LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

[Gof]

Hi,

First of all, thank you tom66 for sharing your huge knowledge about PDPs!

I have a problem with my LG PDP. Model name is RZ-42PX11. Maybe you (or anyone else) could help?

The first problem is the black, vertical stripe. It is in the part of screen driven directly from the control board (not from XL or XR boards), from P109 connector. I reseated the flex ribbon, but it did not help. Based on your experience, would you expect one of many ACT549 drivers (I believe they are driving the panel address lines, do they?) to be damaged? Maybe you know which of them drive this particular (P109) connector? Ctrl board PN is 6870QCE016C and the sticker on the left says 6871QCH046C, so it's a bit confusing. Anyway I don't want to replace all drivers, so any hint to track down the faulty one would be helpful... I already have one idea (to display an image where this "black stripe" area is white and measure average input voltages on all drivers), but maybe you could suggest something else?

What bothers me more is a flickering snow when the picture is not bright enough. When I display a white picture, PDP starts working fine. When I display a not-so-white picture, the problem returns. You can see it on the movie below:

http://youtube.com/watch?v=wOOxsIkMdyg

The snow is also present on the black-stripe part of the screen. The snow is always there, regardless of the selected input, and even on the "No Signal" message.

I measured Vs, Va and +5V voltages. They all are in spec when the black image is displayed (Va = 64V, while 64.4V is expected, Vs = 190V, exactly as expected). With the white image, Va drops to 62V and Vs stays at 190V.

I watched these voltages on the oscilloscope and Vs and Va seem to be clean. +5V is noisy, but first - I think that this is due to lower oscilloscope range (2V instead of 20V for Va) and second - would such noise on +5V line make a difference? I believe this line powers the digital part, not the analog, and the digital part seems to be working fine (it doesn't hang etc).

I also looked closely at the electrolytes on the PSU board and other boards. They seem fine - no leaks, smooth top surfaces.

Do you have any suggestions what should I do next?

Cheers.

[Alastair E]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

I think I would be more worried by the vertical black stripe than anything else at this stage.

Ive not had a COF chip fail on one of these old (V7, V8/X3) LG sets, but this symptom is often caused by a faulty COF chip, and is sadly Not repairable.

You can check the small plug to the COF Chip film connector that's immediately under that black stripe, re-seat it and hope for the best--With luck you'll get lucky.
--IF its the Chassis I think it is, you'll need to carefully remove that long finned heatsink to gain access to the COF chip to lower-buffer-board connectors....

Any burning or damage to that Mylar film that has the chip on and its the end of days for the set as its made as part of the PDP panel.....

[Gof]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

Ive not had a COF chip fail on one of these old (V7, V8/X3) LG sets, but this symptom is often caused by a faulty COF chip, and is sadly Not repairable.

So there's a COF there that drives address lines... I thought the flex connects directly to the panel.

IF its the Chassis I think it is, you'll need to carefully remove that long finned heatsink to gain access to the COF chip to lower-buffer-board connectors....

There's that long heatsink, so I think it's what you think it is. I'll remove it and check it, thanks.

[Alastair E]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

Aye--There's a Chip Mounted on the Mylar film that goes from the PCB to the glass of the panel--similar idea to LCD sets, but there's loads more of 'em all along the bottom!
When you remove the heatsink--You'll see the chip heatsinked to the chassis with compound and the long finned heatsink you removed. Often there's a silicone dead-toad pad between the removable heatsink and the chip on the Mylar, which is usually an oblong silvery thing on one side and a epoxy blob on the other. (COF = Chip On Film)

Its mad to think that a 1080p panel with its 1920 horizontal resolution has Three times that number of connections (5,760 different connections) to the chips from the glass of the panel, --each pixel comprised of the three primary colours

Its a huge shame--that if a chip fails on an otherwise great panel, its not replaceable and the whole panel is scrap. There are some models of Samsung--(D Series) that are very prone to this issue, Had one just recently, and another, where there was just one pixel vertical line of red that was stuck at full brightness!
Seems though--Every make has its models/ages that suffer with these things...

[Gof]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

Seems I might have some luck. There's a 10 ohm SMD resistor (R2 on the picture) that is broken (I measured it and it has a break).

By the way, it's on the power line to limit current spikes that would flow during switching Va because of capacitive character of the panel, right?

Anyway, I'll replace it, but it doesn't fix the second problem - snowing... do you have any idea about this snowing?

Thanks.

[tom66]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

I have had those resistors fail on an older panel without obvious cause, but it could also be because the COF chip under the black epoxy has failed. Is that a burn mark on the epoxy or is that just my imagination?

I think the resistor is involved in setting a current limit for the DC plasma discharge. Panel address is DC, but too low to cause significant light emission. A small current flows across the discharge gap during address. If this was not limited, then the ICs would have to conduct too much current. Sustain (AC discharge) does not need the resistor to limit the current, as the AC impedance of the panel does that...

[Alastair E]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

Ah--Forgot about those Resistors--Prob because in the cases Ive had--They were always OK!

Great--You got lucky. That picture has a little semi-circular line on IC2--Is that a hair or a crack in the epoxy of the chip?

As to the 'snow' Check all the panel voltages are right--Vs, Va, VSC, -Vy, VZ-Bias...

[Gof]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

It seems that this mark on IC2 is only a minor scratch. I'll be sure when I solder the new resistor (I ordered ten of them and I'm still waiting for them to arrive, I should have them on Tuesday). I'll put everything together then and then check all voltages (previously I've checked Vs and Va only).

[mmartell]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

Remember not to run the set without the heatsink in place.

[Gof]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

Remember not to run the set without the heatsink in place.

I know, thanks.

Well it seems I'm out of luck I replaced the resistor and it did not help. It seems it's like tom66 said that the COF has failed and just took the resistor with it.

There is a used panel available for about $60 on the local auction service (when a used plasma TV like this is available for about $200), I think I'll try to fix the snowing problem first (I'll check all the voltages) and then I'll buy this panel.

Thanks for help!

[Gof]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

So the situation now looks like this.

Vscw: should be 115V, was 118.4 ... 119.2V, adjusted.
Vy: should be -75V, was -73.6V on white screen and -76.8V on black screen, I didn't touch it.
Vsetup: should be 200V, was 194-196V, adjusted.

It did not help.

However - could you tell me if my Y waveform is correct? I found a service manual for this panel where it looks like setup1.png (attached), however measured waveform looks like setup2.png (attached). Basically, set_up hold time is 55us in my case, while it should be 20us, and there is a 20us period after voltage drops back from Vs+Vsetup to Vs and before set_down ramp starts (I can't see this period in the service manual). Set_down timing is correct (150us), but with this 20us Vs period it gives 170us.

Could this be the cause? I would adjust it, but this is so huge adjustment that I suspect that some component on the YSUS board is faulty... what do you think?

Edit: Nevermind, I measured wrong ramp (seems that there are multiple ramps on the Y signal)... so still nothing...

[Alastair E]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

Control-Board Firmware needs updating. You need special LG jig to do it with software and the appropriate firmware files.

[Gof]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

My first reaction was like "why would I need FW update when it worked and stopped?", but then I found this post and it explained it:

https://groups.google.com/forum/#!to...ir/BwxQni3q2U0

Quoting:

"Anyway, more importantly the display has a very common fault as in maldischarge (speckles) this is random all over the screen and noticeable mostly on black areas or light to dark transitions." (...) "I believe this is a very common fault caused by ageing of the panel, and LG supplied a firmware update for the control PCB to alter the timing of the sustain waveforms to compensate."

So if I order another (used, but working) panel, it is possible that the issue will be gone, right? As I need a new panel anyway (because the COF is broken in mine), well, there's only one way to be sure.

The panel should arrive around the end of the week, let's hope it will fix that.

[tom66]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

The problem with swapping panels is the control board will be out of sync with the panel. As the panel ages, the control board is supposed to update the drive waveforms to compensate, but the control board keeps track of this... it will "forget" this if a new panel is used... So the maldischarge fix may not work or it could produce undesired artefacts.

[Gof]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

The panel arrived and I swapped it. There are no artefacts, maybe I'm just lucky...

I've noticed two swollen caps (I didn't find them ealier) on the Y board - two 680uF/250V caps. I haven't noticed them ealier I ordered new ones, maybe it will fix the problem...

[tom66]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

They are not failed - common effect is as they heat up, the plastic protection domes can bulge, if you can press the dome down flat then the cap itself is OK.

[Gof]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

I unsoldered them (before reading this post) and it's exactly as you said.

As they're already unsoldered, I'll measure their capacitance and ESR and if they're OK, I'll solder them back (the ones I bought are for lower temperature range, 85°C, so if original ones are good, it would be better to solder them back, as they are rated 105°C).

Alastair E wrote about upgrading control board firmware. Can it be done without an expensive LG jig, for example using JTAG? There's an RS-232 service port, but it's on the main board, so I think it won't allow to download firmware to the control board...

Where can I find the firmware, by the way? Is it available somewhere?

Is there anything else I can check before being sure that the boards are OK and the firmware upgrade is needed to beat the maldischarge? Maybe diode check on the IPM on the Y-SUS and Z-SUS boards?

Thanks.

[Alastair E]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

The Control-Board is updated by plugging the jig directly onto the Cont Board, and using the 'flashdown' program to drive it from a PC--There's no alternative to update as far as I know.

The 'service port' on the set has no connection to the control-board, therefore cannot be used to update--OR LG would have used it!

As to swapping Cont Boards--Ive done it many times--BUT Always with updated F/W....

I can supply the F/W--But will need the exact Panel Number summit like 42V8####.

[Gof]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

Hi,

Panel model: there are two stickers with panel model, one says 42V6#### and the second one: PDP42V60000
Part number: 3315Q-E012A

Control board model: 42V6A
Partno printed directly on the PCB: 6870QCE016C
Partno printed on the sticker on the PCB: 6871QCH046C

EP1C3T100C8 FPGA has a sticker that says: 42V6AFPGA2 041223

How would you prefer to send me the FW? Do you want my email, an FTP or SFTP account or something like that?

Thank you!

[Gof]

Re: LG PDP RZ-42PX11 - snow on the dark picture (white is OK)

Oh, and there's one more thing.

On this board there are three different programmable memories.

1. EPCS1, which is a serial configuration device for EP1C3T100 FPGA chip. It has a sticker: 42V6AFPGA2 041223. Memory size: 128kB.

2. M29W320DT, which is a parallel flash memory, I believe it contains firmware run by the LGPCMv12H23 chip. Sticker: 42V6A3MN2D 041223. Memory size: 4MB.

3. AT89C2051 microcontroller. Sticker: 42V6T-01 041223. Memory size: 2kB.

Without a jig I will have to program them separately. All of them need reprogramming or just one of them (if only one will suffice - which one)? Does firmware contain three different files (or one file to be unpacked) for each of these memories?

By the way, when fiddling with the boards and disconnecting Y drivers (just to check - maybe without one of them the picture would be good?), I fried the bottom YDRV. I turned the TV on with YDRV_BTM disconnected from YSUS, but connected to YDRV_TOP and to the panel. And boom - I heared the crack. No visible marks, but when I plug it, Vscw disappears, so I believe there's a short there. I'll order a new one, but why did it broke? I thought that it is safe to turn on the TV with one of these boards disconnected. Maybe I should have disconnected it from YDRV_TOP before?