LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge

[sean0118]

Hi Everyone,

I saved this plasma from the side of the road because I thought it was a Panasonic, after getting it home and reading the label again I realised its a Palasonic. I think Palasonic is local to Australia, but its just a rebadged LG PDP42V7.

It has quite a bit of maldischarge when transitioning from a light to dark image. I know this is only a standard definition Plasma and is basically worthless, but still would like to get it working. Otherwise I'll part out the boards for spares.

I tweaked some of the voltage rails because they were a bit out, currently they are:

Vs = 186.8V
Va = 65.1V
Vy = -80.4V
Vsc = -120
Zbias = +165

The low frequency ripple on Vs is ~2Vpp (and about 10Vpp high frequency spikes, but I think that's measurement error).

The large purple capacitors on the y-sus board it warm (~45C), but I don't have any suitable replacments on hand for them.

There was another electrolytic on the y-sus which was also ~45C (hotter than the heat sinks around it), it's the one with the red arrow pointing to it. I replaced it with a spare I hard, doesn't get as hot now but the picture is unchanged.

I've also attached some waveforms of the y-sus and z-sus. The y-sus looks quite different to pg. 14 of the manual (attached).


Any ideas where to go next?

edit: also, I've resoldered the coils on the y-sus board, no change though.

[R_J]

Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge

try adjusting the set_up & set_dn slightly (mark their original setting) other than that this does look like the models that required the control boards to be updated.
Or just panel age

[sean0118]

Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge

oh, yes I should have mentioned, I have tweaked set_up and set_down to try and get the y-sus to match the waveform in the manual.

set_down is longer than it should be, it's something like 120us instead of 100us. But if I reduce set_down it just makes the ramp reach -Vy earlier then it stays flat at -Vy, it doesn't go back up to 0V earlier. Does that make sense? Otherwise I'll save a scope image of it.


edit: What sort of programmer is used to update the firmware? I saw this mentioned in another thread for the LG PDP42V7.

[sean0118]

Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge

I reduced set_down a bit so the down ramp is 100uS. The quick reference book (attached) had some waveforms which were clearer than the manual.

I also tried varying set_up and set_down as well as Vs. Did see some changes, but didn't fix it. If I decrease set_up a lot I get dark sparkles instead of bright ones.


Anyway, I noticed there's 3-4 Samwha RD capacitors (10uF, 350V) on the Y-sus which heatup a lot. Some are over 45C, hotter than everything else on the board, including the larger purple Samwha filter caps.

So I might try and find some replacements for those and see what happens.

[R_J]

Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge

You can also try changing the Vs slightly, sometimes lowering it by around 5 volts can help, I don't know where to get the control board programmer, and you would also need the latest firmware, it may not be available anymore. this is an old tv.
The scope is the best way to adjust the setup/setdown but as the panel ages its best to adjust it for best picture.

[sean0118]

Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge

Thanks, I haven't tried lowering Vs that much, I'll give it a go.

I'll try to adjust setup/setdown some more too.

[sean0118]

Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge

It was worth a try, but lowering Vs didn't improve it. I think I might have gotten it a bit better with some small adjustments to set_up and set_down. But it's still maldischarging.

I ordered some replacement capacitors, I'm not too hopeful but curious to see if it helps.

[sean0118]

Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge

I replaced all the Samwha RD capacitors (10uF, 350V) on both the y-sus and z-sus. But can't see any change.

One thing I did notice is the maldischarge gets worse the longer its left on. I tried to reproduce it with a heat gun but couldn't. But If I leave it on a white screen for ~15min it gets quite bad once I switch back to a normal image.

Does this model of LG have an 18V rail for the IPMs? Where is it best to measure it?

[sean0118]

Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge

Nvm it's a 15V rail and the best place to measure it is B21 at the bottom of the Z-sus. Mine was ~15.2V so seems fine.

I'm out of ideas again. I guess it could be the panel, but seem strange that it gets worse the longer its on.

[sean0118]

Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge

Are these oscillations normal for plasmas? I can see them on both the YSUS and ZSUS waveforms.


edit: Uploaded second image, yellow is YSUS, blue is ZSUS.

[angelos]

Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge

Hi Sean,
I will give you a heads up. I have a brand new PDP42V7 (purchased from Game, same as Walmart as salvage) whose plasma was cracked. I had removed all the panels and bubble wrapped them. I then got a repair in that was making a lot of sparkles (mal-discharge) so i had all new boards. I swapped out all the boards with new ones and upon switch on the set was perfect but after a few minutes those sparkles started again. I then assumed it must be panel.
The only boards i did not replace are the buffers at the bottom of the screen.
Hope this helps you.

[sean0118]

Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge

Thanks Angelos, I think you might be right and that my problem is the panel.

I found quite a few documents from LG saying that the firmware update and different voltages are required to fix it. But none of the documents I have list the new voltages.

I decided updating the firmware was too much work, even though it might be possible with a generic programmer.

In the end I set my voltages to those in the 'Quick Reference Alignment Hand Book' (Va = 65V, Vs = 188V, -Vy = -75V, Vsc = 115V, Zbias = 165V).

But I reduced Vs to about 183V. I then tweaked Setup and Setdown a bit, but not much from the 10us/100us in the guide.

I did find that in my case the maldischarge got worse the longer the TV was one and the IPM on the YSUS was getting quite warm (~55C). So I attached a fan on the inside of the back cover to draw air in near the YSUS. This was soldered onto the +5V connector pins of the YSUS.

All in all, I think it's improved a bit, but there's still a fair bit of discharged on some dark colours. But it's good enough, I'll call this a success.


I probably shouldn't upload them, but the titles of some useful documents are:

1. SVC Application Guide PDP TV-H2 series, fitted with 42V7 Module
2. LG_Plasma_Training XCUTE 125
3. LG PDP Module Service Manual Model: PDP42V7#### 2005
4. Philips LGE PDP 2K5 Service Manual 2007