TV shows only about a one inch wide horizontal strip in middle of screen, the rest is black. It actually looks like it is showing what is supposed to be at the very bottom of the screen but is perfectly centered. It started out only doing this occassionally, but now that is all it shows. Why? How much would it be to fix?

It is line fault. Contact any service technician. 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 screen are given with illustrations. You can get an idea about the fault to an extent.

Generally this is not good news. Even in the event this TV is repaired, it will work very long. This TV has a horizontal problem. This is the most stressed area of any conventional TV. The Horizontal Output Transistor will need replace, the flyback transformer is bad, you have bad power supply with horizontal capacitors that are bad, and last, is a possible bad picture tube. This TV is not worth the effort or money to repair. Thanks for asking and show all hands of support!

i think your vertical IC ( if vertical lines are shown) / horizontal IC ( if horizontal lines are shown) of your monitor has damaged. you may contact a mechanic and change the corresponding IC

The line is there because the vertical deflection unit - the one that spreads that line across the entire screen to form the image - has failed. Replacing it is a job for a professional, or at least an experienced amateur, and the parts will be quite difficult to find for such an old tv . 

There is no invertor board on a plasma tv. The fault is the X address buffer board. This is located on the bottom of the screen and runs horizontally the whole width of the screen. If you remove the heatsink plate that covers the x address boards and you need to look at the screen ribbon at the same position as where the bar is (in the middle).Vary gently lift the Xbuffer ribbon lock and gently take out the ribbon.Clean the contacts very carefully with a fibre pen or an electrical cleaning fluid.Insert ribbon back and heatsink and check.Here is a picture of the board and ribbon


a 1 inch bar is associates with 1 ribbon fault. So if the bar was 3 inches in from the left of the screen, the faulty ribbon will be 3 inches in from the right working from behind the TV. If cleaning dont cure the fault, then the Buffer IC will be blown and order a new centre buffer board (you can buy off Ebay)

You will need to replace the Horizontal IC around $80 bucks for the parts and labor. What happen here is when the Horzontal ic gives out the screen basically folds to the middle. Do not shoot the messanger here but have the TV looked at by a professional locally.

I hope this was Very Helpful to you today please leave your feedback and ratings.

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

Horizontal centering is performed in the service menu. Beware! You can mess up a lot of stuff in this menu.

Just to be sure that I send you in the correct direction, does this strip look like a shrunken picture with no height? In other words is it a horizontal bar?

Thanks,
Dan

This is a problem with the LCD panel. If the tv is out of warranty, I would call Samsung and see if they will pay for the panel and you pay for the labor. The panel is not cost effective to repair. If Samsung will not do anything you will need to buy a new tv.

check for bad c14505 220mf.
or u14501 vertical output ic.