Re: Apple II video problem?

["Michael J. Mahon" <mjmahon@aol.com>]

Polymorph wrote:
> On Aug 3, 5:49 am, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
> > MdntTrain wrote:
> >
> > > On Aug 1, 6:34 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> >
> > > > Not laughing, but wondering whether the horizontal hold control
> > > > (inside the case) could have made the two cases much more similar...
> >
> > > I can still try that.  Right now, I have HHold adjusted perfectly
> > > centered between the two points of going crazy (losing sync?).  Moving
> > > it one way does cause, at one point, the left shift video to suddenly
> > > shift more towards the center.. but it was near enough to the "going
> > > crazy" spot that I didn't feel secure leaving it there and opted for
> > > the middle.   I did not try plugging in the Rev 7 board at that spot
> > > to see what happened either.
> >
> > > What are you thinking?
> >
> > I'm thinking you have it correctly adjusted at the midpoint.  ;-)
> >
> > Some monitors have horizontal phase lock loops that respond to
> > the average (middle) timing of the horizontal sync pulse, while
> > others (digital?) will respond more to the leading edge.  This
> > could make the difference in horizontal phase, since the leading-
> > edge-to-start-of-window timing is apparently nearly constant across
> > models.
> >
> > -michael
>
>
> I have a different, but similar (I think) problem with one of my IIgs
> monitors. It displays a reasonable image, however the whole thing is
> on a slight lean. That is, one top corner of the display is slightly
> higher than the other (can't remember which right now - I'm at work).
>
> I tried messing with the centering rings inside the case, but gave up
> as I couldn't seem to remedy the problem. By turning the centering
> rings, I could change the "tiltedness" somewhat, but at the cost of
> image quality (colours became separated and image deteriorated
> greatly). So I gave up and returned the image to its original state
> (or as close as I could get it). I may have actually made it worse
> rather than better, as I am sure the image was a bit sharper before I
> twiddled with it (maybe its just me be negative though).
>
> Although I resigned myself to the fact that the image would remain on
> a slant (and I have kinda got used to it), can anyone suggest
> something else that I could try to realign the image? Could it be the
> result of some component(s) approaching their used-by dates? Maybe
> some ageing capacitors or something?

The solution is to rotate the yoke on the neck of the CRT.

It is common for the plastic liner of the yoke to have some stiction
with the glass of the CRT neck, and there is a "hose clamp" around
an extension of the yoke whose purpose is to keep it from moving
relative to the CRT, but carefully loosening the clamp will allow
the yoke to be turned (or moved backward, which you don't want to
do) to align the raster to the CRT bezel.

It's really pretty easy, but be careful not to apply too much or
too sudden pressure to the glass neck.  It's strong, but not
unbreakable.  ;-)

You will find a mirror helpful, as well as a program to display,
say, a white HGR screen to make alignment easier to see.

Generally, centering will be unaffected, but if it needs adjusting,
this would be a perfect time to trim it up.

-michael

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