Re: Problem Using a Commodore 1084s Monitor on a IIgs

[Polymorph <polymorph69@hotmail.com>]

On Feb 11, 6:32 am, "Michael J. Mahon" <mjma...@aol.com> wrote:
> Polymorph wrote:
> > Now, as you can see from the above images, it doesn't appear to be
> > fully synched. All the characters are leaning to the right (like
> > everything is in italics), and you can see the black area on the RHS
> > of the screen which is wobbling around a bit.
>
> This means that the horizontal sync is not quite right, either.
> You could adjust the horizontal sync on the monitor to get it
> closer, or....

Michael, as per all of the IIgs-->1084 FAQs suggest, I've only
connected the composite sync from the IIgs to the composite sync of
the 1084. Also note that in the 1084 the composite sync and horizontal
sync are tied together (the 1084S-D schematic I found confirms this).
I have left the vertical sync not connected as per the Apple II FAQ.

> > I'm thinking that in my case, 75 Ohms is not quite right, but
> > something in the vacinity would be right. Does this sound plausible?
> > Do you recommend that I buy a variable resistor and try and find the
> > optimum value? Or should I being trying something else.
>
> Exactly.  Try lowering the value (or, better, adding a 75 to 150 Ohm
> pot with the IIgs driving the "high" end and the output to the monitor
> coming from the center terminal) until you can find where the sync
> drops out because the level is too *low*.  Then increase it until good
> lock is achieved.

Just so I am clear, when you say "lowering the value" do you mean the
voltage on the composite sync - i.e. lowering the resistor value used?
If that is the case, wouldn't I need a resistance of less than 75
Ohms, meaning a 75 to 100 Ohm pot would be too much resistance? Please
forgive me if I'm talking rubbish.  ;-)

I took a look at the catalog of my local electronics dealer (Jaycar),
and they have a variable 0-200 Ohm variable resistor (this is the
smallest variable resistor they have).  I'm thinking one of these
would fit the bill, what do you reckon?

> You may still find it worthwhile to adjust the vertical and horizontal
> hold controls to the middle of their stable ranges.  It seems that
> this monitor's settings may have drifted a bit.

The vertical hold was very difficult to adjust to get the image to
stop rolling - i.e. there is a *very* small stable range for the
vertical hold. But it was possible, as the images I posted previously
confirm. I am guessing with a different resistor value this problem
will rectify itself. This problem with vertical hold was only present
using the RGB port however, when I hooked a DVD player up to it via
the composite ports I had no such problem.

> > What would you guys recommend as the next course of action? All
> > comments welcome.
>
> You're almost there!

Great! I was hoping you'd say that.   ;-)

Thanks for your help,
Mike