42PC1DA Plasma partial picture?

[FlatOverCrest]

Hello, I am very new to the world of Plasma TV repair but have some experience and tools available. I was given a LG 42PC1DA Plasma that was having some issues.

I have checked for bad caps through visual inspection as well as physically feeling them. I see nothing unusual.

All tube fuses are in working order

I have checked voltages going into the boards and they seem to be perfect.

I do not have an oscilloscope handy but do have other tools (DVOM)

I first wanted to post up some pictures to see if anyone has seen this problem before? Typical failure with this model seems to be a black screen with sound. I have a moving picture on some of the screen after a very short warm-up (within a min) period.

Is there a recommended testing procedure I should be following step by step? A repair manual that is out in the community?

Is there anything else I should be replacing while i'm in there? I know this thing is old but they seem relatively robust.


This is right after turning the set on.


This is after switching to the menu (almost immediately)


This is the menu screen after about one minute


This seems like a great community, I would truly be grateful for any assistance anyone can give. Thanks!

[FlatOverCrest]

Re: 42PC1DA Plasma partial picture?

A little update: Adjusting -VY had the most profound effect. If I cranked -VY slightly over the -200v mark I could get a full picture it was just fuzzy and lacking any contrast.

These symptoms have to mean something to someone. I am going to keep my head down but as of now I am not sure what to test.

Any help would still be greatly appreciated.

[tw2005]

Re: 42PC1DA Plasma partial picture?

Check the ZSUS, dim,dark splotchy picture would be a ZSUS issue i expect. check the voltages there too.

[Alastair E]

Re: 42PC1DA Plasma partial picture?

Check voltages across the red film caps on Ysus and Zsus...

Should be between 90-130V.

Suspect Zsus IPM failure.....

[FlatOverCrest]

Re: 42PC1DA Plasma partial picture?

Thanks for the direction! I will check them out and report back!

[tom66]

Re: 42PC1DA Plasma partial picture?

Also Ysus film cap should match Zsus film cap voltage within about 10V.

[FlatOverCrest]

Re: 42PC1DA Plasma partial picture?

Okay. Here is an image of my Zsus board. I believe I measured the proper red film caps. they were quite low if they were the correct caps.... The readings are in the picture. Are these the proper caps?

[Alastair E]

Re: 42PC1DA Plasma partial picture?

Yup--Those are the caps--Sorry, should have said they are in parallel, so you only needed to measure one in the row!

The two lower ones do a different function I think, but by the look of it, you have no energy-recovery happening on that Z-SUS board,--this could be because there's no energy to recover--or the ER circuit for some reason --isnt working.
--BTW-- do the two fuses check OK?

Have you checked the VZbias out of curiosity?--measured at the tab of that Transistor to the right of that sub-board...

How was the voltage on the same row of caps of the Y-SUS?

[FlatOverCrest]

Re: 42PC1DA Plasma partial picture?

No need to apologize!

Might be getting somewhere.

Ysus looks good. measurement below:



However. I had measured the Vzbias this am per the manual I had and it was in spec. 100v. now it is only reading .002v see image below for measurements at the Zbias collector to ground and at the fuses.



Vzbias went from 100v this am to .002v now measured from collector to ground (forgot to add that to the image)

These measurements have changed since I started! At some point the lower fuse (60v circuit) has popped on Zsus! I know all tube fuses checked out when I started, and they were all perfect. Ahh!

[FlatOverCrest]

Re: 42PC1DA Plasma partial picture?

This is what Zsus is looking like now (shorting out)

[Alastair E]

Re: 42PC1DA Plasma partial picture?

Hmmm....

Before replacing the fuse--its worth checking the Z-SUS IPM under that heatsinks for shorts, and for any shorts on the Va (60v) circuit of the Z-SUS board.

Fitting a new fuse can sometimes cause more damage, the fuses are rather highly rated IMHO, and can cause more troubles....

Its looking like the IPM is faulty on the Z-SUS board.....

[Alastair E]

Re: 42PC1DA Plasma partial picture?

Ah--the second pic illustrating the short of the Va fuse didnt show when I saw your last reply...

How are you at fault-finding and pulling/replacing parts on PCB's?

[FlatOverCrest]

Re: 42PC1DA Plasma partial picture?

Fault finding might be okay if I know what to check. Lets say so so... replacing parts I actually feel fairly comfortable with.

[Alastair E]

Re: 42PC1DA Plasma partial picture?

Well--you'll have to trace what that fuse supplies and check for the short.

This will involve removing various items connected to that line, checking them and the line for the short...

Prime suspects would be any semi-conductor device, including any that are on that sub-board.....

[tom66]

Re: 42PC1DA Plasma partial picture?

On these sets, Va travels straight to the X-buffers, the Z-sustain does not use it. There may be some decoupling capacitors but that is all.

[Alastair E]

Re: 42PC1DA Plasma partial picture?

Ah--So, disconnecting the board from the X-buffers will rule them out....

[FlatOverCrest]

Re: 42PC1DA Plasma partial picture?

Is it fairly hard to find a schematic on this board? I am honestly a little unsure on what to check without following traces.

Would purchasing the whole board be a bad idea? I was really looking forward to doing some soldering work but this seems like good value http://www.coppelltvrepair.com/p/472...change-service

[FlatOverCrest]

Re: 42PC1DA Plasma partial picture?

I have the board out now and I am trying to track down the short. I am not having much luck. Any ideas? I am not really sure what to test to be honest.

[Alastair E]

Re: 42PC1DA Plasma partial picture?

Unfortunately--there's no schematics of the actual boards around--outside of LG, and they aint letting anyone see 'em....

Only way to trace that short is to check out the printed traces --as best you can--look for caps connected between the Va track (that fuse) and the Gnd/groundplane tracks.
--This can be difficult as these are multi-layer boards!

Just make sure the short is still present, now the board is disconnected from the set first.

Some random checking of caps and components may be needed, there's not that many parts on that board, prob take a half-hour to check most suspects....
--Better than laying out near a hundred bucks....

Only way I'm sorry.....

[tw2005]

Re: 42PC1DA Plasma partial picture?

Not sure if this will help, very basic checks in diode mode.