Microvax II 'primer'?

allison allisonportable at gmail.com
Mon Jan 22 13:50:51 CST 2018

On 1/22/18 8:43 AM, Jules Richardson via cctalk wrote:
> On 01/21/2018 04:04 PM, Rob Jarratt wrote:
>> You might find that the filter capacitor goes up in smoke soon after you
>> connect the PSU to the mains, even without powering it on.
> Yes, Adrian Graham mentioned that (via FB), too. I seem to have 
> extremely good luck with the RF filter caps, unlike other people, but 
> I'm always prepared for the cloud of smoke :-)
I have several BA23 boxes both PDP11 and MicroVAX and never had this 
I may be a Eu (230V ac) issue.

>> Otherwise it is certainly wise to check the PSU visually for any 
>> obviously
>> failed electrolytics. If  you have one of the DEC load boards you could
>> connect the PSU to that as a dummy load. I don't think there is much 
>> in the
>> way of dependency on the CPU to run the PSU.
> At this stage I've got no idea if it's a SMPSU or a linear (I've not 
> popped the panel off)... I suppose if it's linear then it perhaps 
> doesn't even need a load to do its thing. If it's a switcher then I 
> expect it'll at least need something on +5V, and maybe +12V too 
> (unless it has built-in load resistors to keep the regulation happy, 
> as designs occasionally do).
Its a SMPS.  It must be loaded to work right and there are no loading 

FYI there ca be an ISSUE with the SMPS to backplane cable.  The correct 
part has equal
length wires.  The earlier version of the cable had unequal length wires 
and tended to
overheat some of the pins and fail.  Be aware.

> I see on the output rating label that it lists connection points for 
> different outputs, so maybe I just need to slap a couple of suitable 
> resistors onto the +5V and +12V outputs so that they draw an amp or 
> so, and see how it goes.
>> Once you have the machine up and running...
> Lets not get ahead of ourselves ;-)
>> I am not sure if 4MB is enough to do that though.
For MicroVMS its adequate but minimal.  Typical systems had 8 or 12MB 
though 16mb was possible.
For VMS 5 the DEQNA is fine if working, also you need 8mb to run well.  
With 12mb or more and a large disk (min RD54) VMS 6 or later is possible 
with DELQA (required after VMS5.4).

It will also run NetBSD (Myneed 8MB) and also Ultrix.

For disks....

RD53 is 31mb (maybe adequate for MicroVMS), RD53 is about 70MB, RD54 is 
The RD 54 is the biggest drive for the RQDX disk controller.  IF a CMD 
scsi controller
is in there then RZ scsi drives can be used and small started at about 
300mb and up.

> Hmm, one of the things that I'm clueless about right now is how the 
> bus evolved over the years - I've still got a pile of Q-bus boards 
> which I saved from a recycler last year, and I know there's a 4MB 
> board (made by Clearpoint, if I remember right) among them. But if 
> that's designed for earlier PDP hardware then it's possibly no use 
> whatsoever in a Vax world...
The correct board for MicroVAXII cpu has the over the top connector that 
lines up with the cpu
and needs a IDC 50 pin connector for CPU and each board, max of 3.

DO get the MicroVAX tech and user manual off bitsavers.  It will help 
greatly.   FYI many PDP11
board can be used to the limit of the backplane space the exception is 
memory as it must
be MicrovaxII  PMI (private memory bus interface).

FYI there are three possible cpus.  MicroVAX-I not much use as it very 
limited, MicroVAXII KA630
was the stock cpu and the later KA650 coule be installed.  All three use 
memory unique to that

Also learn the backplane as it has unique slots for CPU and memory and 
shuffling cards can
cause problems.

The panel on the back cover carries the console connector and the TOY 
(time of year) battery
backup (NICd) that do fail and leak.  Replace.

Also the default NI interface is AUI so an AUI too Either coax or Cat 3 
or 5 wire is needed.

Like I said get the book its a very interesting machine and if the disk 
has a valid and boot able
OS there is a specific procedure for lost system password.


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