Toshiba TV Vertical Deflection Problem, Almost Fixed ?Need Ideas

The problem started with the picture being squeezed from both the top and bottom of the screen so that only the middle one-third of the screen had any picture information. It looked like an extreme version of letterbox format. Thwacking the side of the set would cause the picture to revert to normal size. After ten minutes or so it would go back to one-third size whereupon another tap on the side of the TV

the picture would stay normal sized. However, most of the time it would exhibit slight jittering, just enough to make the text crawl at the bottom of the screen a bit difficult to read. But sometimes the picture would lock in perfectly.

Eventually this extreme letterbox became a single bright horizontal line in the middle of the screen. I would take to warming the chassis of the TV using a blow dryer aimed through the back of the TV case. Thwack, blow dryer, thwack, blow dryer, etc. This is no way to watch TV.

newsgroup. This NG is a great resource. Thanks to all that post here.

There are a couple of electrolytic capacitors in the vertical deflection circuit that lose their integrity with age (heat cycling). The two capacitors mentioned are C305: 2.2 microfarad 50v, and C342: 1 microfarad 50v. I bought replacement capacitors from DigiKey-- Panasonic brand with 105C temp rating and 63v rating. Parts including shipping was $2.35. That sure beats the TV repair shop estimate of $140.00.

I avoided electrocuting myself and replaced the capacitors and also touched up the solder on the pins of the vertical IC and tested the TV. Upon initial power-up I had the familiar single horizontal line. Thwack on the side of the box. Full size picture. Crystal clear. Looking good. Then I notice there is a thin flickering horizontal line at the very top of the screen, but on only some channels. I also notice the score bar used to show information during football and baseball games and located near the top of the screen seems a bit lower than usual. It seems like the picture is not being stretched out

The set ran for about 5 hours one night and about 4 hours the next afternoon when I once again got the dreaded single bright horizontal line. Thwack. Picture is full sized again. Crystal clear. Single, thin horizontal static-ky line at the top of the screen. TV held the full sized picture until it was shut off for the night, about another 4 hours.

What other components should I suspect is causing this problem? Any ideas?

There is obviously a loose connection on a component in the vertical section, or leading to the vertical circuit. With the TV turned on and the back cover off, you need to gently poke around on the board with a non-metallic tool until you touch a component that causes the problem to go away. Or... with the TV off you should look at the solder joints with a high power magnifier until you find the suspect solder joints, and resolder those spots. If you keep heating and cooling the TV or whacking it on the side, eventually some of the components will fail completely. If the failure causes a bright enough horizontal line, it can burn into the CRT making a permanent line. You are on the right track but you must fix it right before more damage is done that you can not repair easily.

For now, I'd like to solve the thin horizontal line of static that happens at the very top of the screen. This seems to me to be a component that is on the hairy edge of failing--I don't think that poking it will cause the problem to go away--but I'm not certain. Anybody have any other ideas on why there is a line of static at the very top edge of the screen?

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I'm only guessing at this, but I think what you're seeing is not static but digital data. I see the same thing at the top of my TV picture (an HDTV signal converted to be visible on a regular analog TV). Normally this isn't seen because it's supposed to be above the viewing area of the picture itself. Closed-captioning and other information is embedded in the "vertical blanking interval," or the brief instant between frames of video.

That's what it sounds like.

He should check for a bad capacitor in the vertical output as well.

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Excellent theory, and I agree. This problem is most noticable on the local PBS station that broadcasts in HD. Also those channels that have the 16:9 digital signal seem to show this problem the most. Local analog stations don't have it.

Thanks to everyone for the suggestions. I'll look for the cap near the "jungle IC"--though it's usually not mentioned when discussing my model number TV-- and check out the low ohm resistor.

What you are seeing is line 21 which contains the closed caption data. Most sets overscan a bit and this should be off of the screen.

David

Look for a poor solder joint in the vertical output section. Tap around the inside with a non conductive thwacker where the vertical components are and be careful to avoid electrocution. Tap on the yoke too. Forget about the other issue until the vertical collapse is fixed.