Plasma LG 50pq2000 sound ok but no screen

[trosdepep]

Im trying to repair this Plasma.
The sound is ok but there isn´t screen. When turns on the screen is a few seconds with light turns of, only the screen, and sound works.
When i disconect top buffers, half bottom image appears.
When i disconect bottom buffers, half top image appears.

Can help me?

Thanks

[tom66]

Re: Plasma LG 50pq2000 sound ok but no screen

So, in a dark room is there any slight glow visible from the display?

[trosdepep]

Re: Plasma LG 50pq2000 sound ok but no screen

So, in a dark room is there any slight glow visible from the display?

At first, yes.
I was this morninsg proving, connecting and disconecting wires, always with switch off, and now is completely dark.
The middle screens are defective with red dots and there are two resistors of 10 ohms on z-sus that takes smoke in a few seconds (are marked in the picture)
I had a spark when y conected the wire from supply board to z-sus (always switch off) a dischargue of caps i supose.

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Sorry for my english.
Thank you.
This picture is z-sus?

[tom66]

Re: Plasma LG 50pq2000 sound ok but no screen

Yes, that is the Z-sustain.

If you have a slight glow with red pixels, I suspect the Z-sustain.

[trosdepep]

Re: Plasma LG 50pq2000 sound ok but no screen

I think I've explained badly.
At first of the morning had slight low and when I disconnected one of the buffers had middle screen (perfect image) two middles works.
What is the problem at first?. Z-sustain?. Both buffers works fine separately but no works together.

Then i´ve been playing and proving.

Now there isn´t sligtht low when swicth on, is dark. When i disconnect one of the buffers appears middle screen, the image appears, but has color defects with red dots and the R´s smokes.
Now there are two problems? Z-sustain and anything more?

What have I touched, so that the image is now defective?

Do you think with the z-sustain replacement, tv work fine?

Thank you very much.

[tom66]

Re: Plasma LG 50pq2000 sound ok but no screen

I have never encountered a TV which works when either buffer is not unplugged so I can't offer much advice -- it sounds more like a connection issue or a power supply problem.

Did you disconnect the board while the TV was running? As that can cause a problem...

[trosdepep]

Re: Plasma LG 50pq2000 sound ok but no screen

I was reading information about breakdowns on plasma tvs. Usually, when there isn´t screen, the failure are buffers, top or bottom, y-sus broken and if disconnects the broken, then works the good middle. But in my case, both buffers are good because works separately (no together).

I never disconnected or connected cables with switch on.I switch on tv several times with some cable disconnected...

[tw2005]

Re: Plasma LG 50pq2000 sound ok but no screen

Try this training manual. it has a lot of information and has tests and results for the boards and individual components.
The ZSUS gets power from the YSUS and I have had an old 50PX5D with the same setup (obviously completely different boards) which had two 10ohm chip resistors on the ZSUS which would smoke and in my case it was actually a bad YSUS which must caused it because when i got a working YSUS, they stopped smoking and the TV worked although the ZSUS did end up arcing to the chassis from the IPM modules and died.

Never did get my head around as to why, but you'd think it was the ZSUS seeing those resistors smoke.

I suspect a sloppy soldering job by the guy before me and the pins arced but I can't be 100% sure.

The fact it will not run with both buffers has me puzzled but that also leads me to suspect the YSUS.

This manual also shows how to test the SMPS on it's own too so worthwhile checking that out too.

Your ZSUS may also now be damaged if your saying you can't get a picture anymore but hopefully with this manual you can at least check out the components on the Y as well and confirm whether it is suspect or not and likewise for the ZSUS.

It's for a different model but uses the same boards and panel I believe so should help.

edit: I'm still reading this but this is one of the best manuals I've seen. It shows you how to even test the ZSUS with the YSUS disconnected so i hope you can follow it as it may save you $$ by not purchasing boards you may not need.

At the end of the manual there's some quick tip fixes and scenarios. Check them out too just in case that's what your seeing. Also give procedure for running with either buffer boards disconnected.

[trosdepep]

Re: Plasma LG 50pq2000 sound ok but no screen

It's amazing this document. I looked it over and there are many things I do not understand:

Where it says, diode test, refers to putting the multimeter in diode, but the board must carry current?

From what I've seen above, all voltage tests are done with all boards interconnected with each other, except that they can test SMPS unconnected except two 100w bulbs in series and AC
How I can test the Z-its without burning the Rs?

Thank you for this valuable document.

Forgive if questions can be ridiculous, but I am also an amateur and beginner

Any advice is welcome

[tw2005]

Re: Plasma LG 50pq2000 sound ok but no screen

Good morning. I'd say if you follow the ZSUS standalone test as per the manual and they smoke then that board has an issue.

Why not test all the diodes and transistors first before applying anymore power to it as we really don't know it's current state. I would assume all tests are without power except if it's telling you to measure a voltage.

Diode mode would be Multimeter in diode mode but you would do these with no power to the board. You may have to remove the component to get a true reading. I only glanced over the document so they may or may not point somethings out as there is probably an assumption of basic knowledge since it's written for technicians.

You can always replace those resistors if need be if you repair the board at component level.

Just remember if you've powered it up recently the capacitiors will hold charge and theres some high voltages lurking.

Good luck with it, gotta go. It'll be an intersting read to see what you find.

[trosdepep]

Re: Plasma LG 50pq2000 sound ok but no screen

I was checking the TV with the help of the service manual and I will tell you some results.

First I connect the tv and hear a buzz that I did not notice the first time, then look at the screen and appear the message "no signal", miracle!, it was repaired? ... but the resistances that I pointed in a red circle began to burn again. I turn off the TV and connect an external video source (DTT) to check if there is image. Turn on and did not hear the buzzing and had no image, only heard the voice of the external source.
I check the voltages of the power supply, all correct.
Then the plate "YSUS" almost all voltages are correct except in some 15v checkpoint marks 5V .
Before checking voltages in the "ZSUS" I disconnect all its cables and then the voltages of the "YSUS" went well and the screen showed the image of tdt. The image was a bit faulty with red dots everywhere like the time when disconnected y-sus up or down.

I guess the conclusion is that the "ZSUS" is bad... what do you think?

I brought home the ZSUS and this morning I have been testing with the multimeter but can not find anything and apparently everything is OK, I think I need a lot of experience.
I need test voltajes on z-sus, I dont know if testing voltages in fets could find the problem.

I've thought about buying the "ZSUS". I've found it on a website for 55 € (no new) but another web has a repair kit for "lg 50pq3000" (will serve for PQ2000?) For 150 € with all boards.

Any advice.

PS: It is normal that the TV works without the z-sus?
If y-sus was wrong, disconnecting z-sus no image appears, right?

[tom66]

Re: Plasma LG 50pq2000 sound ok but no screen

With the Z-sus disconnected you will see a dim picture.
Yes, I suspect the Z-sus, you would need a scope to verify it.

[trosdepep]

Re: Plasma LG 50pq2000 sound ok but no screen

I changed all power transistor of z-sus, 7 igbt, 8 diodes and 3 mosfet and the two resistors marked in the picture.
Everything remains as before but now i always have image because i switch off tv before resistors come on fire.
I´ve tested voltage on z-bias test point (80V is correct). When switch on it marks 83V but immediately changes to 8V, this is the problem...
I have thought to change all caps but they seem to be as new....
I have a fear of if I put a new z-sus board and everything remains the same ...
The problem is there isn´t money. I am using components of another broke panel LG tv (it is new).

[trosdepep]

Re: Plasma LG 50pq2000 sound ok but no screen

I´ve changed all caps and everything remains the same...
I think that tw2005 has reason.
When i disconnect z-sus bus that comes from y-sus through t-con, resistors stops to smoke and VZ-bias turns correct.
Possibly is y-sus problem but i´m little tired... and I will buy repair kit in bixreclamation website for lg 50pq3000 (£89.99 ). It is for panel PDP50G20001, like mine.

Ps: Y-sus heatsinks are warm except the middle one

[trosdepep]

Re: Plasma LG 50pq2000 sound ok but no screen

Well, today I will receive 50pq3000 repair kit.
Any suggestions of the steps I should take.
I think first change the "Y-SUS" and see if it works. If it does not, change the Z-SUS and so on until I get it to work.

Another question. Once I have placed the new plates, I have to wait 15 minutes until hot and then adjust the voltages of each plate:
In the Y-SUS (VY and Vsc)
In Z_SUS (VZB)
Anything else?

Thanks

[trosdepep]

Re: Plasma LG 50pq2000 sound ok but no screen

I just read that when replacing the Y_SUS is appropriate to replace the Y_Buffers because if there is a defective buffer can cause breaking of the new Y_SUS

Clearly, it is best to replace all the plates, but I'd like to find out where the fault was and what the defective board.

[tom66]

Re: Plasma LG 50pq2000 sound ok but no screen

It's only necessary if the Y-buffers are shorted. Remove the buffers and post a clear picture, so we can indicate where to test for shorted buffers.

[vinceroger69]

Re: Plasma LG 50pq2000 sound ok but no screen

just looked at the repair kit looks good has it got every board are they brand new
http://www.bixreclamation.co.uk/LG_5.../p11193_dk.htm

[tom66]

Re: Plasma LG 50pq2000 sound ok but no screen

just looked at the repair kit looks good has it got every board are they brand new
http://www.bixreclamation.co.uk/LG_5.../p11193_dk.htm

Not likely to be brand new, but from cracked screen TVs, often show room models knocked over by customers or damaged in transit so very low hours.

[vinceroger69]

Re: Plasma LG 50pq2000 sound ok but no screen

seem good prices on the boards not sure on delivery costs though.