I have a panasonic plasma tv picture is fine when i turn it on but after a few minutes vertical line appear all the way across the screen. i checked the the main tv input menu and the lines do not go acoss it just the picture behind it. what could be wrong with it

If you wish to get some details; check the site linked here. Pull up older posts.
http://electronicshelponline.blogspot.com/
Line faults & possible causes to LCD & Plasma screen are given with illustrations. You can get an idea about the fault to an extent. Faults to all LCD & Plasma screen are similar, irrespective of its brand and screen size.

Fix Panasonic Plasma TV Vertical or Horizontal Bars ...

? 10:21
https://www.youtube.com/watch?v=CpWZTnAXbLg
Dec 30, 2013 - Uploaded by Pet Rock's Garage
This video covers how to fix a Panasonic 42" Plasma TV model TH-42PX600U that has vertical distorted ...

Horizontal black lines on Samsung 50" plasma tv - Forums - CNET ...

www.cnet.com > Forums > Samsung

CNETJun 11, 2015 - This past spring, a thin black horizontal line appeared across the screen, everything else is working fine. Next day ... In reply to: Horizontal black lineson Samsung 50" plasma tv .... I tried a white wash on the TV, but that didn't removethe line. Plasma TV has 3 thin black lines
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Black Line across Samsung 50" Plasma has appeared?
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Vertical black line on Sony PFM-50C1 Plasma Display
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If you wish to get some details; check the site linked here. Pull up older posts. Surf the site with patience. http://electronicshelponline.blogspot.com/
Line, faults & possible causes to LCD & Plasma screen are given with illustrations. You can get an idea about the fault to an extent.
LED blinking codes to Plasma TVs too is given.

Sound like your Y-Sustain board has one foot in the grave. The Y upper buffer and Y lower buffer boards go when the Y Sus Goes too...

The TV is a plasma screen. There are several circuit boards that will go bad over time that affects the picture quality. TV Parts Universal TV Stands DLP Chips ShopJimmy You can get the parts here and replace those boards yourself.

This is a Logic board problem, not so easy to replace in Hitachi but well worth the repair if I had your zip code I could recommend a person or three. But the problem is a problem in the logic board and will beed replacement, Thanks for using Fixya.com

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/edwy_1a56970cf1ea4620

The line of color is due to a failure in the vertical circuit. The main suspects are the vertical Ic AN15525A and/or capacitor c308 220uf@35volts
If you have the capacity to do so, you should check the other electrolytic capacitors in the vertical circuit which are USUALLY located near the vertical IC in most cases
you can purchase the part at
https://www.encompassparts.com/webwiz/wwiz.asp?wwizmstr=WEB.SEE&partnumber=5760279&smodel=CT32SL15N
or mcm electronics

put a towel across the top of the tv so it can heat up faster and you will get your picture. be carefull!!

Have you tried with a new scart or htm lead?

This sounds like one of the driver boards at the bottom or top of the screen has an intermittent fault. The set will have to be taken in to a service centre.