Panasonic 50" VT20 arcing at edge of panel to frame

**budwich** · 03-06-2017, 11:02 AM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Originally posted by infrag

I cant measure to the dots or blobs or rivets as they are either encased in the glass or under the outside layer of the ribbon. I guess the ribbon I could take the outside off it but that kind of feels like danger territory for me. (as in dangerous to damage the TV)

I agree... my comment was base on the picture. I wouldn't disturb things unless there is complete failure condition.

**budwich** · 03-06-2017, 11:09 AM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Originally posted by infrag

There is 15V I believe thats meant to go to the A board.......

It start off at about 14.7-8 volts in Standby mode but goes up to 16V while on.
I've checked the voltage on the front of the screen again. When arcing the AC voltage does actually jump around but goes UP not down. The low level DC voltage i measured is actually a minus DC voltage or polarity reversed. Not sure if that helps.

that's likely because during the "arcing", sufficient potential has to occur to break down the "air gap" to cause the arc.... so it is likely quite high.... think "spark plug operation".... low current, high voltage.

**dick_barton** · 03-06-2017, 12:54 PM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Check your Y mains filter capacitor. It could be leaking to chassis.

**infrag** · 03-08-2017, 05:36 AM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Originally posted by dick_barton

Check your Y mains filter capacitor. It could be leaking to chassis.

OK fair call.
How do I test this and what Cap am I looking for?

Happy to post pictures of the psu if needed?

**aaronwt6** · 03-08-2017, 08:48 AM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

I've been following this out of curiosity. 20 years or so ago, a friend and I arrived at a customer's house to repair a C-Band satellite dish. We got quite a surprise when upon touching the dish, we got a nasty shock. It took forever to figure out where the voltage was coming from. Turns out, the person's TV had a defective capacitor (or at least that's what he was told later by the repair shop). It was feeding 200V or so to the chasis. The voltage was then traveling over the outter braid of the coax to the satellite receiver and then all the way out the coax to the dish.

Turns out, the voltage was also what had damaged the satellite dish. It caused a failure on the motor that rotated the dish itself.

**dick_barton** · 03-08-2017, 04:47 PM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Originally posted by infrag

OK fair call.
How do I test this and what Cap am I looking for?

Happy to post pictures of the psu if needed?

In the circuit attached they would be CY1, CY2, CY3 & CY4 all which connect to chassis so look for similar ones on your power supply board. I would remove and test.

Attached Files

darfon_b191-102_psu_sch.pdf (138.5 KB, 10 views)

**infrag** · 03-10-2017, 05:43 AM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Well to be honest the schematics give me a headache. I'd rather try to find them in circuit... Anyway I've had a look in the PSU for the caps going down to earth and found a few. I have 1 suspect which I've tested before but put back in as it seemed close enough.

Its a 230V 1000uf cap. It tests at 913uf. Initially looking at it seems fine but comparing to the other caps it has what seems like the begininnings of a bulge. Hard to say though. A resistance test returns 515kh reverse polarity and a jumping erratic reading the right polarity way.

Any advice on that or should i just wing it and get another one?

**dick_barton** · 03-10-2017, 09:30 AM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

The blue caps in the photo are probably the capacitors. Check if they are connected between the live or neutral input and chassis.

Attached Files

**infrag** · 03-10-2017, 06:04 PM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

OK one of the legs of each is connected to chassis. Then the other leg of one is connected to neutral and the other has its leg connected to live.

Not exactly sure how to test them but they test the same 0.30uf
Measuring resistance of them registers nothing.

**infrag** · 03-10-2017, 06:06 PM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Im guessing the other two blue caps are the other Y caps you were referring to. I'll check them out too if you think it worth it?

**dick_barton** · 03-10-2017, 06:11 PM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Out of curiosity have you used your meter to measure if there is a voltage between chassis and the frame where you believe it arcing to.

I wouldn't be bothered about the Y caps since they are across the mains so couldn't be leaking to chassis.

**infrag** · 03-10-2017, 06:38 PM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Yes. I did check that. However since I made sure the frame was sufficiently grounded to the chassis there is no voltage to measure.

**infrag** · 03-10-2017, 10:06 PM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

So in the picture attached I measure AC voltage between the strip indicated in red and the frame/chassis of the TV indicated in yellow. Does anyone else get this? I dont expect anyone to actively pull their TV's apart to check but I'd be very interested.

If you take the complete metal frame off the front and just measure between the strip and the chassis/frame of the TV does it make any difference for you?

Attached Files

**budwich** · 03-10-2017, 10:35 PM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Originally posted by infrag

Yes. I did check that. However since I made sure the frame was sufficiently grounded to the chassis there is no voltage to measure.

still trying to get my head around this.... so with statement, and the latest picture, are you seeing any more arcing in this "mode"?... assuming this statement means that the "chassis" and the now unmounted bezel are / were at the same ground potential. In one of your earlier posts, you placed a screw driver on the "chassis member" (I think ) and could cause a arc... is this true still / interpretation correct?

**infrag** · 03-10-2017, 11:45 PM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Originally posted by budwich

still trying to get my head around this.... so with statement, and the latest picture, are you seeing any more arcing in this "mode"?... assuming this statement means that the "chassis" and the now unmounted bezel are / were at the same ground potential. In one of your earlier posts, you placed a screw driver on the "chassis member" (I think ) and could cause a arc... is this true still / interpretation correct?

OK sorry for the confusing statements.

The screwdriver arcing was when I didnt have the metal bezel properly screwed to the frame. Therefore I could get arcing between the metal bezel and the frame with my screwdriver. Does that make more sense?

Since I have made sure its all fastened properly together while testing the frame and metal bezel is all at the same potential.

I can get arcing between the strip I've marked in red and the frame/bezel of the TV though with my screwdriver. Does that make sense too or have I just confused it more for you?

**budwich** · 03-11-2017, 11:09 AM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

ok thanks for the clarification.
but going from here, you then make this statement ... "However since I made sure the frame was sufficiently grounded to the chassis there is no voltage to measure". from this two questions, what did you do to achieve this? IF you back this out (ie. what you did), does your "screw driver test" still arc?

not sure it matters as I think I see that you indicated "1v" type reading before... which implies some small impedance difference between ground and the frame.

**infrag** · 03-12-2017, 08:04 AM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

OK I'll try to draw a usable diagram in paint tomorrow on a computer to explain what I did and where the arcing on the screwdriver was from.

As a side note can I test an A board from a 65" vt20a TV on a 50" vt20a TV and vice versa if the connecters are the same? I'm aware the backing plate might be different but I just want to test it if need be? (I picked up a 65" on Saturday night but it won't turn on with a 10blink code)

**infrag** · 03-12-2017, 07:55 PM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Attached is a badly drawn pain picture trying to explain the frame/screwdriver arcing I mentioned earlier in the thread.

Attached Files

**heavymachines** · 03-12-2017, 08:36 PM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Might need these, foam probably deteriorated inside just a guess what could be wrong ..... http://www.ebay.com/sch/i.html?_from...+foam&_sacat=0

**infrag** · 03-12-2017, 08:47 PM

Re: Panasonic 50" VT20 arcing at edge of panel to frame

Originally posted by heavymachines

Might need these, foam probably deteriorated inside just a guess what could be wrong ..... http://www.ebay.com/sch/i.html?_from...+foam&_sacat=0

I'll get some and try it.
The local component shop has:
Shielding Strip of Ni/Cu Layered Metallized Fiber/Polyether Urethane Foam with Tape.

That should do right?

Edit: Ordered a 1m strip. Cost $15 for 1m. If it make a difference I'll order more

Panasonic 50" VT20 arcing at edge of panel to frame

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