DECmate III and Rainbow 100+

[Tony Duell]

> 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