Re: Apple II video problem?

Polymorph wrote:
On Aug 3, 11:16 am, "Michael J. Mahon" <mjma...@xxxxxxx> wrote:

Polymorph wrote:

On Aug 3, 5:49 am, "Michael J. Mahon" <mjma...@xxxxxxx> wrote:

MdntTrain wrote:

On Aug 1, 6:34 pm, "Michael J. Mahon" <mjma...@xxxxxxx> 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

NadaNet file server for Apple II computers!
Home page: http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it's seriously underused."- Hide quoted text -

- Show quoted text -


Thanks Michael, I figured you or one of the other hardware guru's
would know how to fix this.

Next time I feel brave enough to crack open the monitor case, I'm
going to give this a try.

Although I read posts from you and others about it being relatively
safe to work on a monitor due to low current, I still get a little
uneasy every time I see that "WARNING 10,000 VOLTS" sticker. ;-) I'm
in Australia too, and have 240V as opposed to your 110V which makes me
even more nervous. But I did it once before, so I'll give it another
go.

The put those stickers there to 1) warn off rubes, and 2) cover their
collective a**'s in case of a liability suit. ;-)

More seriously, you don't have to worry about the mains voltage once
the equipment is unplugged, and you don't have to worry about charged
capacitors (much) if the equipment has been off for a few minutes.

The exception to the last statement is capacitors that do not have
much load or other leakage to ground, which usually means high voltage
supplies. The good news is that the capacitances involved are pretty
small, so even at the high voltage, total energy storage is more likely
to be uncomfortable or startling than physically dangerous--with one
exception: the startle reaction can be dangerous in the vicinity of
a breakable CRT if you have a tool in your hand or might drop the
monitor!

The simplest way to proceed is to simply AVOID the anode connection on
the bell of the monitor, and the thickly insulated wire leading to
it. For almost all adjustments to a monitor this is easy to do.

The high voltage will not come out and get you if you do not come
within a half-inch of it, even if there is no insulation. (Of course,
if you have sweaty arm hairs, their length subtracts from the half-
inch. ;-)

If you *must* detach or otherwise work adjacent to the anode cap,
then attach an insulated wire to chassis ground (metal frame, etc.)
with an insulated, pointed metal instrument connected to its other
end (like a small screwdriver). Then with the now grounded instrument,
holding it by its insulated handle, gently insert it under the
rubber/plastic cap covering the anode connector and ground the anode.
Expect a "snap" as the spark discharges the anode capacitance and the
HV filter capacitor. LEAVE the anode grounded while working on the
monitor. (Remember to disconnect the ground before powering up the
monitor again. ;-)

Thanks again,

You're welcome!

-michael

NadaNet file server for Apple II computers!
Home page: http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it's seriously underused."
.

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