"Peabody" wrote in message
...
Arfa Daily says...

Is there not a set HT pot in the power supply ? Usually,
turning this down by a few volts will shrink the picture
all round. You can then just correct the vertical via
the menu.

I have a fair amount of experience with digital circuits,
but not analog, and particularly not television. So I know
you'll understand when I ask:

Is HT the flyback transformer? If so, are you talking about
the source that supplies the primary of that transformer as
well as the deflection coil? It's 134V on the schematic.

If so, that is controlled by a STR30134 regulator. There
are no pots there, but there is a pair of fixed resistors
as a divider that appear to control the output voltage, and
I'm sure I could insert an adjustment there if that would do
it.

I'm actually surprised that you feel that you have that
degree of overscan that it's affecting your viewing. If
you really are missing actual picture, then it must be
significantly more than the 'normal' 7 - 10% raster
overscan.

It has been this way since it was new, so it's not an aging
problem. I've always had the sense that I was missing part
of the picture, and when I got a DVD player that also lets
me zoom OUT, the difference became apparent. It may
not be more than 10%, and perhaps others would not object to
it, but I would just like to see what's actually in the
picture, rather than a cropped version.

Remember that the broadcast picture is not as wide as
the scanned raster, and a lot of the relationships that
we used to use to judge picture width, have now gone out
of the window, with all the different 'widescreen'
formats that they keep broadcasting now, and which many
older TVs just don't look good on. Have you actually
looked at the picture on a proper 4:3 test pattern ?
It's the only way really to make a valid judgement on
the picture geometry.

No, I don't have any service equipment beyond a multimeter.
The problem shows up more with the DVD player than on
broadcast, particularly when playing things like mpeg1
videos that I've downloaded. Probably because in that
situation, the full raster is used.

You may of course have an actual fault. It's not at all
uncommon for the values of the components in the set HT
circuit to drift, resulting in a slowly 'growing' scan.

I don't think so, and I don't have the sense that it's
getting worse. I think it's just the design of this set.
But if it's possible to fix it, I would like to.

Thanks very much for your help.


"Set HT" refers to the 134v. Some manufacturers call this the 'HT' and the
output of the flyback transformer 'EHT' or 'HV'. Others call the output of
the flyback simply 'HT' so there's no 'definitive' answer to that question,
but it all boils down to the same thing in the end, and this variation in
terms is just accepted. Altering the supply voltage to the H-OP stage - ie
making the 134v something different - will affect the overall raster size,
as well as affecting the high voltage output from the flyback Tx. Tv sets
normally have an overvolts protection circuit, to stop the flyback voltage
becoming excessive, as this could result in the CRT emitting x-rays beyond
the maximum allowed limit. I think that before getting complicated with
adding L and so on in the deflection current path, I would first try making
the 134v slightly adjustable, and just seeing whether that does it for you.

Arfa