Re: Vertical Sync Issues with modern TV

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

This is getting more interesting.  It appears from an Oscilliscope that 
the vertical refresh is cycling at 50 HZ.  The board came from ebay - 
and is marked copyright 1978.  Did apple make a PAL type board in that 
timeframe.  There is no rework visible, so it either has a strange 
problem in the ls161 dividers area or was built for a PAL type 
application.  It came with a PAL encoder board and a universal power 
supply.

The Taxon Monitor must be very tolerant of veritcal refresh rates.

What do you guys think?

Regards,
Mike Willegal




In article <20040921013815.23955.00000873@mb-m16.aol.com>,
 mjmahon@aol.com (Michael J. Mahon) wrote:

> Mike Willegal wrote:
> 
> >   My Apple II's seem to work fine with the old Taxon monochrome monitor 
> >I have, but vertical sync appears to be an issue with recent color TVs 
> >(with no apparent external vetical sync controls).  Tried both an RF 
> >modulator and composite video, but vertical sync  doesn't lock on two 
> >different TVs.
> >   Any ideas?
> 
> It's unlikely to be a scan frequency problem, since the Apple is
> very close to standard.
> 
> More likely, the transistor/resistor matrix in the Apple that generates
> the "blacker-than-black" sync pulses is making them a little too
> weak.  They should be about 0.3 volts below black for a (nominal)
> 1v peak-to-peak video signal.  Unfortunately, it will take a scope
> to check this directly.
> 
> Another possiblity is that your TV's are either overloading (more
> likely) or expect a video input of greater amplitude than that provided
> by your Apple (less likely).
> 
> The fact that this happens with more than one Apple II argues for
> a level or sync anomaly with the TV set (or is it really "sets"?).
> 
> -michael
> 
> Check out parallel computing for 8-bit Apples on my
> Home page:  http://members.aol.com/MJMahon/