Reviving a VAX-11/750

tony duell ard at
Mon Jun 15 13:33:07 CDT 2015

> > The bad thing with the 11/750 is that is has so many socketed TTL gate
> > array chips. Sockets are bad. And gate arrays are bad. In that sense I

Years ago I was offered an 11/750 and turned it down as soon as I saw
inside the cardcage. No way would I want to maintain that mass of 
custom gate arrays

> > think the 11/730 is better since it is AFAIK based on mostly standard off
> > the shelf chips.

> Mostly, if I'm not mistaken (I haven't gotten too deeply involved with the PCBs yet). 
> There are a number of PROMs.

There are 2 custom ICs in the 11/730 CPU (by 'CPU' I mean the 3 board set, DAP, MCT, WCS)
They are the memory ECC chips and are IIRC, the same as the ones in an 11/750, in other
words DEC used the same memory error correcting system. There are no custom ICs on
the IDT (disk controller), FP730 (floating point) or memory boards AFAIK. What is on Unibus
peripheral cards depends on what you have :-)

The rest of the CPU (and IDT, FP) is some TTL, an 8085, standand RAMs (SRAM and DRAM), 2901
bit slice ALUs, PROMs (in general the bit-dumps are in the printset, the only ones not there are the 
4K firmware for the 8085 console processor) and lots of PALs, again the logic equations for these
are in the printset. Oh yes, the TU58 controller board has a PROM on it that you don't get a dump of
but it is a standard TU58 controller so I assume somebody has dumped it.

So I am happy to try to keep an 11/730 running

The R80 disk drive has again, lots of TTL and analogue parts, an 8085 system using the Intel
8155 RAM/IO and 8355 ROM/IO chips (alas no dumps of the firmware in the prints ), a couple
of other sets of PROMs (no dumps :-() and a few custom head switching and servo preamp
ICs _inside the HDA_ where you can't really replace them. My view is that the R80 electronics is
repairable (and I must make a dump of the ROMs) but that the HDA is likely to be a problem area

There are some good 11/730 manuals on bitsavers. As well as the printsets (worth reading with a hackish
eye) there are technical descriptions of the CPU, Disk controller and floating point board. They refer to
a similar manual for the PSU which is, unfortuantely, not on bitsavers. Said manuals explain a lot of things
that are not totally obvious from the printset.

Things that I would love to see (but I suspect were never published) are a source of the 8085 firmware in
the 11/730 and a source of the standard microcode for said machine. Oh, and a source for the R80


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