Microvax II 'primer'?

Glen Slick glen.slick at gmail.com
Sun Jan 21 15:20:30 CST 2018

On Sun, Jan 21, 2018 at 11:25 AM, Jules Richardson via cctalk
<cctalk at classiccmp.org> wrote:
> So, I picked up (and I did just carry it into the house, and now I hurt) a
> Microvax II from another list member yesterday. Cosmetically it's a disaster
> (BA123 has a cracked top panel, broken wheels, missing front door, missing
> right-rear panel) but internally it appears to be complete; board wise we
> have:
>   M7606 - CPU
>   M7608 - 4MB ram
>   M9047 - grant continuity
>   M7504 - DEQNA ethernet
>   M3104 - DHV11 8-port serial
>   M7555 - RQDX3 disk controller
>   M7546 - TX50 controller
> ... it's got a TK50 and hard drive (no idea of capacity).

First thing I would do myself is remove the NiCad battery pack from
the back of the console connector bulkhead panel and inspect the
console panel PCB for any signs of corrosion. In my experience those
old NiCad battery packs can leak and start to destroy anything near

Note that the DB9 connector on the MicroVAX KA630 / 650 / 655 console
bulkhead panel is not the same as the usual PC standard.  For DEC
original cables you need a BCC08, or if you're doing MMJ cables an
H8571-B or an H8575-B MMJ adapter. Of course you can always build your
own cable.

Table 14-7 MicroVAX DB9 Pin-out

Table 14-8 DECconnect MMJ Connectors and Adapters

MP02071_630QB_Mar85.pdf  --  Maintenance Print Set
Page 85 of the PDF, Function Selection & SLU Module (FS&SLU) for M7608 (KA630)

AZ-GM3AA-MN_uVAXII_Maint_Oct85.pdf  --  MicroVAX Maintenance Guide
Page 23 of the PDF, page 1-15, FIGURE 1-10 Backplane Grant Continuity
If this is your first time with a BA123 it is important to note that
the right most slots 1 through 4 are Q22/CD slots. Don't put any dual
wide cards in the lower CD half of slots 1 through 4. The CPU should
always be in slot 1 and the first memory card in slot 2. If you have a
second memory card it would go in slot 3. If slot 3 or slot 4 would
otherwise be empty you need an M9047 grant continuity only in the top
AB half of the slots. If any AB or CD half of slots 5 through 12 would
otherwise be empty you need an M9047 grant continuity in each half
between the CPU and the last slot that is in use.

The M7606 KA630 CPU contains 1MB. Together with the M7608 4MB memory
board you then have 5MB total. I've never tried running a system with
that little memory. If you're actually going to do anything with the
system you might look for a cheap M7609 8MB memory board to use
instead for 9MB, or use both for 13MB if you have a 3-way memory bus

If it was me I might look for a cheap M7620 KA650 or M7625 KA655 CPU
and 1 to 3 M7622 16MB memory boards. Those CPUs can use up to 64MB but
you are limited to 3 memory boards in a BA123 because there are only 4
Q22/CD slots. I maxed out my own BA123 with an M7625 KA655 CPU and 2
Dataram 32MB memory boards to get to 64MB.


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