new find: an Intel MDS 800

From: Dave Mabry <>
Date: Wed Oct 27 06:19:25 2004

All this talk about my favorite computer systems is making me want to
fire mine up again and "play".

Steve, I never heard of an 8085-based cpu card for the Series II with
only 32K of ram. Are you sure about that version? I'd bet that was not
an option. I have several of both 8080- and 8085-based cpu cards.

As for the 8085-based system, if you have that in your MDS Series II it
was called a 225 or 235 (the 23X signifying that it was shipped with
double density controller boards and an external 2-drive case). The 220
and 225 were shipped with only the integral 8" drive and were
single-density as delivered. Anyone could "mix 'n match" after it was
delivered and make any version out of any version. So the model number
on the sticker on the back doesn't mean what the system has in it now.

Yes, Zendex made lots of cool boards for Intel multibus systems,
including the development systems. I think they made a one-board
diskette controller that could substitute for the two-board set from
Intel. I never used one but always thought it would be cool to have it.
  Save a slot.

And Jules, WELCOME to the fraternity!!!

As for the question of whether to replace failed chips with working ones
at the risk of making the systems "non factory original"...I totally
agree with Tony. WHATEVER it takes to make the things work!!!


Steve Thatcher wrote:
> as for the DC37 on the back (yes, they do consider it a d-sub style
> connector). The more important question is what the two bottom cards
> are in the card cage. They are normally a two board disk controller
> from Intel (bit slice processor). As long as the controller was made
> by Intel, then the DC37 pinout should be compatible with this
> hardware or Intel's. I seem to recall a company called Zendex that
> made compatible items for the MDS series.
> Intel made a MDS220 and a MDS230. In either one, you could make a
> choice as to the density of the internal drive. As I said before, if
> there is a 50 pin ribbon cable between the back board (IOC) and the
> drive, then it is wired for SD. If an internal cable comes from the
> front to the disk drive, then it is wired as DD. I have both types of
> cables at home...
> About your comment on monitor troubleshooting. I have the schematic
> set for the Ball Brothers monitor that was usually used in the MDS2XX
> series. The nice thing about the monitor is that it is very simple.
> There is no fancy monitor control chip in it, in fact it doesn't even
> have any chips on it if I recall correctly. The monitor was usually
> supplied by Ball Brothers or Zenith. The back IOC supplies +12V
> poower, vertical, horizontal, and video intensity signals for
> display.
> By the way, the top card with all the switches on it is the CPU card.
> There were three versions of it that I know of. The first was 8080
> based and only had 32K on it. I believe the remaining two versions
> were 8085 based with the first having 32K and the final one having
> 64K. If you only have 16 ram chips on your cpu board, then the next
> card down would or should be a 32K ram card.
> best regards, Steve Thatcher (one of the other MDS guys)
> -----Original Message----- From: Scott Stevens
> <>
>> The internal drive could be either SD or DD. If there is a 50 pin
>> ribbon connecting the drive to the back board in the system, then
>> you have an internal single density drive. If there is a cable
>> running from one of the front cards to the drive, then it has been
>> hooked up as double density.
> Actually, there's an added-in non-Intel jack on the back (I think 37
> pin 'D' shaped but as everybody knows, probably not a 'Dsub' due to
> size) that the external dual-8" floppy enclosure plugs into. I
> suspect the system may have had something third-party added to
> support the two external drives, and some of the disks are labeled to
> indicate they are 'higher' density than the internal drive will
> support.
Received on Wed Oct 27 2004 - 06:19:25 BST

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