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Clive Tobin · Guest

Back in Ye Olde Tymes the tube sets used to have Width slug-adjusting
coils, as well as pots for Height.

New stuff seems to have no adjustments whatever for Width, and only for
Height if you are lucky.

I would like to be able to eliminate overscan on some monitors, to see
the whole video signal. I have one supposedly Underscan-capable monitor
that still does not show the corners of the raster. Underscan monitors
are harder to come by and expensive. The last couple I bought on Ebay
went up in smoke just after putting them in service.

One approach I tried was to use a video to VGA scan converter, with a
computer monitor, all of which seem to be adjustable to underscan.
However, the one I tried (Super Joymate??) leaves out about 1/2" of the
right-hand side of the picture, compared to a true underscan video
monitor.

What part does the factory select to adjust the width? Can you stick a
coil or resistor in series with the yoke winding to reduce the width?
Will any of this mess up the geometry, disturb the high voltage, or
result in a frantic call to the fire department? Thanks. (Previously
posted in sci.electronics.design)

NSM · Guest

"Clive Tobin" <clive@webband.com> wrote in message
news:1105300176.120959.179030@c13g2000cwb.googlegroups.com...
| Back in Ye Olde Tymes the tube sets used to have Width slug-adjusting
| coils, as well as pots for Height.
|
| New stuff seems to have no adjustments whatever for Width, and only for
| Height if you are lucky.
|
| I would like to be able to eliminate overscan on some monitors, to see
| the whole video signal. I have one supposedly Underscan-capable monitor
| that still does not show the corners of the raster. Underscan monitors
| are harder to come by and expensive. The last couple I bought on Ebay
| went up in smoke just after putting them in service.
|
| One approach I tried was to use a video to VGA scan converter, with a
| computer monitor, all of which seem to be adjustable to underscan.
| However, the one I tried (Super Joymate??) leaves out about 1/2" of the
| right-hand side of the picture, compared to a true underscan video
| monitor.
|
| What part does the factory select to adjust the width? Can you stick a
| coil or resistor in series with the yoke winding to reduce the width?
| Will any of this mess up the geometry, disturb the high voltage, or
| result in a frantic call to the fire department? Thanks. (Previously
| posted in sci.electronics.design)

This is not for the unskilled, but a square turn of copper can be shimmed
under the yoke to reduce width. Must be flexible of course.

N

James Sweet · Guest

"Clive Tobin" <clive@webband.com> wrote in message
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Phil Bowser · Guest

I don't recommend the resistor trick...I was bored one day last year and
played with this idea on a 20" RCA TV...yes a 1 ohm resistor in series with
the vertical yoke will reduce vertical size, but it had to be
enormous...over 20 watts to do the job without smoking... The inductive load
of the yoke - yes even the vertical... carries enormous current levels and
will give that resistor a real enema by dissipating most of the power of the
circuit in IT.

James Sweet · Guest

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NSM · Guest

"James Sweet" <jamessweet@hotmail.com> wrote in message
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| Hmm how about a capacitor? I was thinking it was a resistor but perhaps I
| was wrong, I saw it in an old 1970's book about computer projects.

A capacitor that's larger than the monitor? What will that cost?

N

Andy · Guest

The line output is a tuned circuit, lowering the value of the capacitor will
alter the width.Look for a cap with a value 2nf t0 10nf ,and a working
voltage of 1500 volts or above.
"Clive Tobin" <clive@webband.com> wrote in message
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James Sweet · Guest

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NSM · Guest

"James Sweet" <jamessweet@hotmail.com> wrote in message
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| For the vertical circuit? Seems like I've seen non-polar lytics in series
| with the vertical yoke before but maybe I'm remembering wrong. At any rate
| vertical is fairly safe to screw with, the horizontal is much more
critical.
| Suggest finding a datasheet for the vertical output IC and look into
| reducing the scan.

I'm guessing that for the current involved it's not going to be a tiny cap.

N

James Sweet · Guest

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NSM · Guest

"James Sweet" <jamessweet@hotmail.com> wrote in message
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| How much current could possibly be involved? Typical Vcc for the vertical
| circuit is 24-40v, it's usually supplied through a 0.1 ohm or so fusible
| resistor, can't possibly be more than an amp or so.

But how much impedance do you want to add?

N

James Sweet · Guest

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NSM · Guest

"James Sweet" <jamessweet@hotmail.com> wrote in message
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| Dunno, most vertical yokes are 30-50 ohms, 2-3 ohms should be plenty to
drop
| the height a bit.
|
| Perhaps this is the wrong approach though, better might be to trace the
| circuit of the vertical size adjustment, perhaps you can add a resistor in
| series with the pot.

I'd be looking at the vertical drive to see if you could control that.

N

we · Guest

The "New" TV's have service menus reached thru the remote control.
There one will find horz./Vert. size and positions
Get a service manual.
Matshuta's and Sanyo's of at least 5 years or so have it.

Now short of menu driven size adj. a company called "VideoTek" used to
"Jeep" old Sony's and such for video inputs, pulse cross and underscan with
blue gun only. Because color monitors 15 years ago cost big bucks.
Oh one important item added was a 1:1 transformer for isolation i.e..
sparks....
There should be schematics around, I remember they added an Inductor to the
yoke, width controls did the same.

Anyway you can get a cheap NTSC to VGA converter and use PC monitor, it has
size adjustments.

"Clive Tobin" <clive@webband.com> wrote in message
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