LG 50PN450B, first attempt :smoke, worth it trying again?

[senndogg]

Hello, its been a while since i havent been active in this forum, but now i am back in the business.
Here s the story:
A 2014 Lg 50" plasma recycling.
Disconnected the VS connector from the psu. The tv started without display, normally.
Inspected the zsus and found that 1 of 3 IGBTs at the SUS_UP was shorted.
Since i had no 30F133 available at the local stores i decided to give it a try with 2 transistors. No success, but then i find out that the 2 IGBTs of SUS_DN are shorted too. I fail to remember well if i measured them before or not.
Anyway i recover 2 identical IGBTs from another LG zsus and swap the 2 shorted. Measure everything, tight up all connectors, double check and ready for the test.
A visible arc goes between the chassis and the panel ribbon and the zsus goes popping soon after. IGBT of sus dn and up shorted again.
My question is, can this problem be panel related? I found a complete zsus for 40$ but im afraid to throw money into it.
Any opinions? thank you

[tom66]

Re: LG 50PN450B, first attempt :smoke, worth it trying again?

A visible arc goes between the chassis and the panel ribbon and the zsus goes popping soon after. IGBT of sus dn and up shorted again.

I don't believe this (not a criticism - just disbelief!)

Z-sustain output is max 210V, so arcing is pretty unlikely, unless the cables are damaged and close to the frame. Are you sure it arced?

The arcing may have killed the original Z-sustain.

Ensure all screws are secured to the board. Failure to do so may cause device failure.

It's really really rare for a panel failure to kill the Y or Z boards. I've never heard of it.

[goontron]

Re: LG 50PN450B, first attempt :smoke, worth it trying again?

^ I believe it. I've gotten 2mm arcs from 190v.

[tw2005]

Re: LG 50PN450B, first attempt :smoke, worth it trying again?

I've had arcing to rear of panel on a SS from a dried out split polyester cap. Did not kill anything except trigger a shutdown. Also had arcing across 2 points along the surface of a SC, dust build up.

Also it would appear looking at the power board the Zsus is tied to the Ysus. May pay to go over that too for shorts just in case the ZSUS damaged it when it failed.

I accidentally shorted a Z recently probing took out both boards.

[senndogg]

Re: LG 50PN450B, first attempt :smoke, worth it trying again?

Managed to find some similar IGBTs from salved pcbs. The arc is definitely there with a loud buzz. It is inside the chassis near the flex, i made an illustration.
Now it seems strange to me, why does it have to arc there, Z-out - GND is max 200V i guess. The gap between the 2 legs of the SUS_Dn transistor is 2mm, it can always arc there. Or maybe the flex is broken inside the glass and the PDP is gone forever.
Next thing, ill try an insulation between the flex and the chassis and see what happens. thank you for your time.

[Moreno83]

Re: LG 50PN450B, first attempt :smoke, worth it trying again?

Is that line on the flex originally there? Looks like a cut....

[tw2005]

Re: LG 50PN450B, first attempt :smoke, worth it trying again?

we had someone over here with a Panny with arcing around panel. I suggested the adhesive shielding that they have around the frames. Was a guess and a longshot but he ended up replacing that and reported it fixed. ??

[senndogg]

Re: LG 50PN450B, first attempt :smoke, worth it trying again?

The lower flex was isolated well with the rubber adhesive. To my surprise the upper flex started arcing with a loud buzz. Am i missing sth? Is this more complicated than just some IGBTs in the Zsus? Or the ICs which drive the IGBTs are also shot and they produce erratic behavior of the ZOut.
The reason while i am still asking for any clues is that i dont want to damage a working Zsus which i can find for 40$.

[heavymachines]

Re: LG 50PN450B, first attempt :smoke, worth it trying again?

we had someone over here with a Panny with arcing around panel. I suggested the adhesive shielding that they have around the frames. Was a guess and a longshot but he ended up replacing that and reported it fixed. ??

Yeah the what you called the most original fault you've ever seen. It was the shielding strips around front glass and it was fixed.

[senndogg]

Re: LG 50PN450B, first attempt :smoke, worth it trying again?

thank you for your time and efforts guys. Sadly i ran out of ideas so handed the faulty tv to the owner.
It is still a mystery to me why it arced like it was working on thousands of volts, no kind of insulation could handle it. The display on those tenths of sec showed an erratic grey screen like a no signal tv tuner.
Anyway, i have to study again because plasmas are still a dark spot in my electronics knowledge. You can recomend me some literature.
Thanks again.