LG 42V7 Random Sparkles

[Engineersfoot]

Hello everyone,

I posted about this TV a while back and I discovered the original problem was a bad main board. After replacing it the tv started working great until it started giving me a new problem.

After around 30 minutes of use I get sparkles all over the TV screen after changing from a bright picture to a dark one. When the on screen display messages dissappear they leave a patch of sparkles where they where. From what I've read this is a classic problem with these LG plasmas.

The thing about this one is that the fault does not occurr when the back cover is off, ie it's heat related. When the fault is occurring the status LEDs on the TV change from 3 lit LEDs to only one. I can recreate the fault by blowing hot air down to the control board. Because of this I don't think the issue may be due to the y sustain but rather due to the control board. The training manual calls these LEDs "status" LEDs but it doesn't specify at all what they actually mean. Anyone on here know?

All voltages are dead on where they should be.

My question is, would a bad Y sustain board cause the status LEDs to change or are the status LEDs on the board only related to the control board itself? You guys think I should just wint it and change the control board? I don't want to risk changing a board only for it to turn out i got the wrong thing.

[Alastair E]

Re: LG 42V7 Random Sparkles

The set needs a Control-Board Firmware Update. Capkid in US can do it, as he's closest to you and so can I, but I'm in UK......

[Engineersfoot]

Re: LG 42V7 Random Sparkles

Hmm that kind of sucks.

Is there any way of updating the firmware without the use of the LG jig? Anything else I might be able to do?

How does the firmware affect the operation of this board and why does the fault end up being heat related? Would there be a way of solving this problem simply by supplying additional cooling?

[Alastair E]

Re: LG 42V7 Random Sparkles

Well--as a temporary fix you can try removing the heat-pad from the temp sensor and the bracket covering it on the corner of the control board. The 'status' LED's are temp indication.

Mal discharge is a known issue with LG sets, the timing/width of the negative spike on the positive ramp is extended to improve panel reset/cell discharge, prior to re-address...

(At least that's what appears the difference of before and after update that Ive noted)

A careful adjustment of SET_Up and SET_Dn can help, as well as replacing all the poxy surface-mount 33uF and 68uF caps on Y-SUS (Use 47uF and 100uF as replacements)--but ultimately only F/W update will cure it properly.

[capkid]

Re: LG 42V7 Random Sparkles

I got your PM. As I mentioned, I haven't successfully flashed a 42V7 board. I know that others have had issues with that revision, also.

[Alastair E]

Re: LG 42V7 Random Sparkles

One and only V7 Ive done did improve--but not completely cure the sparkles. I think that the V7 series is just so old now with many thousands of hours on 'em its luck of the draw. These early LG panels don't seem to last well IMO...

I certainly wouldn't waste any money on expensive parts etc for it!

Even when working well--They haven't got what could be called--A Brilliant Picture--being a 480 EDTV panel, although I did have a low hours Sony (Full of Nichicon Caps instead of the usual crap-cap that LG use) That version wasn't a bad picture--Except for its screen-burn....

Advice to O/P, 'Frig' the temp sensor so it works when hot and flog it fast Haha!

[Engineersfoot]

Re: LG 42V7 Random Sparkles

Hmm Okay, I'll give the temp sensor thing a try. I actually tried changing the thermal pad on that thinking it was a voltage regulator that was overheating. I guess the only voltage regulators are the fets.

The TV has sparkles from cold but they're not noticeable once you step a couple feet away, from what I read that can be considered normal.

[Engineersfoot]

Re: LG 42V7 Random Sparkles

Alright, tried removing the pads on the temp sensor. Still does it anyway. Temperature LEDs change. Is this sparkle problem normally related to the LEDs and temperature? I haven't seen too many people mention that along with the sparklng issue.

[Alastair E]

Re: LG 42V7 Random Sparkles

Normally it gets better as the set warms up--not worse, as the gas-pressure in the panel increases, ionisation becomes harder to achieve--due to the higher pressure.
--Thats why there's temp monitoring on the control-board to compensate.

For some reason--the panel becomes more sensitive as it ages, becoming more easy to ionise the gas, thus causing the issue.

Did you try the SET_Up/SET_Dn adjustments?--These can have drastic effects on the mal-discharge.

[Moreno83]

Re: LG 42V7 Random Sparkles

Did you try altering the small things on the mainboard/ysus/xsus? Sorry , don't know the name but this link shows what i mean! ( Im dutch :p )

youtube.com/watch?v=CkxpNpJZFyM

[Engineersfoot]

Re: LG 42V7 Random Sparkles

Hey, I haven't tried the Set Up/DN adjustments. Is that the one where you need to watch the wave form? If so I don't have an oscilliscope but perhaps I can get away with tweaking around and marking the original positions.

Any rough guides as to what I should do? Turn stuff up down or is it an experimentation thing?

[Moreno83]

Re: LG 42V7 Random Sparkles

The power supply is new right? Or is it 2nd hand?
I had the same problem with a LG plasma , it was really viscible in light colors like white/yellow.
I started to alternate first on the board on the leftside of the TV. You have to change the values clockwise ( slowly to the right ).
Your sending more voltage to those boards so be carefully and see if something is changing or not.

[Alastair E]

Re: LG 42V7 Random Sparkles

No! Shouldn't Randomly Adjust PSU board without monitoring the voltages--doing so, could end up in disaster by blowing summit up! (Been there, Done that Many times in the last 40 years!)

Check voltages by all means and set Properly with DVM/DMM

The SET_Up/Dn adjustments Should be done with a Scope--but when correct--with a scope--will still give the Mal-Discharge issue.

Careful alteration of first SET_Dn then SET_Up should help the issue, and Maybe then Reducing the Vs Voltage by 5V or so can help in some cases,--For this, you'll need a DVM/DMM The Correct Vs voltage is marked on the panel sticker somewhere around 180-200v.

Mark the pots with a pencil first to re-set to same spot if the adjustment fails to help.

--Dont twiddle anything else--as it wont help and can make for more problems!

[Engineersfoot]

Re: LG 42V7 Random Sparkles

Alright got it. Yeah I have a DMM and everything, I work on electronics just not plasmas and right now I don't have my oscilliscope. Power supply is original. Nothing wrong there. We'll see what happens.

[semiRocket]

Re: LG 42V7 Random Sparkles

Hello,

Just to be sure, is attached picture the case of what it's being talked about in this thread?

I have a LG 42PC3RA, after replacing IPM and a fuse on Z-sustain board, picture is great again, except this red pixel noise on black screen which becomes more noticeable when the set warms up. The noise is mostly noticeable in the up left corner and in the middle of the screen.