DECmate III and Rainbow 100+

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Wed Feb 23 18:45:12 2005

> It's in the Pro 300 technical manual, on Al's website.
>
> The video connector is a bit weird. It carries both a mono
> (grayscale) signal with standard sync, and also on separate wires an
> RGB signal with sync on blue (not on green). Don't know if the
> Rainbow and DECmate have a color option, but the Pro does and that's
> where it goes.

I would check that very carefully (in other words : It doesn't agree with
what I've seen).

The standard colour monitor for this series of machines is the VR241.
It's acatually a Hitachi chassis with a vile PSU design, but I digress.
It can take RGB + separate composite sync (on 4 BNCs) or RGB with
sync-on-GREEN. I have the schematics to prove the latter statement...

My VR241 came with a Pro350. The Pro's video cable had 3 BNCs on the end,
and certainly used sync-on-green (there may well be sync on the other
video signals too). IIRC the Pro outputs a separate mono composite signal
that can be used to drive the VR201 mono monitor.

The 'bow does have a colour option, it's a card with an NEC 7220 video
chip + RAM + logic on it. Now the 'bow's video output is slightly
different ot the Pro, in that the stnadard way of using the colour
monitor is to use the _mono_ output (which iis mixed with the green
output from the colour card, and which includes the sync signals) to
drive the green input of the VR241, and the R and B outputs of the colour
card to drvie the appropriate outputs of the VR241. The green output from
the colour card (not mixed with the mono video from the mainboard) is
brought out and it's possible to use that to drive the green input of the
VR241 and link a mono monitor to the mainboard's mono output. If you do
this, you don't get the normal text-mode (VT100-compatible, it's the same
chipset) output on the colour monitor at all (if you use the standard
configuration, it appears in green on the colour monitor).

I've made up a universal video cable which brings all the 4 video signals
out on BNCs, has a modular jack for the keyboard cable, etc. I can
provide details if anyone wants them.

>
> And yes, the whole thing is powered, rather poorly, from 12 volts.
> (Poorly: if you flip significant quantities of white pixels on and

I've never had this problem. Are you sure you've not got some dried-up
capacitors somewhere?

> off, the scan area expands and shrinks very noticeably. So clearly
> the supply regulation is seriously inadequate.)

-tony
Received on Wed Feb 23 2005 - 18:45:12 GMT