wrote:

> Hello.. Some quick questions for those in the know..
> 
> Just picked up a spare IIGS off EBay as a backup for the ROM 03 I've
> been using for a while - and it turns out the thing is a ROM 00.
> 
> I've ordered the ROM 00->ROM 01 upgrade from Reactive Micro, however
> does anyone know:
> 
> A) How to identify if my board has the faulty VGC chip that came with
> many ROM 00's, and

Dredging my memory...

I can't remember the full part number, but it is easy enough to locate
the VGC on the logic board because it is labeled as such.

The faulty VGC had a part number ending with -0 or -A. The fixed one had
a part number ending with -C.

You can also check for the visual defect caused by the fault. It varies
somewhat between machines, but with my original IIgs, it was manifested
in 80-column text mode with white text on a black background (but not in
the default white-on-blue). Some of the pixels shimmered or appeared
pink in colour.

The dead giveaway is to use monochrome double hi-res graphics mode, e.g.
by running the original Apple II Desktop software which was supplied
with the ROM 00 IIgs before the IIgs Finder had been written.

It should be black and white (or grey due to dithering). The faulty VGC
has somewhat randomly located pink instead of grey.

> B) Is it still possible to obtain a replacement chip somehow (other
> than cannibalizing yet another IIGS?)

Can't answer that one.

> Second question: I've got a spare ROM 03 board that's giving a System
> Bad: 06010000.  I know this is a failure of the Serial test - is there
> a specific part I could check out and try and replace?

Looking at IIgs technical note #95, that specific error result is
"Serial test", and "Register read/write".

This suggests that the IIgs is unable to reliably access the SCC (Serial
Communications Controller), which will prevent either serial port from
functioning (one chip controls both ports). The chip in question is a
Zilog Z8530, surface mount variant. The problem might be something a
broken track or dry solder joint, or the chip may be damaged (less
likely).

Is there any kind of accelerator in the computer? If so, try disabling
it and repeating the self test. Some accelerators can cause spurious
failures of the self test due to the timing of the CPU being much faster
than the self test expects.

-- 
David Empson
dempson{at}actrix.gen.nz
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