Re: DEC Rainbow



     Date: Sun, 22 Aug 1999 01:56:14 +0100 (BST) 
     From: ard@xxxxxxxxxxxxxxxxxxx (Tony Duell) 
     Subject: Re: DEC Rainbow 



> 
> Hi.  I just acquired a Rainbow (haven't seen it yet, so I don't know 
> many specifics) but it has a color monitor and the guy said he also 
> had a touchscreen attachment for it.

I've never heard of a touchscreen for the Rainbow, and I suspect, 
therefore, that it's a 3rd party thing.


> 
> Anybody have pointers to where I can find out a little more about 
> this beast? The guy I'm getting it from told me it was working the 

I can tell you a little about the hardware. The motherboard contains 2 
processors (8088, used for CP/M 86 and MS-DOS, and a Z80, used for CP/M 
80), 128K (normally) of RAM, BIOS ROMs, a text-only video output 
(essentially the video circuit from a VT100), a couple of serial ports 
(one for the 'comms' (modem), one for a printer -- note the DB25 on the 
back is _not_ a parallel port), keyboard interface, and a lot of TTL 
glue. There are no expansion slots as such, but there are connectors to 
allow up to 4 boards to be fitted on top (each board has a particular 
position that it goes in).

All machines have the RX50 (floppy) controller down the RHS. This is a 
Western Digital 1793 chip + support logic

At the front left you'll have a 'colour card'. This is complex. It's got 
an NEC 7720 graphics coprocessor on it, along with 64K of video RAM, 
colour look-up table and more TTL glue. This is needed if you have a 
colour monitor in the system, but you can also use it with a mono monitor 
(to give bitmapped graphics, since the 'bow motherboard video is 
text-only). 

Behind that you might have a RAM card. There are 2 versions of this (at 
least). The older one is a plain 192K card. The later one will take up to 
3 banks of chips, either 64K in a bank or 256K in a bank (any mix). Yes 
you can have 896K of RAM in the machine.

Behind that, across the back of the machine is the 'general purpose' 
expansion slot. The 2 connectors for this have just about every signal 
you could want on them. The most common card to find here is the hard 
disk controller (WD1010 + support chips), which links to an RD51 (10 
Mbyte MFM drive, probably an ST412). There was also a comms card that 
went here, but I've never seen it.

The unit can be dismantled without tools [1]. Under the sides of the case 
are 2 little catches that you slide forwards and flip out to release the 
cover, which then lifts off. On top of the chassis are the drives 
(there's always an RX50 in the RH bay, and sometimes another RX50 or an 
RD51 in the LH bay). You can remove the drives by unplugging the cables, 
releasing the spring catch under the front edge of the drive, and 
sliding it out. 

Across the back of the upper chassis is the PSU. To get that out, unplug 
the power cables from the motherboard, drives, and fan/switch assembly, 
release the clip on the left end and swing it up and out.

To remove the 'logic module' (motherboard and all the cards), unplug the 
power cable (thick ribbon cable) and the drive cables from it (there's a 
hole in the rear right of the chassis). Loosen the 4 black thumbscrews at 
the back, and slide the cards out of the back of the machine. You can 
frob the clips on the standoff posts and unplug the cards from the top of 
the motherboard.

[1] I really have never seen the point of such cases. You need a 
soldering iron, logic analyser, etc to fix the machine anyway, so having 
a screwdriver is no big problem. And anyway, to take some of the Rainbow 
modules apart (like the PSU), you do need screwdrivers.

The keyboard is a plain LK201. The colour monitor is a VR241 (plain 
TV-rate sync-on-green). You'll get a cable with a DA15 on one end (goes 
into the connector on the back marked 'video', and a box on the other end 
with 3 pigtails/BNCs (to go into the monitor) and an RJ11 (for the 
keyboard cable).

The RX50 disk drive is strange. It's 2 drives in 1, sharing a common 
spindle motor, head stepper, etc. The top disk (drive A IIRC) goes in the 
normal way up.. The bottom disk goes in upside-down. If you have genuine 
DEC RX50 disks, then you line up the orange arrow on the disk with the 
orange line on the front of the drive.

If you want to look inside the RX50 (and you should - once....), take it 
out and take out the 4 screws on the mounting skid on the bottom. The 
metal can then slides off backwards. Dismantling it further is possible, 
but it's not that easy. (I've done it, though, and got it back again).


-tony