My lg tv has sound but no picture

SOURCE: 42 inch LG Plasma TV - Lost picture

ysus pcb that supplies voltage to the panel is faulty

SOURCE: LG 42LG5 TURN ON TV PICTURE GOES BLACK

This could be 1 of a few things here. Without opening up your set and trying to look at voltages or indiciator lights I couldn't tell you exactly without some more info.

Without looking at it myself here are my thoughts and where I would first look at.

It may be a main board because:
1) Main board processes all your audio/video signals. Bad main board means bad video processing. Could do that. Especially if the main board is not sending the right signal or a bad signal to the rest of the boards so they don't do their jobs. 

It may be a power supply because:
1) Power supply is well, the power supply. If it's sending inadaquete voltage to the main board you may not be recieving enough juice to keep that main board doing your video processing or further up the line keeping enough juice flowing to your TCon board to keep it telling things where to go and what to do. The power supply sends voltages to your Ballast board(controls your lights) and to your main board through which power is supplied to your TCon board via a LVDS line and a +12/+16V signals. If the power supply isn't pumping out enough juice to keep the TCon or Main Board running, it could be a problem. By the same token it could be that your P/S isn't sending power out to your ballast board. 

It could be a TCon because:
1) If the TCon is bad, you won't get your pictures. This could be the TCon board itself or the LVDS cable from your TCon to your Main. However, with few exceptions, if it's a bad TCon you're looking at a total panel replacement. 

It could be a ballast board because:
1) The Ballast Board controls the lighting behind the LCD screen. If this isn't working right you won't be seeing much of anything without that back lighting. If this is bad, it's a panel replacement. These are not field replaceable items by LG. 

Based on the symptoms, without more data or a eyes-on view of it, I would say you're most likely looking at a Main Brd or PSU problem. 

SOURCE: I have a LG 42LB1DR

I purchased four 2200uf @ 25v capacitor’s for $8 at a repair shop. I upgraded to 25v because these will run cooler. The tv came with 2200uf @ 10v Samxon caps that seem to be problematic in all the units they were used in. Do not buy Samxon if you do this job yourself.... I opened the set by taking off the plastic back panel and then by removing the second metal panel. There are three boards and a hard drive. The board on the far left just above where the plug goes in is the power supply board. There are five data cables and one red power cable attached to it that can be removed simply by unplugging them. The board is fastened to the unit with five small screws, one on each corner and one in the middle of the right side. If you look for three green capacitors grouped together around the middle of the board and slightly off to the right, you will probably see one that is bulging out at the top. This is most likely "C235", the main problem. The other three caps that need replacing are C202, C201 and C219. C219 is closer to the top part of the board.....
The process to replace is simple, believe it or not, and it could save you hundreds of dollars. 1, Go to RadioShack and buy a cheap soldering iron and a small roll of solder. 2, Buy four, 2200uf @ 25v capacitors, online or at an electronics store. 3, Plug the soldering iron in and let it heat up. 4, Locate C235 on the back side of the board and mark the negative terminal with a felt tip marker (you want to make sure that you put the negative terminal on the capacitor through the right hole, otherwise you will pop the cap. The negative terminal is clearly marker on all the capacitors). 5, With needle nose pliers, grip the cap and pull down while heating up the terminals. The cap will eventually come out. 6, Put the new cap in (you may need to heat the solder that is left on the board to clear the hole so it can push through). 6, When both terminals are through, bend them slightly so it stays in place. Take the solder and stretch out a few inches off the roll and while holding it in one hand, lightly touch the base of the terminal where it comes through the board, with the soldering iron and the solder at the same time. --- Try not to use too much solder.. you only need a tiny drop. This will solder the cap in place. 7, cut off the terminals close to the board with some snips and repeat this on the other three. 8, put the board back in, plug in the cables. Test the TV before putting the back panels on. It should work fine if all went well..... If you hear a pop than you reversed the terminals on a capacitor and that one will need to be redone correctly.... This might sound lengthy and potentially difficult but its worth a try. Otherwise you can pay someone to replace the entire board for BIG BUCKS with the same junk caps on it and have the same problem in a year or so. LG doesn’t want to take responsibility for this and I'm sure that it has cost a lot of people a lot of money for about $8 in parts........... This worked for me and it can work for anybody with the same problem.. Good Luck!

SOURCE: LG 42 LCD no sound or picture

This is probably bad capacitors on the power supply board. My LG 42LB1DR has a known problem with this and I replaced the four bac capacitors myself and saved 5-6 hundered dollars that I was also told that it would cost to fix. I fixed for under 10 dollars and about 20 minutes. LG knows about it but they dont really want to admit it. My TV was only 26 months old when this happened. The four capacitors are made by Samxon and are 2200uf @ 10v. They are junk so even if you have the entire board replaced for say $200 its just going to happen again. They need to be replaced with a different brand.

SOURCE: LG 50PX4DR plasma tv

I had the same exact problem as posted above. My 50" LG plasma was out of warranty for 1 year! I called the LG executive call center, and they were very helpful. They offered to pay for the parts and labor. They recommended a few local repair shops, and they set everything up for me. The tech came out within 4 days with one part. The tech had to come out one more time the following week, since more parts were needed for the repair. The Y sustain board, along with 2 adjacent parts that are required to be replaced as a set, and the power supply had to be replaced (parts alone cost just over $900). TV is like new again; I'm very happy with how LG handled it, and made what could have been a bad experience a good one.