Re: Can the IIgs output colour on its composite monitor output?

[david@uow.edu.au (David Wilson)]

"ralmin" <xbiber@bigpond.net.au> writes:

>> David Wilson wrote:
>> Ralmin wrote:
>> >David, I cannot see any way how this can be an NTSC IIgs. Are you
>> >completely certain none were made? It's ROM 3.
>>
>> According to the A2 Central newsletter, Apple Australia did modify some
>> IIgs systems to output PAL color (it was required for them to be able
>> to sell the units to schools). It should be easy to identify these
>> systems as the color generator chip was removed and a small
>> daughterboard put in its place. I have never seen one in person.

>This IIgs did come from a school (it's engraved St Felix School, Bankstown).
>I can't see any daughterboard on the motherboard though.

It would be under the power supply. I had a look at my ROM03 motherboard and
the color encoder chip is the 20 pin MC1377 next to the battery. This chip
is able to generate both NTSC and PAL signals provided pin 20 (the PAL/NTSC
select input) is set to the correct level AND the oscillator on pins 17 & 18
is running at the correct frequency (3.58MHz for NTSC and 4.43MHz for PAL).
You ground pin 20 for NTSC and leave it unconnected for PAL according to the
Motorola data sheet. I did have a look at the circuit in the back of the
IIgs Hardware Technical Manual but I did not have the MC1377 data sheet at
the time so am unable to confirm how pin 20 was wired.

There is no source of 4.43MHz on my ROM03 motherboard. If you wanted to check
to see what the IIgs was generating measuring two pins would suffice I think:

Pin	PAL	NTSC
--------------------
17	4.43MHz	3.58MHz		OSCin
20	o/c	GND		PAL/NTSC

According to the article in A2 Central, as Apple was soldering the MC1377
into IIgs motherboards the upgrade to PAL was accomplished via a motherboard
swap.
--
David Wilson  School of IT & CS, Uni of Wollongong, Australia