In yet another TV problem question: I have a Zenith 25" television that’s about 12 years old. Lately the picture has begun to go all wonky. There’s a black horizontal strip at the bottom where the picture is starting to pull up from the bottom. The lower third of the picture is squeezed so that everyone appears to have really short legs. The top third of the picture is slightly stretched giving everyone one of those This Island Earth alien foreheads. Even though I plan on replacing the set soon, I’d like to know what’s causing this and if it could be cheaply repaired so that I could donate it to Goodwill.
Well, if you feel like opening it up, there’s two controls that might help. One is probably labelled Vert. Lin. for vertical linearity. This contols the linearity or “evenness” of the vertical scan cycle. The other is the vertical height (this one is usually accessible from the back on older TVs). Of course these adjustments must be made with the set on, and you MUST be extremely careful. If you’re unfamiliar with high-voltage safety, don’t try it.
I had the same problem a while back. I took it to a repair shop and it only cost around $60. Granted, $60 isn’t chump change, but it beats having to buy a new TV.
A television works, quite simply stated, by shooting a beam of electrons at the screen from the inside. When that beam hits the screen, it makes tiny dots glow… you can see these individual dots if you look closely enough. The beam hits each individual dot, in turn, over and over again, so fast that you can’t tell it’s doing it. Just looks like the picture is moving.
The way it picks out each dot is with magnets. There are tiny magnets near the cathode (Part of the Cathode Ray Tube, which shoots the electrons). The TV or monitor uses the signal it’s given to very rapidly change the strength of the magnets, which ‘bends’ the beam of electrons into just the right spot. This is a very precise type of thing, it has to be to hit exactly the right dot so frequently.
The Vert. Lin. adjuster is just a little dial, deep inside. It is one of the ‘ways’ to tell the beams where to go.
If your magnets are off a little bit, maybe the set got bumped or something, you’ll have to re-adjust the system to compensate.
I will emphasize what QED said… do NOT try this yourself, if you aren’t familiar with electronics. The inside of a television, even unplugged for 20 years, has things that can KILL you if you touch them. Leave it to someone who knows what those things are.
Now for my WAG: You have some large speakers placed near the screen. Perhaps you hooked the stereo up to the cable or something.
MOVE THEM!
Magnets are VERY BAD for CRT’s!!!
Nope, it’s been sitting in the same place for the last seven years and there’s not a magnet anywhere near. It just started doing this in the past 3-4 weeks.
When electronics sit unused for a long time, some parts can degrade, most noticeably, electolytic capacitors wich are infamous for developing “holes” in the oxide layers on the plates, due to the electrolyte between them partially crystalizing, and losing their capacity. This can and will skew the delicate alignment of all the various circuits that make up the televison set. In some cases, using the device again for an extended period will “reform” the caps and bring them back towards spec, but adjustment is almost always necessary to realign everything.