads normal AC voltage across it. Can someone lead me in the right direction with narrowing down the problem component? I'd rather not have to pay $100 for a new board.

I've included pics.
Thank you!

[PotShotScott]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

I don't have any experience with this particular TV but some of my Navy Avionics course training is coming back to me (it's been 26 years since A school). I'd be looking closely at the diodes that feed into the transformer. They might be part of a rectifier circuit that drives the transformer that feeds into the DC/cold portion of the board. Maybe one or more of them died and they just "look" okay?

[freakaftr8]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

Can you check the main primary side capacitors? Negative lead black positive lead red to each side of the capacitor while it's plugged in on DC voltage you should be reading about a 170 V DC.

Location C9 or C10

[CapLeaker]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

Check D3 and D9 for a short on the secondary. One of them is for 12V, the other for the 24V rail. What is written on U1?

[Landon6544]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

Ok, I checked D3 and D9. Those are the three terminal voltage regulators on the DC side, right? I'm getting 0 volts.

Also, I noticed when I move the board that I hear something rattling in one of the components. Sounds like little pieces of loose glass or metal. Could that be from the transformer?

[Landon6544]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

C9 and C10 both read 167v DC.

[Landon6544]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

A bit more... D3 and D9. Are those MOSFET transistors? I'm learning a lot already. Haha. I'm pretty sure the noise is coming from the varistor, or brown box down near the fuse. Is that supposed to have loose pieces inside?

I also tested the bridge rectifier on the hot side. Getting 167v DC across the positive and negative terminals, and around 120v AC on both of the middle inputs.

[Andrew F. Ali]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

D3 and D9 are the subscripts for Diodes.

[Landon6544]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

Well, I initially assumed that D stood for "diode", but the component has three terminals, although there's also an 'M' designation there. I can't read the part number because of the heat sink. I only learned basic electronics, and that was in Air Force tech school back in 2002. So... I'm learning and refreshing. The heat sink on the hot section is attached to similar looking components, but they have a Q. I'm guessing those are transistors.

[budm]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

This is an always on power supply to supply 12V and the 24V, it also has PFC Voltage booster.
What is the resistance reading of R33?
Can we see the whole backside of the TV showing all the boards and how they are connected together?
More likely the AC feeding this board is done through a switch.

[Landon6544]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

Oh wow... I just noticed that the board is burnt underneath that resistor. The ohm reading is 11, 700 Ohms. I can't tell what colors the stripes are, though.

[budm]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

What is the P/N of the 16-pin SMD IC U1 in that section of the circuit?

[budm]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

http://www.shopjimmy.com/catalogsear...?q=LG+60lb5200
LG COV32809701 Power Supply
http://www.shopjimmy.com/lg-cov32809...wer-supply.htm

R33 looks to be 10K resistor based on the pictures from shopjimmy.
Pictures provided by shopjimmy.

[Landon6544]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

Ha, it looks nothing like those colors on my board, but it's reading 10.6k. So, even though it looks burnt, it seems to be reading within tolerance? And... I don't see any IC chips on the power board. Do you mean on another board?

[budm]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

Ha, it looks nothing like those colors on my board, but it's reading 10.6k. So, even though it looks burnt, it seems to be reading within tolerance? And... I don't see any IC chips on the power board. Do you mean on another board?

The IC U1 is right on the bottom side of that power supply board. I hope you do have the tools and know how to do SMD repair.
10.6K is good enough, but something is drawing too much current through that resistor.

[Landon6544]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

Man... I'm really having trouble reading it. Might need to find a magnifying glass. If I can determine that it IS the IC causing the issue, I might be able to get it fixed. I don't have the tools for soldering something that small.

[budm]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

Without the IC P/N to get the specification sheet of the IC, then there is no way to find out if the IC is getting the VCC to run or not, and that 10K resistor looks to be connected to one of the IC's leg.

[Landon6544]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

Ok, this is actually the same model that another member is having issues with, and you asked him the same question. He's getting voltages on his pins, however. They're just too low.

Anyway, the printing is clearer on his IC chip. I've included the manual for it.

[Landon6544]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

What do I need to test to isolate the IC chip as the culprit?

[budm]

Re: LG 60lb5200 LCD TV - No Power - No Standby Light

What do I need to test to isolate the IC chip as the culprit?

See my post #17 about the VCC.