TV image jitters - please help (1 Viewer)

[varon]

Hello,

Why changes in picture intensity or content cause my picture
on my CRT TV expand (vertically) back and forth, depending
on the amount of brightness.

What is the cause ?
What needs to be done to fix this phenomenon ?
Is it a calibration issue ?

Thank you,

-Avi.

 

[Kirk Gunn]

Varon - I do not have any recommendations, but it will help others to know exactly what make and model TV you have. There are a lot of qualified people browsing this forum (ISF Techs), but you've got to throw them a bone !

My only comment would be to try another AC outlet, could it be that the circuit is reaching it's maximum rating ? (Pulling at straws...)

Good Luck !

 

[varon]

The Model is Sony KV-36FS70K (I believe it is the PAL version of the XBR)

There is no chance the outlet is draining out, it is 220V/16A !

Can this problem relate to the fact that the picture is distorted
(hour glass) ?

Thanks,

-Avi.

 

[Allan Jayne]

On lots of TV sets (CRT based) the picture expands slightly during brighter scenes and shrinks slightly during darker scenes. This is due to less than perfect internal voltage regulation and sensitivity of the electron beam deflection circuits to these voltage changes.
If the expansion and shrinking is profound, that may suggest that some of the components are degenerating or have failed. Some sets use a "bridge rectifier" consisting of four diodes arranged in a square where if one of them burns out the capacity of that part of the TV power supply circuits is cut in half. If the power supply cannot deliver the needed current, the voltage will drop as other circuits attempt to draw more current (which happens during bright scenes). The voltage may vary fast enough so if the middle of the screen has dark subject matter, just that portion of the picture will be narrower giving an hourglass appearance.
You can try turning off large appliances (not the fridge or deep freeze) and see if that helps but more likely it is the power supply circuits inside the TV, not the electrical outlet.
Video hints:
http://members.aol.com/ajaynejr/video.htm

 

[varon]

Thank you Allam,

This problem appeared only recently, so which component should be
checked/replaced by the lab in order to restore the factory quality ?

-Avi.