Digital Rainbow 100 Workstation

The Rainbow 100 introduced by DEC in 1982. This desktop unit had a monitor similar to the VT220 in a dual-CPU box with both 4 MHz Zilog Z80 and 4.81 MHz Intel 8088 CPUs. The Rainbow 100 was a triple-use machine: VT100 mode (industry standard terminal for interacting with DEC’s own VAX), 8-bit CP/M mode (using the Z80), and CP/M-86 or MS-DOS mode using the 8088 and that’s what make it very interesting.
This is what it is supposed to look like


However our unit is missing the video cable to connect the base unit to the monitor. This cable also carries the keyboard signal to the base unit.

It is impossible to find one so I am trying to build one with a 15 pin terminal adaptor I found on Amazon

Let’s see how that goes first

This is the back of the monitor and base unit with the 15 pin port needed.



Do you have any documentation on these cables / connectors? You need the pinout of both ends.
The cable may not be 1 to 1. There may be some crossover pins. RS232 cables were often not 1 to 1.

The connectors you have are for prototyping.
So if you’re just trying to work out the right connections then these are good
But for a long term installation you need the cable solder type with the back shell.

Your cable is for video and keyboard. You could take a chance and try 1 to 1. But if the cable carries power and it is not 1 to 1 then you could damage something. Connecting outputs to outputs or RS232 ±12V to logic signals could also be a problem.

Sorry I can’t be of more help.
Good luck

Hi Andre
many thanks.

I have below the cable pinouts for all Cables that were made. The one I need is the BCC02 Mono cable.
If read the pinout correctly I only need to use Pin 4,5,6,7,8,12,14,15

Your right on the power as Pin 7,8 are +12v as it seems to provide +12 on both pins for the Monochrome version whilst pins 5,6 are the grounds with pin 5 is only for the monochrome version and pin 6 is ground for the keyboard.

I am planning on using this as a prototype tool and then create a real cable but my soldering skills on a cable pinouts are horrible. I find they are the worst to try and solder correctly.

This is from the official Rainbow manual that the second image references.

I have also attached a link to the Technical Manual which i am sure I’ll need along the way once the cable is created.

best regards

Hi Joe,

Having the manuals makes a huge difference. You’ve pasted section 3.5.3 J3 signals.
This looks like a 1 to 1 cable.

Pins 14 and 15 to mention input / output, but being RS423 I don’t think it would damage anything if they were accidently reversed. Have a look at RS-423 - Wikipedia

The DSUB connector should be relatively easy to solder using the “bucket” / solder cup type.


You can also buy ready made 1 to 1 DSUB cables. Just match the gender to what you require.
Try Jaycar, Element14, RS Components or


Ok finally back to it.
I had tried to get the cover off and it was stuck.
I finally managed to get the cover off and discovered the left side latch was stuck shut.
It needed some WD40 to release it.
Check out the rust on the release latch.

Then this started me checking the fan right near it

This was crusty so it had to come out.

Next Step Video Cable Creation…

1 Like

some success
Fan is back in and tried to power on. Nothing…
You need to remember to plug the fan back in and then power on or nothing happens
Ok so we have power on the base unit.

The cable is ugly but for now it does the job (sort of)

The screen has power from the video cable. Yayyyy,

I didn’t plug a keyboard in so nothing was working.

I plugged a keyboard in now and can hear something happening but nothing shows on the screen but when i press keys on the keyboard i can hear a slight click noise.

Back to basics

  1. check the video connections on the cable are right
  2. check it is the right keyboard
    3 clean the floppy drives and then try a floppy disc to boot

Stay tuned

This machine is doing my head in
At the back there are seven led diagnostic
It shows what the error is and how to resolve
Currently ALL seven are lit, grrrrrrrrrr
This is going to a pain
Time to pull it all apart