LG 50PG1000. Bad YSUS? Strange image behaviour

[dabyd64]

Hi all.
I got a LG TV model 50PG1000 for free from a friend. He said, "If you fix it, it's yours!"
Well, I though it was going to be something easy, like a bad cap or shorted diode on the PSU...but nope

The TV's led powers on (green) but no image.
I have read about PDP servicing for a week or so, in my spare time (that means 15-20 minutes a day...), so:
I disconnected the upper Ybuffer board, and after powering it, some kind of image comes out after 1-2minutes. All almost white and lots of strange dots moving everywhere (noise?).
I put a jumper on the EX_AUTO_GEN pads to enable the test pattern generator.
The white comes ok, the red also seems good. The green and blue have some noise dots. And the coloured images shows washed out.
The colours bar pattern appears but also looks weared out.

I made a small video, I hope it helps.Check 1080p for better quality
http://www.youtube.com/watch?v=pHpRsoFX6Uc

By the way, I've worked some years with electronics, but never with plasma displays, so I'm used to multimeters, oscilloscopes, serial ports, JTAG...but I'm a completely noob with this

Cheers everybody

[tom66]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

Bad buffer; probably the top buffer, but a good idea to replace both. Check Y-sustain -Vy and Vsc, but the buffer should be the only problem.

Check the PDP model number on the LG panel sticker (inside the unit, on back of metal plate), something like PDP50G4000.

[dabyd64]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

Thanks Tom!
That image in the video is without the TOP buffer.
Does that mean that both top and bottom buffer boards are bad?
And yes, all voltages are good. Adjusted few volts, but they all were good (Panel requires 194V, 60V. They were 192V, 58V, don't think it would cause such problem)
all the Mosfets, diodes, fuses...are Ok on the YSUS.

[tom66]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

You have a scope available at the moment?
What's it look like with the top buffer - no power?
If so, the top is bad, and the bottom is probably OK.

[dabyd64]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

I got a scope, but it's analog, I can't store the signal, which makes hard to find out what happens there.
The power is ok in all circunstances, always green led.
With the top buffer, it makes no image.
With both buffers, no image.
With only bottom buffer...bad image.

[tom66]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

The top buffer is probably bad.

An analog scope is fine for plasma troubleshooting. You need one which has a 400V or more rated input and a (fixed) 10X probe.

[dabyd64]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

Thanks. That weird image from the bottom buffer is normal?
My oscilloscope is 400Vp rated, also has 10x probes.

[tom66]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

Without the top feeding in the synchronisation signals, the bottom will go crazy.

Each buffer chip is basically a shift register.

Say a "1" connects the line on the plasma panel to Y-sus out, and the "0" connects it to the -Vy voltage. (-180V or so.) -Vy selects the line, so that an image can be programmed onto that line, and the Y-sus out is connected when the image is to be sustained (made to appear.)

The ICs have a clock, data, reset and output enable.

Data to select each line one after another (0001000 then 0000100 etc.) is loaded in. However, if the data feed is missing, then ALL the lines will be selected, and all the data is loaded at once on every line (so you see lots of vertical lines as the data is copied down the panel.)

Make some sense?

[dabyd64]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

Oh, that are great news! Thanks! I had doubts about that.
I won't buy the entire board. Instead, I'll change the buffers.
It got FE3407F buffers.
I found that FE3407F=FE3298F=SN755882=AN16379A

They are crazy cheap..only $2 each!
I need 4 ics, so I'll buy this:
http://www.ebay.com/itm/5PCS-IC-FE34...item43b3f80e15

10$ for all. Cheaper than $80 for the board!

[tom66]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

Definitely, but beware: they're not easy to change. They've got a large heat pad on the bottom, which is a bastard to fix. You must remember to add the insulating epoxy to the pins after putting the new chip on, as it prevents the high-voltage difference (up to 200V between pins) from arcing over.

[dabyd64]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

Oh, don't worry. I got a 4800W BGA rework machine at the work which can heat up almost anything.
In 12-20 days I will receive the buffers, once I change them I will write here if it got fixed...or not hehe.
Thanks for the help Tom!

[tom66]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

Good luck

After you do that, you can tweak the panel for better black levels, higher contrast, if you want.

I'm making a video on doing it with a Panasonic, but it'll also apply to the LG.

[dabyd64]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

Interesting! I'll try it for sure if I got it fixed

[Jurki]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

Interesting! I'll try it for sure if I got it fixed

Did you repair it?

I have same TV, with same issue. I made a DATA signal bypass to bypass 2 upper buffer IC and now I have image on bottom 3/4 of display.

I'm asking you if you are success, because I heard, that if buffer IC is wrong, usually it happened because PDP display is deffective.

[tom66]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

On these sets PDP panel failure causing buffer IC failure is rare. Buffer ICs on these just fail for some reason.

[Jurki]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

On these sets PDP panel failure causing buffer IC failure is rare. Buffer ICs on these just fail for some reason.

Thanks for info. And what about your case? Did you replace buffer IC (FE3407F) ?? Did your TV works after your repair? IF yes, how long ?

I found those buffer IC on ebay, but it usually takes about 2 months to arrive to europe.

[tom66]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

Haven't done one of these myself. That's just what others have found. The repair of buffer ICs generally works.

[dabyd64]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

Hi! Few time after this I started both studying and working, so my free time is a ****. Sorry for being away!
I had removed the buffer ics, all went ok but one, which was stick like hell, and broke some pads..,
I put the new buffers, then I left it for some days, until I had time for repairing the broken pads.
When I took it again, the pins of the new buffers were oxidized with a green dust over all them.
I think it was caused by the flux, I didn't clean it carefully.
Since then I gave up for a time, I didn't want to spend my almost inexistent free time on that TV
And then I forgot about than for some months, until today when I received a forum email!

So maybe I'll end buying and entirely new board...

[Jurki]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

Hi! Few time after this I started both studying and working, so my free time is a ****. Sorry for being away!
I had removed the buffer ics, all went ok but one, which was stick like hell, and broke some pads..,
I put the new buffers, then I left it for some days, until I had time for repairing the broken pads.
When I took it again, the pins of the new buffers were oxidized with a green dust over all them.
I think it was caused by the flux, I didn't clean it carefully.
Since then I gave up for a time, I didn't want to spend my almost inexistent free time on that TV
And then I forgot about than for some months, until today when I received a forum email!

So maybe I'll end buying and entirely new board...

I fully understand your free time problem. I'm almost same, but I want to solve it ASAP as TV is too big to left it in corner in living room for long time as I live in flat...

Do you have some spare buffer IC? I need only 2 pcs. I don't want to wait 2 months for it from ebay..

I still did't remove a heatsink from buffers. Do you know what is a glue type on it? It looks like cheap hot glue stick. It should be enought isolant too.

I look over several websites offering whole Y buffer, but it's about 50-70eur. And I'm afraid that real problem is on PDP panel, and new buffer will be damaged again in short time. And it is 70eur waste on old TV.

[dabyd64]

Re: LG 50PG1000. Bad YSUS? Strange image behaviour

I had bought 5 buffers, used 4 on the ysus board, so sorry I have only one!
The glue is thermal adhesive. With a shap knife and care is easy to remove.
Then there is hv silicone over the buffer legs, I removed it with a plastic card.
I would remove these buffers first and fully clean the board, before buying anything. Because I didn't, now I have to buy the board, and the money of the new buffers is wasted.