LG 50PG20-Ua blows mosfets and fuse

[Old Buzzard]

I am a newbee to repairing plasma tv's.I have an Lg 50PG20-UA that i have been working on. When I first got it and removed the back noticed that a few caps were bad.I pulled the power supply and replaced the bad caps, 5amp and 10amp fuses. The last person to do any work on this set just soldered new fuses on top of the blown ones,so I replaced them the correct way. I also noticed that they had replaced a few other caps also. I just hope they replaced them with the correct sizes. After replacing the PS I plugged it in and powered it on. It turned on for a few seconds then shut down and wouldn't power up again. I pulled the PS again and found that the 10amp fuse had blown and 2 mosfets had shorted out. Ordered more from Digi-Key. When I recieved them, I put the PS back in and it did the same thing again. I ordered extras,so I replaced the shorted mosfets and blown fuse. This time I unpluged the Ysus board and the Zsus board. It powered up and stayed on. I checked all the power readings and they were right on the money. I hooked up the Ysus board and powered it back up leaving the Zsus board unhooked. It powered up and stayed on. I then hooked up the Zsus board and powered it back on again and it blew the mosfets and fuse again. I purchased a replacement Zsus board on Ebay thinking that my board was bad. When it arrived I put it in and powered it on. Again it blew the mosfets and 10amp fuse. Getting a little flustrated at this point!! Now I'm down to my last set of mosfets and fuses. I have checked both boards for shorts to ground and haven't found any. I put everything back together and unhooked the Ysus board just leaving the Zsus board hooked up with my fingers crossed. It powered up and stayed on. So now I can hook up either board alone and it powers up and stays on just fine, but not both boards. What would cause this set to blow the mosfets and fuse when both boards are hooked up?I hope I have explained everything OK.

[ratdude747]

Re: LG 50PG20-Ua blows mosfets and fuse

Moved out of FAQ.

[tw2005]

Re: LG 50PG20-Ua blows mosfets and fuse

Have a look at this, may help. I'm thinking it's not going full power until both boards are hooked up and that's when it blows. Have you checked that Vs and Va are there when either board is connected and it does not blow?

There's a PSU standalone test and hoping it's the same boards you have.

[Old Buzzard]

Re: LG 50PG20-Ua blows mosfets and fuse

Thanks for the responce tw2005!! I have measured the voltages with one board or the other installed as well as without any boards installed. The voltages are the same no mater which way I try it. They are; Va 65,Vs 193 and 5V. I've been afraid to try both boards again,as I'm down to my last mosfets. The attachment you sent will no doubt help as far as troubleshooting goes. I will read it and try some of the tests. It appears to draw more power than the power supply can handle when both boards are hooked up. I just have to figure out what is causing both boards to draw too much power.

[Old Buzzard]

Re: LG 50PG20-Ua blows mosfets and fuse

I tried a few of the tests for the Ysus board and the Zsus board,as far as voltages. I just had the Zsus board hooked up and the bias voltage was 89v and the label says 100v. I ajusted it up to 100v. I then diconected the Zsus board and conected the Ysus board. The Vy voltage was 197v and label says 195v,so I ajusted it to 195v. The Vsc voltage was what the label says it should be. Do you think that little amount of difference would make it blow the mosfets and fuse? I'll keep testing and reading.

[tom66]

Re: LG 50PG20-Ua blows mosfets and fuse

What is the panel's Vs rating? Is that in spec?
Such small changes would only cause picture issues, not mosfet damage.

[Old Buzzard]

Re: LG 50PG20-Ua blows mosfets and fuse

The sticker on the back of the tv say Vs is 193v,and that is what I read on the Vs leads. All the voltages are what the sticker says they should be. Thanks for your responce!!

[selldoor]

Re: LG 50PG20-Ua blows mosfets and fuse

If it is the Mains fuse that keeps blowing you should try connecting a 120v 60w filament
bulb instead.

[Old Buzzard]

Re: LG 50PG20-Ua blows mosfets and fuse

My mistake!! I stated that the 10amp fuse was blowing,but it's the 5amp fuse that keeps blowing.My fluke meter is capable of reading amperage, so I tried reading the amperage when one board was hooked up and then the other board. The highest reading I could get was 1.5 amps. When you add the 2 boards toghether it doesn't even use 4 amps, so why is it blowing a 5 amp fuse? Without a wiring schematic it's hard to say what all is running off that 5 amp fuse. Would anybody know where I could get a copy of the wiring schematic for this power supply? There are 2 different number on the board; EAY41360901 & YBIK501705.

[LDSisHere]

Re: LG 50PG20-Ua blows mosfets and fuse

Schematics may be hard to find for this power board. If could you post clear, detailed pictures of the front and back of the power board and indicate which parts you replaced, it would make it easier for forum members to help you.

[CoppellTVRepair]

Re: LG 50PG20-Ua blows mosfets and fuse

Here, thope these can help:

http://www.coppelltvrepair.com/search?q=EAY41360901