Re: Vertical Sync Issues with modern TV

[mjmahon@aol.com (Michael J. Mahon)]

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

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