VAX 11/750 rescued, alas...

J Blaser oldcpu2 at
Sat Oct 6 15:05:24 CDT 2007

Ethan Dicks wrote:
> On 10/6/07, J Blaser <oldcpu2 at> wrote:
>> The first is a System Industries 9700-6301
>> with the following significant chips: Signetics N8X60N, AMD
> That looks to me (from appearance and the part number) to be the
> 11/750-specific SI-9900 interface.  I have one in an 11/750 in my
> quonset hut.  SI made a number of host-specific interfaces (Qbus and

Ah, okay, that's helpful.  I'll keep that in mind as I do more 
background research.

> For the case of what you have there, you should also have a pair of
> 40-pin cables going off the backplane for that slot, out to an I/O
> bulkhead header.  There would then be a pair of (possibly shielded)
> 40-pin cables running off to a 5.25"-tall rackmount box marked "SI
> 9900".  It should have at least one host board to receive the pair of

I'll check that, and see.  So, is it normal that a lot of the 
connections for this system come off the backplane, rather than headers 
on the PCBs themselves?  Hmmm.....  No wonder the reverse side of the 
backplane looks so hairy!

> 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.  That was a
> common arrangement for a variety of reasons.  You will also want to be

Yes, looks like the SMD cabling is in there, but I haven't even gotten 
so far as seeing where it might run to.

As it turns out, I _do_ already have an RA81 (and two Fujitsu Super 
Eagles) that came along with a separate pickup of some qbus stuff a 
couple of years ago.  Maybe I now have a use for these drives, assuming 
they are functional!  ;-)

> on the lookout for a DU boot ROM.  The 11/750 didn't use the TU58 for
> boot files as the 11/730 and 11/725 did.  You just twisted the ROM
> selector to the right device, then pressed reset/boot.  the D ROM was
> typically the TU58 boot (DDA0?) so you could boot tape-based
> diagnostics.

Okay, good words, thanks for the heads-up on this.  I am absolutely 
novice with this system, so all suggestions and advice are very welcome!

>> The second board is an MCD MLSI PC-11,
>> which I'm guessing may be some kind of dual parallel
>> interface.  I'll have to do a little scouting on Bitsavers
>> and Manx to see if I can turn up anything useful.
> If you don't find anything, the board looks to me like a papertape
> punch/reader interface.  Try throwing that into your searches.

I'll give it a go and see what turns up.

> Good luck on finding boards.  They are out there, but I doubt they'd
> be inexpensive from a dealer.

I've been fortunate enough to already receive some helpful offers (you 
guys know who you are!).  It just depends on what specific pieces can 
rationally be cut loose by their current owners.

> The other thing to do, and I don't have the docs handy for this, is to
> check your backplane in the memory area, to confirm what it's wired to

Ooo, sounds like I've got some interesting self-education ahead of me!  
:-)  Wiring backplanes has definitely not been in my experience...yet!   :-o

> Don't let this worry you until you get enough boards to throw together
> into a CPU... just get some memory - 1MB boards _should_ be safe -
> then worry about which memory controller you find next.  256KB boards

Great advice!  Make sense to me.

>> say that the donor was extremely nice, and offered to pass
>> along anything related that eventually turns up as they dig
>> deeper into their massive pile (12' x 15' x 20', literally
>> boxes/cartons/PCs upon boxes/cartons/PCs), but I'm not sure
>> I should hope for much.
> Have them keep an eye out for that SI disk box - it's the other half
> of the board you already have.

Yes, they are.  While making the pickup, we thought we saw another 
cabinet just peeking out from under the huge lumpy pile, but it turned 
out to be a telephone switch, I guess used as the in-house PBX by the 
former owners of all of this stuff.  Anyway, the donor is aware that 
these big VAXen were coupled with external storage devices, and is 
looking out for other cabs.

> P.S. - don't forget to pick up a short length of 1/2 ID Tygon tubing
> to rehab the TU58 roller.  

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?  I guess I'll have to climb 
in there and take a look, and scout the docs for more info.

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

> If you _do_ eventually have to scrap out
> the machine, save the backplanes, PSUs and TU58 for other 11/750
> owners.  

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!

Thanks for the advice and encouragement!  Keep it coming!

- Jared

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