VAX 11/750 rescued, alas...

Ethan Dicks ethan.dicks at
Sun Oct 7 02:54:51 CDT 2007

On 10/6/07, J Blaser <oldcpu2 at> wrote:
> Ethan Dicks wrote:
> > I did notice you have a cable hanging down for a UDA50... it's likely
> > that they had both SI disk _and_ Unibus-attachd SMD disks.

Grrr... I _meant_ *SDI* disks, not SMD. RA81s, RA90s, etc.

> Oh, yes, thanks for the reminder.  Indeed there are about a half-dozen
> carts floating around in the bottom of the cabinet.  I haven't even
> extracted them yet to see what they are.  But I'll definitely want to
> get an image of them, if I can, once the drive is revived.  I wonder,
> can the integrated TU58 be (temporarily) cabled to something like the
> PDP-11/23+ that I have, so that I could image those carts first before
> trying to use them in the VAX (eventually)?  Is it just a standard
> serial connection coming off of the drive, like the desktop TU58
> subsystems, or is it something lower level?

Electrically, it's a standard serial interface, but I think there
might be an odd cable because it's an 11/750-internal cable.  Nothing
insurmountable with a willingness to make a cable adapater.

Yes, you could use an 11/23+, or even a modern machine running DOS or
UNIX and one of the several TU-58-slurping programs out there.

I personally use a dual TU58 from an 11/725 and a PC to read my carts.
 I forget, at the moment, which program I'm using, but it's one of the
old, standard ones that's been kicking around for years.  I have about
an 80% success rate with the tapes I've read so far.

Oh... you could eventually substitute a PC or FLASH-based TU58
emulator in place of the drive, but in practice, we only ever used our
TU58 for booting diagnostics or Standalone Backup for OS installs, or
loading the DEC Microcode patch... come to think of it... the
Microcode patch (which we started using around VMS 4.6 or 4.7) would
be an excellent use for a TU58 emulator.  Software-based ones are out
there, just like the tapedumping packages, but except for an ancient
8051-based Spare Time Gizmos hardware TU58 emulator (now out of
production), I don't know of any hardware TU58 emulators, but every
once in a while, I kick around the idea of building one (with a CF
socket for storage, and an LCD to see what the emulator is doing).

> Looks like this is going to be a somewhat lengthy revival, with lots of
> things to consider, detail-wise.

That seems likely.

> Actually, I just can't see myself scrapping the machine.  It would be a
> real shame to do that, so I'm going to do my best to get the backplane
> repopulated, cobble some storage, and light it up!

Good to hear.  Keep up the good work.


P.S. - as for adding wires to the backplane, any wire-wrap tool should
suffice, including the manual tool that Radio Shack used to sell
(looks like a Jeweler's Screwdriver, with a wire-stripper stored in
the handle).  No unusual tools (beyond ordinary WW tools) are

P.P.S - if you are *lucky*, there are plastic alignment blocks on the
backplane where the cables tap into the off-board I/O area.  If not,
you might want to track down the installation manual for the SI
9700/9900.  More with Massbus or Unibus adapters, I've seen 2x20
plastic blocks that slide down over the pins to help connector
orientation and registration, but they aren't required, as long as you
get the cables on right the first time.

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