Increase or Decrease the resistance of a yoke

[robmoto]

Hi
I changed the chassis of my monitor by a chinese standard one , and the width of my picture is too large.
I didn't knew about the chassis compatibility with the yoke resistance and that could change the image size

The chassis is:



Compatibility yoke
V = 11.8 Ohms 12.70mH
H = 2.14 Ohms  5.27mH

 and my monitor has :
Vertical coil = 8.3 Ohms
Horizontal coil = 4.8 Ohms
I can't measure inductance sorry.
So the vertical coil is too low by 50% and the horizontal coil too high  by 100%

If I add a coil from an external transformer like this in parallel of the horizontal coil. 4.8Ohms / 1.6mH



and a serial resistor 3.9Ohms after the vertical coil by doing this:


 it will match the chassis compatibility.
Is it correct or it won't work ? 

Thanks 

[buttersoft]

I'm genuinely interested to hear expert answers on this, and the reasoning behind them.

My gut says you can sort of do what you suggest to the vertical section, there's probably a resistor across the coil/s anyway, but the horizontal deflection can't be played with. Even if it worked electrically, the linearity would go out the window, and probably the convergence too, like when one of the horizontal coils of the yoke breaks but not that bad. It might simply release the magic smoke and give up quicker than you can find out though, IDK.

[Arroyo]

Those resistance readings on your yolk are probably within the range of tolerance.  Only way to know for sure would be to talk to the manufacturer of the chassis.  Having said that the more accurate measure is inductance as it’s what really matters.  Resistance is an inaccurate approximation.

Your problem could most likely be solved by adjusting the horizontal width coil.  If you look at your chassis schematics or other documentation you should be able to find it.

IMPORTANT: they are notoriously fragile and you DO NOT want to use a metal screw driver to turn it.  There are plastic screw drivers that you can use to adjust it gently enough to not damage it.  They become more brittle with age, so if yours is newer then it should be sturdier.

[jennifer]

I would have to be of the opinion... The transformer would alter inductance, and most likely make things worse, The math on that is crazy deep and beyond my self taught education, It would probibally be easier to just replace the yoke. https://archive.org/details/MITRadiationLaboratorySeries22CathodeRayTubesDisplays/page/n3/mode/2up

[grantspain]

hantarex do this on the mtc9110 so it matches a 25" yoke
imo you would be better off getting a chassis that matches your yoke

[robmoto]

Hi ,
ok i have heard your advice and looked for another solution .

But did you know about "Trafo Yoke" from Wansonic ? it seems to be an external transformer with multiple coils that you can add to adjust the load of your Yoke?



Finally I have found another way on my chassis , i lowered this Resistor before VPOS trimmer from 1500 to 360 Ohm ,so i can adjust correctly my image Position vertically.



and i moved the Red wire from right to left pin (didn't knew this !  )  the image is not so wide now.