Horizontal linearity problem - Vestel 11AK49 chassis

ProDave · Joined: 06 Mar 2007 Posts: 13

I have a JVC 28" WS television that has a Samsung tube and a Vestel 11AK49 chassis. I have the service manual for the chassis.

I have worked theough the setup parameters in the service menu and now got this set working pretty well, but still have one slight problem.

The horizontal linearity is slightly out. The left hand end of the screen is slightly too bunched up, and the right hand end of the screen is slightly stretched out.

Trouble is I can't find any parameters in the service menu that deal with horizontal linearity. There's all the usual vertical linearity and trapezoid / parabola adjustments, but all there is for horizontal is width and shift. Or is the parameter that I want one of the ones with an obscure name and no description?

So how do I correct this slight horizontal linearity problem? or is it a "feature" of the tube that i'm stuck with.

The set is 6 months old, so unlikely to be a component failure.

Guest · Posted: Fri Jan 04, 2008 9:16 pm Post subject:

Hi mate i found that the trapiz settiing in sevice mode works liniarity on one i had hope it works for you Bob

torbjorn · Joined: 07 Jun 2007 Posts: 370 Location: Sweden

Do you know if other identical televisions have similar linearity problems? It is fairly common that a television chassis which is being used in sets of many different brands with different tubes and deflection coils, shows bad horizontal linearity together with some of them.

There is almost always a linearity coil, i.e. a coil where the core is saturated by a permanent magnet, in series with the horizontal deflection coils. In old days, this one was adjustable but today almost all of them are fixed. This linearity coil, together with perhaps some RC networks, must be properly matched to the deflection coil to give good linearity.
One possible fault could be if the linearity coil is connected with the wrong polarity (so that the core gets unsaturated at the wrong half of the horizontal scan). Try reversing it and see if the linearity gets better!
Also, check out the schematic and parts list to see if the correct parts for this particular tube are fitted.