Warped CRT TV fix?

[aaaaaaaaaaaaaaaaaaaa]

So I found this CRT TV on the side of the road. It works ok, but the picture is warped; you can see in the attached photo (don't mind the monitor wave from the camera) I have an old computer hooked up to it and the raster lines at the top of the screen appear vertically stretched, distorting the image and clipping the top portion. Now I don't know much about analog TV (other than the basic theory of using basically some coils to move the beam and draw the raster image at 60 hz ntsc blah blah). Don't ask me how a colorburst signal generator circuit works cause for all I know, there's just a bunch of tiny elves running around inside the ICs making it all work. However, I do have some basic electronics equipment for soldering/desoldering (and some experience soldering/desoldering as well) and also some parts like resistors, caps, diodes etc. I just need to figure out what has caused the warping and how to fix it safely (if even possible). Could it be as simple as tuning a trimpot somewhere in there?

 

[tvtech]

Hi

Normally that's caused by electrolytic caps in the vertical stage that have gone low in value which affects the pictures linearity.

Check vertical stage caps with a cap tester.

 

[ramondo]

I would suspect a horiz blanking problem or a possible yoke misalignment. Look for anything loose or moved on the neck of crt.

 

[tvtech]

I would suspect a horiz blanking problem or a possible yoke misalignment. Look for anything loose or moved on the neck of crt.

No...you can clearly see the vertical linearity is out. Please check the vertical stage electrolytics and replace any that are low in value. There are not many caps to check - max of 5 or less there.

 

[aaaaaaaaaaaaaaaaaaaa]

Ok thanks for the quick replies guys. Unfortunately, I don't have a meter that can measure caps but if there's only a few that could be causing the problem I mean, hell I've got some electorlyics lying around, I'll have to check it out but perhaps I'll just find that part of the circuit and replace em. I'll open it up and poke around and report back.

 

[ramondo]

My Bad,, I thought OP was viewing on a monitor with known vert lin problems.. I should read slower.

 

[Nigel Goodwin]

No...you can clearly see the vertical linearity is out. Please check the vertical stage electrolytics and replace any that are low in value. There are not many caps to check - max of 5 or less there.

I would have thought probably only three? (although I've not done CRT for a good few years now).

In order of likelyhood:

1) Output capacitor.

2) Bootstrap capacitor.

3) Frame supply reservoir capacitor.

At least with CRT you've got some hope of repairing it