LG 50PJ550 Plasma scerren blur and bleeding

[canadaboy25]

Hey guys,
I have an LG 50PJ550 that I recently picked up and had to replace a power resistor on the power supply to get working. After that it has worked fine for about a week. We watched a movie on it last night with no problem but this morning when we turned it on we got this.

The screen is very fuzzy and has black patches and also very bad ghosting. The first two pictures are without anything even plugged in and you can still see ghosts of the exit buttons from the TV box.

When it was working, it would occasionally act up on the loading screen but I just thought the Apple TV box wasn't playing well with the old TV. However, now it is like this all the time even without anything plugged in.

Any ideas what would cause it to do this overnight without being used?

Thanks

[dick_barton]

Re: LG 50PJ550 Plasma scerren blur and bleeding

Have you checked the solder joints on the Xsus board especially around the coils. Are the Va and Vs within spec?

[canadaboy25]

Re: LG 50PJ550 Plasma scerren blur and bleeding

Have you checked the solder joints on the Xsus board especially around the coils. Are the Va and Vs within spec?

Va is within 0.6V and Vs is within 0.1V so I think they are fine.

One thing I find strange is that the TV was unplugged from all video sources and also unplugged from power for about 30 mins and when I just turned it on to check Vs and Va, the ghost of the TV box menu was still there. I'm not sure what part of the TV is remembering what was displayed but I hope it isn't a main board issue.

Also, I noticed the main board LED is flashing a code. 3 short blinks followed by 2 long ones. I am unable to find the table for decoding the error message.

Aren't the X driver boards the ones along the bottom of the TV? They don't look like they have any through-hole components on them.

[dick_barton]

Re: LG 50PJ550 Plasma scerren blur and bleeding

I believe this is your Xsus board

[canadaboy25]

Re: LG 50PJ550 Plasma scerren blur and bleeding

I believe this is your Xsus board

Ah, I think that is the Z-sus. At least everywhere I read says so and also the board says Z-sus out on the connectors going to the panel.

I checked the joints on the board and they all look fine visually. I suppose I could reflow them as there isn't that many.

I quickly checked some of the large resistors but it is hard to tell as they are soldered in parallel with each other and other components as well.

If you believe the problem is on this board, I will start desoldering components and checking them.

[canadaboy25]

Re: LG 50PJ550 Plasma scerren blur and bleeding

I resoldered both of the large coils on the Z-sus and Y-sys boards. The one on the Z-sus board looked fine, however, the one on the Y-sus board looked horrible and looked like someone already had a go at soldering it.

I resoldered it and plugged everything back in but still the same awful picture.

[canadaboy25]

Re: LG 50PJ550 Plasma scerren blur and bleeding

I did some searching and a lot of people were recommending checking the power supply voltages to fix the snow problem.

Attached are pictures of the 5v rail, Va, and Vs.

The 5V rail looks pretty noisy to me and the "wiggle" on Vs shows up about every half second consistently.

I'm not sure if there is a problem here as I do not know what they looked like when they were good.

[dick_barton]

Re: LG 50PJ550 Plasma scerren blur and bleeding

You are correct in saying Zsus. For some unknown reason I had Xsus stuck in my mind.

[canadaboy25]

Re: LG 50PJ550 Plasma scerren blur and bleeding

Well I marked the original locations of the pots on the Y-sus board and did some tweaking. I was able to make the image *slightly* better, but it is still awful.

Interestingly, when I turned one of the pots up, I could see a blue outline of a news channel logo. Must be burn in from the previous owners.

Since tweaking the Y-sus board helped, wouldn't that indicate a fault with it?

[canadaboy25]

Re: LG 50PJ550 Plasma scerren blur and bleeding

Well, I fiddled with the voltage adjustments and managed to get a usable image.

I ended up turning VS up to just before the point the TV shuts itself down, turned the VY and V_SET_ON voltages all the way down, and tweaked the Z-SUS voltage down a bit. The picture is nowhere near perfect but hopefully it will work until whatever is going out fails completely and I can track it down easier.

Just seems odd to me that I shut it down last night working perfectly and now this all of a sudden.

It's really hard for me to troubleshoot when most of the advice I've seen online that looks to be a similar problem to mine is to "replace the board". Plasmas are getting older and worth less and the boards are getting rarer and more expensive. Also, actually finding the fault is part of the fun for me, so winging boards at it isn't a path I'm going to take.

Also, the service manual for this TV is poor at best. No schematics, no voltage specs, no error code table. The Panasonic plasmas I've fixed have had amazing service manuals with full schematics and PCB views. Shame that is not the same for all TVs.

My next step would be to take good images of the PCB and fully reverse engineer it so that I could at least understand the theory of operation. But I just don't have the time for that right now.

If anyone has any other ideas of things to check before I put the cover on and let it run its course, please let me know.

Thanks!