LG 50PC5D YSUS/ZSUS Issues

[YamahaFreak]

I have acquired this TV from a neighbor, whom said it did the 'pop of death', and now it works without a picture. I looked up info online and apparently the Y-Sustain and/or Z-Sustain boards like to fail in a manner that necessitates replacement of the whole board. I tried feeling the heat sinks to see if they're getting warm, and it appears that perhaps one of the two on the YSUS board isn't as hot as the others. What I'd like to know is if there's a more accurate way to know which of the two boards (hopefully not both!) are failed. The TV has run for several hours now without issues, other than no picture, obviously.

[drussell]

If it is one of the models with IPMs, they often fail but I've successfully replaced just the IPM instead of the whole board. A blown IPM will generally fail shorted so will blow a fuse, usually a 4A ceramic 5x20mm, so check fuses first on the Y-Sus and Z-Sus boards. If one has blown, check for a short on that board, typically Vs to ground is what shorts due to a blown FET/IGBT. If this model uses IPMs, the blown FETs will likely be inside the hybrid module, requiring replacement (though some people have bodged on new external FETs ). It's a straightforward task with some solder wick and a decent iron, though a desoldering station is quicker.

If the fuses are all good (look for surface mount ones, too), move on to standard plasma troubleshooting... Check your high voltages... The Vs and Va testpoints are usually on the power supply board and the other voltages on the LGs are usually called things like -Vy on the Y-Sus and and Vzb on the Z-Sus board in LG parlance.

The proper voltages will be on the panel sticker and, IIRC, the second line on the LG stickers below where it calls out the Va (the address voltage for the X boards at the bottom) and Vs (the sustain voltage that does most of the power, comes out the Y-Sus board through the Y-Drives) goes in this order: Set-Up / -Vy / Vsc / Ve / Vzb

Some of these will probably be missing and say N.A. on the sticker as most LG sets do not have all of these voltages but they have maintained the sticker format. Just look for the test points for each and see what voltages you actually have at the testpoints, then I can point you in the right direction for troubleshooting that section.

Vs and Va may only come up for a few seconds at power-on if it senses a fault and goes into protection but you should have time to measure them. A MAX function if your multimeter has one can be helpful.

The service manual is avilable at:
http://www.toms-service-manuals.com/...&mfg=LG-Zenith

[YamahaFreak]

Thanks very much, Drussell! I have tested all fuses on all boards (including one each surface mounts I found on the Y and Z boards), and all test good. Now, I am having difficulty locating the test points on the power supply. I'm used to them having 'TP' prefixes, and I'm not seeing anything like that.

[drussell]

Originally Posted by YamahaFreak

Now, I am having difficulty locating the test points on the power supply. I'm used to them having 'TP' prefixes, and I'm not seeing anything like that.

I've never worked on this model so I can't say for sure, but taking a quick look at the service manual there are several different possible power supplies and, indeed, it looks like there aren't test points for the Vs and Va. You're supposed to just stick your probe into the back of the output connector. (There should be a silk-screened legend beside the connector.) Your negative multimeter probe can just go to any convenient chassis metal like one of the wallmount holes as the chassis is at circuit ground potential. Vsc/Vscan is usually one of the only ones that you measure across a resistor or capacitor rather than to ground as it is floating.

If you have a decent camera, perhaps you could post a couple good close-up pictures of the various boards and one of the whole back of the TV so I can see what we're dealing with and how everything is interconnected.

[Findm-Keepm]

I've got the service manual - lemmed klnow if you need it - FREE. Don't pay for it - LG gave it away for free for over 2 years, and then took them off the web. I have a little over 300 LG LCD/plasma/DLP and Zenith CRT sets data, all free from the old LG FTP site.

The manual for the 50PC5D is over 30 megs in size, so a high-speed (DSL/Cable) connection will be needed. I don't have a server, but may be able to upload it to a church website I manage.

PM me if interested.

[YamahaFreak]

I'll see what I can do with this iPhone, though unfortunately it only allows me to add one photo per post. My power supply's part number is (I think) 2300KEG006C-F. I've attached a photo of the upper left connector, showing the silkscreened voltages. (The connector is unplugged in the photo, for better visibility.)

[YamahaFreak]

Here is a photo of the entire chassis. YSUS at left, power supply in the center, ZSUS at right.

[YamahaFreak]

UPDATE: Vs and Va voltages measure 197V (within 2 volts of rated 195) and 60 (right on) respectively.

[YamahaFreak]

Originally Posted by Findm-Keepm

I've got the service manual - lemmed klnow if you need it - FREE. Don't pay for it - LG gave it away for free for over 2 years, and then took them off the web. I have a little over 300 LG LCD/plasma/DLP and Zenith CRT sets data, all free from the old LG FTP site.

The manual for the 50PC5D is over 30 megs in size, so a high-speed (DSL/Cable) connection will be needed. I don't have a server, but may be able to upload it to a church website I manage.

PM me if interested.

That will be most helpful! I'll get in touch.

[drussell]

Originally Posted by YamahaFreak

UPDATE: Vs and Va voltages measure 197V (within 2 volts of rated 195) and 60 (right on) respectively.

This is with all the board still connected?

If you look at the panel in complete darkness does it have a faint glow when powered up? (IE, is it getting precharge?) Check the rest of the voltages... If you have Vzb (panel bias, on the Z-sus board) then the Z is probably fine and I'm suspecting problems on the Y. Usually if the Z has a problem you will still get a picture it will just be dim and washed out with the panel bias absent.

Something must be missing... If all supplies are there everywhere it is possible that one of the IPMs failed open. They usually short but an open is certainly possible and it won't be generating any Yout signal to drive the panel. Can you post the best shot you can get of the whole Y-sus board? Perhaps I can spot some testpoints for things like the actual Yout signal to the panel.

If it does turn out to be a blown IPM you should check for shorts in the buffers on the Y-Drive boards, you certainly don't want to replace the IPM only to have it blow again due to a failed buffer chip.

Many of the IPMs are potted with a clear potting compound on the bottom and it is easy to see the blown FET/IGBTs from the bottom but it's nice to be sure it's frazzed before you bother to desolder it from the board.

Do you have an oscilliscope?

[drussell]

Originally Posted by Findm-Keepm

I've got the service manual - lemmed klnow if you need it - FREE.

That link I posted above has the service manual and it's free... Though perhaps you have a better one, this one certainly doesn't cover everything.

Perhaps you guys missed the link in my first post?

[YamahaFreak]

Originally Posted by drussell

That link I posted above has the service manual and it's free... Though perhaps you have a better one, this one certainly doesn't cover everything.

Perhaps you guys missed the link in my first post?

I should have mentioned that I couldn't get my device to open that link; it just hung without loading. Sorry about that!

EDIT: The link seems to be working fine now. Odd...

[YamahaFreak]

Yes, those two voltages were taken with everything hooked up. I have not checked any other voltages yet. I have verified that the plasma panel has no glow at all; it appears to be completely off. Where would I be checking for VZB on the ZSUS board? I'll try to get photos of both boards for you.

I do technically own a scope...but I don't currently have access to probes for it, and don't know how to operate it properly...yet.

As an aside, I'm not harming anything else by leaving the set running in its current condition, am I?

[YamahaFreak]

Here is a photo of the Y-Sustain board:

[YamahaFreak]

Next, the Z-Sustain board: