Re: VGC

[dempson@actrix.gen.nz (David Empson)]

Tinman <Tinman@cottage.ecore.fnet.org> wrote:

> A while back, there was a thread discussing the VGC chip in the IIGS and
> the effects that some of these chips had on the double-hi-res screen, etc.
> I recall someone (don't remember who)

That would be me.

> saying that the chip number on the "good" VGC is 344S0046-C.

I said that this is how my replacement VGC is labelled, so it is known
to be a good one.

> The "bad" VGC's ended in -0 or -A.

I wasn't sure, because I haven't seen my original VGC since 1988 and
didn't think to make a note at the time (I got to keep the old ROM, but
not the VGC).

> I finally got around to looking at my VGC, and the number is 344S0046-1.
> Is this a "good" chip or a "bad" chip?

Probably a good one.  I knew there were other versions, but I didn't
know how they were labelled.  I have no idea what differences there are
between the various versions.

It is only the original version which has the fault.  This was shipped
in the first few thousand ROM 0 IIgses, and I think all of them were in
machines with a "Woz" label on the case.  If you have a machine that was
shipped as a ROM 1, then you definitely don't have a faulty chip.

To check whether your VGC has the problem, you need to run a program
that uses monochrome double hi-res graphics mode.  An example is
MouseDesk 2.0, or Apple II Desktop (included on IIgs system disks 1.0
through 2.0).

On a good VGC, everything in monochrome double hi-res mode appears as
black, white or grey.

On a bad VGC, you get pink stripes, pink flickering, or pink fringing
effects.  On some chips, this can also happen in 80-column text mode
(but only with some combinations of foreground/background colours).

If you can't locate these programs, then nearly any other program which
uses double hi-res graphics will do - just make sure the display is set
to Monochrome in the Control Panel before running the program.
MouseDesk and Apple II Desktop change the mode to mono double hi-res
without adjusting the Control Panel setting, so if you have the display
set to colour in the Control Panel, then going into and out of the CDA
menu gives you a coloured MouseDesk desktop, which is rather hard to
read anything on, and will not show the problem.

If anyone out there does have the "bad" version of the VGC, can they
please tell me what part number it has, so that we can avoid confusion
of this nature in future?

-- 
David Empson
dempson@actrix.gen.nz
Snail Mail: P.O. Box 27-103, Wellington, New Zealand