Sync on Green RGB video

Lyle Bickley lbickley at
Sat Nov 18 17:54:45 CST 2017

On Sat, 18 Nov 2017 18:44:07 -0500
william degnan via cctech <cctech at> wrote:

> On Nov 18, 2017 4:09 PM, "Douglas Taylor via cctech"
> <cctech at> wrote:
> >
> > I have a couple of vaxes that output 'unique' video, Alpha 3000
> > 300,  
> Alpha 3000 400, Vax 4000 VLC, and Vax Station 3100 M76.
> >
> > The Alpha and VLC each have a 3W3 type of connector and the 3100
> > has a 15  
> pin DEC designed connector.
> >
> > What does it take to connect these to inexpensive, modern VGA
> > light  
> weight monitors?
> >
> > Doug
> >  
> I have played around with that problem.  If you have a converter to
> get into a VGA port a newer high-end vga display will be able to
> adjust, but not a cheap one.  Because I use my vice vga/digital
> display for mode stuff, I use a huge SGI color display for all of my
> 3w3 outputting systems and I just switch the cable around.  If you
> could imagine 5 or 6 systems clustered around the one display.
> I am sure someone here has a technical explanation, but in a nutshell
> the 3W3 world signal isn't the same as a standard vga and cheap vga
> displays can't handle the refresh rate.  Someone will prob. refine my
> answer but that's why you can't just stick an adapter on there.
> Bill Degnan
> twitter: billdeg

The "issue" is "Sync-on-Green". Many *NIX and DEC systems that have RGB
output do NOT use a Hsync signal - but rather sync is placed on the
"Green" channel.

If you use any monitor capable of "sync-on-green", and it should work.


Lyle Bickley
AF6WS    '73
"Black holes are where God is dividing by zero"

More information about the cctalk mailing list