Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

[Alastair E]

I finally found a good Mainboard for this set.

Originally, the set would initialise the panel, and have a very dim glow, but no picture whatsoever, no matter what you did, no menus or OSD

Fitted this Mainboard, and I thought all was well--For a half-hour or so.

Then, it went dim and pinkish for a couple of seconds, (SS int. failure?) then back to normal.

I tried to provoke the set to do this again, but no amount of tapping or anything else would make it fault. It happens at no particular picture content and is completely random.
Sometimes, the set will run for an hour before doing it....

Since then, the set will do the same thing randomly, once just after turn-on when everything was stone cold, so I don't think its temp related.

Its not logging any fault-codes and no shut-downs or blink-errors.... The LED's on both SC and SS stay lit.

V-SUS remains exactly the same, (188V) during fault....

[tom66]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Hmm. My first guess would be a cold joint on the SS board.

Have you checked Ve voltage - is it steady? Check pot is clean.

Loss of Ve would cause pink & dim image but I think no fault detect would fire as there's no way for it to know the state of that supply unlike SC board which can 7 blink for vad/vscn failure...

[Alastair E]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Hi Tom!

Would you believe it, I'm monitoring the Ve currently, and the set hasn't faulted since....

I did twiddle the pot and return to its original setting--the set however faulted after that but since monitoring Ve, --It hasnt.

Cant see any dry-joints and no matter how much I tap, pry, distort or any other abuse to any board, the set continues working....
--Hate this sort of fault.......

[Alastair E]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

It Just did the fault....

Ve increased to 145 from its normal 131.....

When the fault cleared, I adjusted the pot to increase the Ve again to 145 to see the effect.

There was no apparent affect on the picture. I then set back to 130v....

This gives me the impression that the Ve supply during fault condition is unloaded and climbing a little due to no-load.....
--Just need to see where/ what that Ve is supplying now....

[tom66]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Could be a sign that the Ve ckt is not being loaded, in other words the Ve driver is not working during that instantaneous moment. Think it's time to get a scope on it...

[ERICSSON89]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Ve voltage? what is it and where is it located on the set, what function did it perform please? still new to the forum. any answer would be appreciated.

[tom66]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Ve voltage? what is it and where is it located on the set, what function did it perform please? still new to the forum. any answer would be appreciated.

SS board common electrode initialisation voltage...

That's a mouthful but basically it's a voltage generated on the SS board which is important during the erase and initialisation ("priming") portions of the display drive.

If Ve goes too LOW: picture goes dim, pink or black splodges appear.
If Ve goes too HIGH: picture blows out, extremely bright, no low level detail, TV may shut down from Vs over-current.

Called Vzbias on LG plasmas...

[Alastair E]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Hmm--Only thing that the main bulk of Ve current would go through that I can see, is Q339, which is a small SM MOSFET. Its Source terminal is at Ve and the Drain is the panel-tabs.....

Hmm--Think I'll change it anyway.

I have an SS board from a 37" PX80B thats Near identical--Except the sockets for the screen-tabs are too close together, dont line up with the 42" panel tabs--Even contemplated changing the position of the tab-plugs--to the Outer set of holes provided.....

Trouble is, the thing faults so infrequently, this repair is gonna take some time--Apart from running the thing for hours, you'll never know if its fixed or not!......

Seems Pan have the monopoly on Intermittent Faults, Just got shot of a PX70B with int. 7 blink (Gave up on that,--wasted days on it-- changed the SC in the end).....

[ERICSSON89]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

thanks for the feedback TOM66. I get that clear now.

[tom66]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

You can try this trick. If one tab lines up, run the panel with only one tab.
It'll be no good with EMI, but the tabs are internally connected - at least, on the PZ80's... so it should run.
You MAY have to disable the 8 blink SOS by grounding one of the cathodes... can't remember now.

[Alastair E]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Well--It aint the MOSFET, Q339 Shortly after replacement, it faulted, corrected and faulted twice more....

As the 37" also needs a Mainboard And PSU work, I think I'll break out the hot-air and switch over the tab-sockets, and bung its MOSFET back on, that I robbed off it.....

[Alastair E]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Well, got the tab-plugs changed over, MOSFET re-fitted,

Still the bloody same--with the replacement 37" SS board.....

[tom66]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Hmm, could be a problem with the D board... or perhaps even less likely, the SC board.
Any chance you could use the 37" D board in the 42"? Resolution is wrong, but this should only cut off a tiny bit of the bottom... should be ok for a quick test.

[Alastair E]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Oh dear.....

No 'D' Board, Its part of the Mainboard......

The 37" Mainboard--Is Faulty Too! Doesn't even initialise panel....

[tom66]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Yuck...

Best I can suggest is to hook a scope on to it, preferably a digital one if possible - set it up for a segmented capture every 1/2 second. My Rigol will do 5000 saved captures onto RAM, so you can play back through the best part of an hour in 10 seconds and see what's going wonky.

If that's not available you'll just have to watch a CRO until it does go bad... hope that a change in the waveform will be obvious...

[Alastair E]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Well All I have is a modified Tektronix 2445, (Now up to 2465 400MHz spec, Great scope, best bit--It only cost me a fiver)

I'll hitch it up to the various inputs that drive the SS and see if one drops out. All I can think of at this point.....

[Alastair E]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

So, Monitoring the drive signals to the SS board, I lose the signal completely at pin 7 of SS23 during the fault.

Pin 7 is called, UML (Whatever THAT means....)

[tom66]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Lower IGBT drive on SS board..
I suspect you've got an int. fault on the "D" part of your A board...

Could be intermittent connection on the C board.. signal passes thru there.

[tom66]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Maybe try hitting IC17203 with a bit of freeze spray - it's IC203 on the C2 board - it's a buffer for the signals for SS board, perhaps intermittent?
Also check UML input on that. Schematic available on Elektrotanya...

[Alastair E]

Re: Pan. TH-42PX80B Intermittent Dark, Pinkish picture.

Thanks Tom,

Ive been using the manual--Think I got from your site, and saw the buffer on the C2, --as is usual, its buried under stuff, was trying to plot through the (Horrible) diagrams as to where it comes from on the D part of the A board, and hoped to pick it up there....

I can now confirm, all the other drive signals to the SS from pins 6 to 11 except pin 7 are OK and do not vary much except to picture-content and then not much...

Job for tomorrow I think, I just cant cope with that Orrible schematic much more tonight....