Alternative Monitor for VAXmate

Tony Duell ard.p850ug1 at
Sat May 23 21:12:30 CDT 2020

On Sat, May 23, 2020 at 10:49 PM Rob Jarratt via cctalk
<cctalk at> 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.


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