LG 50PQ30 Plasma

[1997eclipsegst]

Hey everyone,

I am working on a LG 50PQ30 Plasma. I picked this up from a guy stating that it needed a Y-Main, upper and lower buffers. The set was apart when I picked it up. I got it home and tested the buffers and found they were both good. The Y-Main that came with this set had the fuse jumpered so I didn't try this board. I have a working Y-Main out of a Sanyo 50DP749 that had a bad panel and lower buffer. The upper was ok and had half of a picture. This set uses the same internals. I checked to make sure everything was plugged in and fired it up. The set came on and showed the channel and snow (no video source to the set), then 10 seconds later it shut down. Try to turn it on and does nothing now. I tested voltage on the VA and VS, The voltage goes up to the panel voltage listed then drops to zero. The Z-Main is linked off the Y-Main. Tried to unplug the Z-Main and no change. Unplugged the Y-Main and the power supply stays at the correct voltage. I connected everything back up and tried to disconnect the upper and lower buffers one by one, and both together and still goes into protection. I checked the Y-Main that came with the set and doesn't work either. Anyone have any ideas of anything else to check on this? I found a couple Y-Main boards on ebay but don't want to kill a $80.00 board.

Thanks in advance!

[Baileybum1234]

Re: LG 50PQ30 Plasma

You sure its a Sanyo 50DP749 bud? I cant find nothing on this TV on the net.

[1997eclipsegst]

Re: LG 50PQ30 Plasma

Oops... I put that down in the wrong order. It is a DP50749. I started checking the Y-Main for shorted components and found two 45F122 in locations EY725 and EY727 shorted. I also checked the original Y-Main that came with the set and has the same 2 shorted. I had a parts board that had these components on it. Replaced the 2 on board out of the Sanyo and has been working fine for the past 30 mins. Not sure what happened the first time? But I am glad to see it work. I am going to replace the components on the other board and see if that one works as well.

[1997eclipsegst]

Re: LG 50PQ30 Plasma

Well I had the tv running for over 6 hours and was working fine. I decided to fix the original Y-Main that came with it that had the same two 45F122 in locations EY725 and EY727 shorted. I took the good working Y-Main out and swapped it with the one I just fixed, tried to turn it on and it did nothing, then clicked off and went in protection. So I removed that board and put the working board I just pulled out, turned it on and now all it does is flash different colors from the panel.

Video of the flashing:
http://s658.photobucket.com/albums/u...ps80f5972d.mp4

I pulled the buffers back out and tested for shorts and didn't find any.
Tried another control board, No difference

I am guessing this Y-Main may have quit as well. Anyone thoughts?

[tw2005]

Re: LG 50PQ30 Plasma

Is the the Ysus all bolted in and earthed correctly? I did something silly like not putting all the screws in a LG 50PK550 and it did something really funky like that, maybe not as extreme. I had some earthing points unbolted.

Might seem a silly question but I had to ask.

[1997eclipsegst]

Re: LG 50PQ30 Plasma

I will have to double check that when I get home from work. Not a silly question. I appreciate the advice.

[tw2005]

Re: LG 50PQ30 Plasma

Sometimes i've done some real silly things like that when rushing things. Last week I was busy rebuilding some SC boards and on one occasion I forgot to put the earth screws in the buffers. needless to say it came on dimly and shutdown.
It's the family Tv, irate Mrs and a couple of deep breaths later i discovered my error but it freaked me out and i thought I had stuffed it. LOL

[1997eclipsegst]

Re: LG 50PQ30 Plasma

Well this is interesting. I checked the Y-Main and buffers to be sure all the screws were all installed and tight, which they were. I powered up the set and did something different then what it did last night. I can see the panel prime, then it has multicolor sparkles all over the screen that seem to change with whatever image it is trying to show. Sound still works fine. Checked voltages and all are within panel specs. I pulled the upper and lower buffers to double check for any shorts and they were fine as well. I pulled the Y-Main and none of the components attached to the heatsinks are shorted either. Not sure where to go from here.

[tw2005]

Re: LG 50PQ30 Plasma

Maybe dig through this as it has plenty of checks listed you could try.

[1997eclipsegst]

Re: LG 50PQ30 Plasma

Sounds great. Thanks for the manual. I will check it out sometime this afternoon and report back if I find anything different.

[tw2005]

Re: LG 50PQ30 Plasma

They have a couple of notes about checking for broken solders if the buffers/ymain have been replaced- if your lucky?

[1997eclipsegst]

Re: LG 50PQ30 Plasma

Just wanted to update this. I did get the tv running again. Thanks again TW2005 for the manual and suggestion on checking for broken solder joints where the buffers meet the Y-Main.

I pulled the Y-Main out and was checking for broken solder joints and found the problem. It ended up being something that I did. When I pulled the Y-Main apart from the buffers still attached to the set I hit one of the stand offs and it broke a tracer going to the top buffer which links to the bottom buffer causing all the problems. Soldered a jumper in and has been working great since.

Thanks again to everyone on this great forum!

[tw2005]

Re: LG 50PQ30 Plasma

Just wanted to update this. I did get the tv running again. Thanks again TW2005 for the manual and suggestion on checking for broken solder joints where the buffers meet the Y-Main.

I pulled the Y-Main out and was checking for broken solder joints and found the problem. It ended up being something that I did. When I pulled the Y-Main apart from the buffers still attached to the set I hit one of the stand offs and it broke a tracer going to the top buffer which links to the bottom buffer causing all the problems. Soldered a jumper in and has been working great since.

Thanks again to everyone on this great forum!

That's gold. Nice skid mark on the board & definitely an air gap there. Probably not quite what the OEM was suggesting to check, but damn how lucky was finding that in the process

[1997eclipsegst]

Re: LG 50PQ30 Plasma

Yea I am glad that is all it was. At first when I seen the scrape over to it, It didn't look like it was broke. Checked continuity and sure enough it was. The pic was after I scraped a little more off to see the break.

Thanks again for your help with this.

[tw2005]

Re: LG 50PQ30 Plasma

Yea I am glad that is all it was. At first when I seen the scrape over to it, It didn't look like it was broke. Checked continuity and sure enough it was. The pic was after I scraped a little more off to see the break.

Thanks again for your help with this.

You're welcome.
I've been in a few situations where induced faults have occurred during maintenance. Always suspicious when a known working item stops working after a simple remove and install. My gut was telling me something had lost connection.

Top job belling it out, only true way of being sure. Love it

[johnboy1313]

Re: LG 50PQ30 Plasma

I got it home and tested the buffers and found they were both good.

Out of curiosity, how do you test the buffers?

[tom66]

Re: LG 50PQ30 Plasma

Nice fix! Picture looks good even on a crappy LCD monitor.

Buffer testing:-
https://www.youtube.com/watch?v=51SZsfH60EY