Alternative Monitor for VAXmate

[Rob Jarratt]

> -----Original Message-----
> From: Tony Duell <ard.p850ug1 at gmail.com>
> Sent: 24 May 2020 03:13
> To: rob at jarratt.me.uk; Rob Jarratt <robert.jarratt at ntlworld.com>; General
> Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
> Cc: Paul Koning <paulkoning at comcast.net>
> Subject: Re: Alternative Monitor for VAXmate
> 
> On Sat, May 23, 2020 at 10:49 PM Rob Jarratt via cctalk
> <cctalk at classiccmp.org> wrote:
> 
> 
> > > > The horizontal sync has a frequency of 26.6KHz, active low with
> > > > the high voltage 3.7V, Vertical sync is 60Hz. I don't believe that
> > > > corresponds to any known standard, does it?
> > >
> > > I assume it's the same as the Pro video.  That might not exactly
> > > match standards.  But the intensity output is an acceptable 480i
> > > monochrome
> > video
> > > signal.  I've fed mine into a video capture device and into a TV
> > > display,
> > both
> > > work.
> 
> Err, no. The Pro (and Rainbow, DECmate II, etc) are TV rate. The horizontal
> frequency is 15.57kHz or thereabouts. Those machines  will work with TV-rate
> video capture devices.
> 
> [...]
> 
> > I have wondered about RGB, the I/O board does output an RGB signal
> > along with Intensity, Horizontal Sync and Vertical Sync, but I don't
> > know if I could feed that to a monitor that accepts RGB signals as I
> > don't know what the voltage levels should be. I have a VR241 which
> > seems to have suitable inputs but I don't know if I dare send the
> > signals from the I/O board straight to the VR241. I can't find a manual for it.
> 
> Again the VR241 is TV rate. The inputs are, I think, the normal 1V levels into
> 75ohms.
> 
> My experience is that sensible over-voltages on monitor inputs (e.g.
> 5V TTL signals into 1V analogue inputs) do no damage. It may not work, if it
> does it may look terrible, but it won't let the magic smoke out.
> 

Tony, are you aware of any device I could buy or circuit I could build to get a decent image out of it? It doesn't have to be perfect, but at least usable.

Thanks

Rob

> 
> -tony