Re: Problem 2: no color -Re: Vertical Sync Issues with modern TV

[Mike Willegal <mike@willegal-nospamplease.net>]

Yes,
   I think I understand what is happening.

   I believe that the Apple in question has a PAL 14.25 MHZ crystal in 
it.  I'll see if I can find and swap in a NTSC 14.318 MHZ version and 
see if that does the trick.   This unit would appear to be a Europlus
configured board in a regular plus case.  It also has a non-standard 
keyboard, but I've assumed that it is an aftermarket replacement.

   The color burst signal should be 3.579.  With the PAL crystal, the 
resulting color burst of 3.56 MHZ must be too far off to work.

   Both PAL and NTSC have color burst information in the horizontal sync 
signal, however it doesn't appear that the Apple II natively supported 
color PAL, but I'm not sure about this.   Perhaps that was the reason 
for the additional PAL encoder card that was available in PAL markets.

   One final observation, it appears that the CPU on PAL configured 
Apples runs slightly slower than NTSC Apples.   1.017 MHZ vrs 1.023 MHZ

   Regards,
   Mike Willegal
   


In article <OSQ5d.268624$Fg5.250456@attbi_s53>,
 glen herrmannsfeldt <gah@ugcs.caltech.edu> wrote:

> Mike Willegal wrote:
> > Ok,
> >    Those old boards were designed to work as PAL or NTSC.  Cut a couple 
> > of traces and add some blobs of solder to convert.  Didn't notice the 
> > difference until I compared it to a "working" NTSC board. 
> 
> >    New Problem:
> >  I've changed the  board back to NTSC, but now I don't get any color.   
> > Tried two different TVs and an RF modulator.  My other board of the same 
> > vintage also doesn't exhibit any sign of color, either, though it never 
> > had the issue with PAL sync timing.   I do get shades of grey.
> 
> Besides the different sync frequency, NTSC needs the color burst
> at the beginning of each line.  I forget whether PAL needs that, but
> even so it would likely be different.
> 
> It might be that a different jumper sets that.  I had an apple2
> schematic about 20 years ago, but I haven't looked at one since.
> 
> -- glen
>