LG 50PJ350 Power Supply Repair

[sluhbmet]

Hello All,

I've got a LG 50PJ350 plasma tv that I got cheap because the power supply would click constantly when plugged in, even with no other boards attached to it. After a few evenings of troubleshooting and component replacement "I think" I have it fixed because all voltages (VS, VA, M5V) are present and stable when plugged into AC only. However, when I connect the y-sustain board the clicking returns. I'm fairly certain that there is a problem with the VS line in the y-sustain board. Before I start troubleshooting it, I want to make sure the VS, VA, and M5V lines of the power supply are operating correctly under an appropriate load. Is there a way to load test each of these output lines from the power supply using resistors? I'm especially interested in what size wattage resistors to use. The power supply has the following ratings listed on it.

VS: 206V -1.6A
VA: 60V - 2.0A
M5V: 5.1V - 3.0A

Thanks,
sluhbmet

[tom66]

Re: LG 50PJ350 Power Supply Repair

You can try using a 230V lightbulb, rated for 100W or so. That would represent a moderate (ordinary TV picture) plasma panel load. For VA - maybe using a 120V bulb would be OK, two in parallel would draw ~0.83A.

[sluhbmet]

Re: LG 50PJ350 Power Supply Repair

Tom66,

Thanks for the quick reply. I went ahead and tied two 100 watt bulbs in series and ran them on the VS output for about 30 minutes. Bulbs were bright and the voltage held steady. Now on to the y-sus board.

Thanks again.

[waitery]

Re: LG 50PJ350 Power Supply Repair

Hi Tom,

I have this same LG set as well (50PJ350) and I recently put in a new power board after the screen went dark and got no sound. After putting in the new board, I still get no video, no OSD, but now I get static through the speakers, which is different than before. The static sounds like "snow" when you change channels with no input connected to it.

I have taken the voltages off the top off the rail and they are all solid and stable (VS=207, VA=60, M5V 5.1, etc), plus ALL the fuses on the power board, and all the sustain board show continuity and are not blown. For what it is worth, the main board shows the optical out glowing when the set it on. Lastly, when I try and use the remote to change to a different channel or input and I get nothing.....no flash on the screen, no image, no light at all on the screen. I fear that I have a bad panel, but was hoping that you could help me perform some further troubleshooting before I jump to conclusions. Thank you for your time and consideration in advance.

[capkid]

Re: LG 50PJ350 Power Supply Repair

Have you checked your Y-Sus (-Vy and VSC) and Z-Sus (Vzb) output voltages? Also, see the attached control board check.