I should try to figure out exactly how the video
encoder works in these
things. I hear the design is a bit... creative. Maybe there's a decent
description on the web somewhere.
Actually, the video timing chain looks quite conventional.
> Silly question of the day: I'm guessing
no-one would have any idea where
I'd
find a 14.25045MHz crystal in New Zealand...
No, but the standard crystal in an
Apple ][ is a 14.318MHz crystal, and
that's a standard so should be very easy to find. I wonder if yours is
a special value for a non-US market? But AFAIR even the Apple Europlus
used 14.318MHz.
This is the value I remember from many years ago when I used to mess about
with these machines. It would explain why the crystal was floating in the
air rather than glued to the board as it normally is. Looking carefully, it
looks like someone has had a fiddle with a few of the frequency settings.
The 50/60Hz pads have been changed from default, too. I expect this machine
was imported into NZ (probably from the US) when it was relatively new, and
someone's converted it to the local frame rate. Seems strange when most
monitors would have worked with it as it was.
Pondering... if this machine has 50/60Hz pads to switch it over, why would
anyone need to replace the crystal? It seems a bit odd.
The cut/jumperpads appear to change the numebr of lines per frame only.
In other words, in the '60Hz' position, you get 525
line 60Hz video. If you changthe padsettings, you'll get something
_close_ to 625 line 50Hz video, but with the US horizotnal frequency
(15750 Hz) not the European one ((15625 Hz). Most monitors will hve no
problem wit htat at all, of course, but some things might.
What is the current setting of the pads?
-tony