Reviving a VAX-11/750

Mattis Lind mattislind at
Mon Jun 15 13:06:34 CDT 2015

2015-06-15 17:32 GMT+02:00 Mark J. Blair <nf6x at>:

> I wasn't aware that you are working on a 750 repair. Congratulations on
> the progress you have already made! Are you using real console tapes,
> tu58em, or something else?

Well. I am probably working on to much simultaneously. But this machine is
100 km away so it is just now and then I do something with it. Like this
weekend. The real console tape tape drive is in questionable status
although not tested. I tried to use the mockup I did based on the TU58
emulator by Bela Török. But I wasn't successful (I had it working
previously on an LSI-11 so I am not sure what is wrong - I guess that I
told that it was working perfectly previously - well I was wrong).

Then I compiled your fork of tu58em on github. And it worked perfect. I
didn't need to use the special vax mode that you have implemented though.
Maýbe it is required only by 11/730?

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

In a way I am happy that is indeed running the BOOT58 program and several
of the diagnostics but it sure would be very interesting to know why this
Translation Buffer / Cache diagnostic fails. Were there any listings
available for the VAX diagnostics? The micro diagnostics run in the RDM
module is pretty well described in a document on bitsavers. There are no
details though. But for the native VAX-11 diagnostics I can not find

Next step would be to create a SCSI disk with a VMS installation on it.
Hopefully I manage to do that using SimH. I don't have any nice TU80 to go
with the machine so it is not possible to do an install from tape. I do
have a lead on a TU81 PLUS, but it is some 900 km away currently...


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