LG 42LB1DR No Video or Sound

[IRShifty]

Re: LG 42LB1DR No Video or Sound

Measurements on the 3037 chip:
Fb - 0.67
Vcc - 4.11
LDrv - "-0.02"
Gnd - "-0.02"

SS/SD - 0.05
Comp - 0.03
Vc - 3.56
HDrv - 0.02

Refer to the attachment diagram for the PIN layout.

I also was able to check the voltage in the area you specified earlier. I attached the image again for reference. The area read 5v.

[tom66]

Re: LG 42LB1DR No Video or Sound

Vcc is a bit low - should be 4.0 - 4.4V minimum - this could be the problem.

The feedback voltage is also too low - should measure 1.25V. The feedback is the signal going to the controller IC to tell it if the output voltage is in regulation.

The fact that both HDrv and LDrv appear low does seem to suggest a problem - however your multimeter may be averaging the pulses these pins should provide.

I would say replace the controller IC and maybe the two MOSFETs but I'm not entirely sure right now.

[tom66]

Re: LG 42LB1DR No Video or Sound

Just noticed: SS / SD

This pin provides soft-start for the switching regulator. An internal current source charges
an external capacitor that is connected from this pin to ground which ramps up the output
of the switching regulator, preventing it from overshooting as well as limiting the input
current. The converter can be shutdown by pulling this pin below 0.5V.

As the voltage is below 0.5V this could be your problem. It's definitely not going to help.

[IRShifty]

Re: LG 42LB1DR No Video or Sound

Okay well lets do it and see. Which MOSFET's do you suggest replacing? U202?

[tom66]

Re: LG 42LB1DR No Video or Sound

Okay well lets do it and see. Which MOSFET's do you suggest replacing? U202?

U202 as well as the two MOSFETs - the 8 pin devices that look similar to U202.

[IRShifty]

Re: LG 42LB1DR No Video or Sound

I actually meant D202, and which MOSFETs are 8 pin? I'm not seeing them. Thanks

[tom66]

Re: LG 42LB1DR No Video or Sound

These devices

[IRShifty]

Re: LG 42LB1DR No Video or Sound

Okay cool. I'm having a hard time finding those MOSFETs, they read 4410n over AA60B. Closest I can find is http://www.ebay.com/itm/5PCs-AO4410-...item3370b287da Can you let me know if you think this part will work or if you can locate a better location to purchase them. Thanks

[tom66]

Re: LG 42LB1DR No Video or Sound

I think eBay is going to be your best shot for these devices, but I'm not certain the MOSFETs are at fault. The 3.4V is definitely your problem. I'm suspecting the controller IC more, so try and replace that too (possibly if you can get that cheaper, try it first.)

[IRShifty]

Re: LG 42LB1DR No Video or Sound

Received the IC today from Digikey. Install went good. Same no display issue, still has a delay on turning off/on. Took some measurements on the 3.4v lines and they are all now showing 2.2v. Where to now? Thanks

[tom66]

Re: LG 42LB1DR No Video or Sound

Hmm. This is strange, very strange. Did you replace the MOSFETs at the same time, too?

In some situations I've found it easier to use something like one of these:

http://www.ebay.co.uk/itm/DC-to-DC-B...#ht_1751wt_956

instead of trying to track down the fault which can be challenging without an oscilloscope to check waveforms.

You'll have to wire it into the 12V or 19V supply.

[IRShifty]

Re: LG 42LB1DR No Video or Sound

I did not replace the MOSFETs. Do you recommend purchasing a board like that before replacing the MOSFETs?

[tom66]

Re: LG 42LB1DR No Video or Sound

I did not replace the MOSFETs. Do you recommend purchasing a board like that before replacing the MOSFETs?

If you can replace the MOSFETs at a reasonable price - sure, go ahead. There is a remote possibility they could cause the problem.

If not use the DC-DC board I've linked you. What does the board say about 3.4V output current (e.g. 1.5A?) The DC-DC claims 3A, but I'm sceptical that diode can do that.

[alikhasan1]

Re: LG 42LB1DR No Video or Sound

Hi Guys . Somebody help me with the power supply schematics diagram . LG 42LB1DR .its been two months when i get this TV . Please help where or how to find the schematics diagram for LG 42LNB1DR . THANKS to you . Best Regards .

[IRShifty]

Re: LG 42LB1DR No Video or Sound

Hey so I just got the TV working. I purchased 2 MOSFETS to replace the 8pin ones on in the specified area. Replacing these MOSFETS was a pain because even after i melted the solder with my heat gun the MOSFETS would not come off easy because they were held on with some type of adhesive as well. I was able to replace one and while replacing the other i became extremely frustrated and a handful of the CAPS i replaced started falling out do to the lower rosin-core solder becoming fluid. I stopped and did not replace the other MOSFET or the CAPS that fell out. I found a replacement power board listed in working condition on EBAY and was able to buy at my offer of $25 with free shipping. I installed the new board and the TV is now working great. Thank you for all your help and I will still becoming back here first when I have issues. Thanks guys!

[arman960]

Re: LG 42LB1DR No Video or Sound

Hello,

TOM66, I am working on 42" LG LCD TV. It seems like I can see the video with flash light , but otherwise the screen is black blank. So probably the inverter board is not kicking in.

I checked the output from the power board , all the output looks like giving required voltage but, 3.4V on giving only 1.9V

please let me know how I can connect this output voltage. What component may be bad on it? why am I not getting 3.4V?

I appreciate if you can give me any suggestion.

[arman960]

Re: LG 42LB1DR No Video or Sound

I checked all the voltage on each pin. All of them ok. But accept one , 3.4V ON is giving only 1.9V

How do I get it to give output 3.4v. Probably that is why it's not turning the inverter board.

Do I look for bad caps on power board. Or some other components?

[arman960]

Re: LG 42LB1DR No Video or Sound

exposed screw hole? You meant ground? Sorry I could not understand what you meant by exposed screw hole.

do you think this low 1.9v is stopping the inverter from turning on? Or my inverter is bad?

I am getting 24V into inverter board.

[arman960]

Re: LG 42LB1DR No Video or Sound

I used to get good picture on this tv. Only problem was half of the screen used to stay dark for half an hour when, after warm-up whole screen was full bright.

Suddenly the inverter stopped working. I can only see the lcd working with a flash light.

Since you have experience solving this kind of issue, I would like to know is this my bad inverter or bad power board?

[retiredcaps]

Re: LG 42LB1DR No Video or Sound

TOM66, I am working on 42" LG LCD TV.

@arman960.

Do not continue posting in this thread. Continue your post at

https://www.badcaps.net/forum/showthread.php?p=266365

Cross posting in multiple threads is heavily frowned upon by regulars here (especially me). It creates confusion and causes way more work than necessary for us. Pick one thread and stick with it.