On May 25, 2021, at 3:50 PM, Glen Slick via cctalk
<cctalk at classiccmp.org> wrote:
On Tue, May 25, 2021 at 1:32 PM Zane Healy <healyzh at avanthar.com> wrote:
It turns out that the oddness was the CPU Board, and a 16MB Clearpoint RAM board. What
I thought was the CPU, is really the header panel over the RAM and TK70 controller. There
is also a M9715 between the CPU and the powersupply that I?d missed seeing. The cables to
get to the DSSI connector by the Powersupply are hanging out the front. Basically it?s a
cable going from the KA640 to a ribbon cable to a cab kit, then DSSI cable from that to
the connector next to the power supply.
Sounds like somewhat of a mongrel system. An M7624 KA640 CPU would
typically be found in a 12-slot BA213 as a MicroVAX 3400, or in a
smaller 6-slot BA215 as a MicroVAX 3300.
Except for the DSSI cable strangeness, it?s a really nice chassis. Though after a LOT of
reading in the last 24 hours, may are right on it being a mongrel. It also explains my
confusion as to what it is. :-)
This is probably the best of the photo?s of the cabling.
As far as I can tell a 12-slot B400X is essentially
exactly the same
thing as a BA430, where it is a BA430 when used as a VAX 4000-200 with
an M7626 KA660 CPU, and a B400X when used as a Q-bus and storage
Based on the BA430/BA440 manual, it looks like the main thing it?s missing from a BA430 is
the SCP with the ?Halt? and ?Restart? buttons (it has the temp and DC indicators), along
with the M7638-YA I/O Module. I?m trying to find a description of what the M7638-YA
module does. The only place where I seem to find mention of it is in the BA430/BA440
From the manual:
Slot 0 - M9715-AA Interface
Slot 1 - M7638-YA I/O Module
Slot 2 - CPU Module
Slots 3 - 6 - Memory Modules
Slot 0 - M9715-AA Interface Module
Slot 1 - KA640
Slot 2 - MS650 (16MB Clearpoint)
Slot 3 - M7559
Slot 4 - M9047
Slot 5 - M9047
Slot 6 - 12 - Empty
This might be a bit odd, but I don?t think this is a problem, I did try pulling the M7559.
Really the diagnostics seem to be indicating to me that I have a bad KA640 board
(specifically faults on at least a couple areas.
One question, do I need to worry about the batteries on the H3602-SA panel? I can?t
imagine that this would be causing any issue.
An interesting thing about the BA430 backplane is that
in addition to
the M7626 KA660 CPU DSSI bus being present on the 50-pin connector, it
is also present on the C/D connectors, and the BA430 backplane routes
the DSSI bus on slot 1 C/D connectors to the DSSI storage device bays
without the need for a DSSI cable.
I finally found that, in the ?KA660 CPU System Maintenance? manual. What?s interesting is
that there is also a 50-pin header on the KA660, and I?m not yet clear on why. :-)
If I remember correctly the DSSI bus is only present
on the 50-pin
connector of the M7624 KA640 CPU, not on the C/D connectors, so a DSSI
cable is needed with that CPU.
As near as I can tell this is correct. It also explains the strange cabling.
The hidden M9715 board in slot 0 between the CPU slot
1 and the power
supply provides termination power to the internal DSSI and SCSI buses
of the BA430 / B400X backplane. It also has a connector which routes
to the DSSI bus on the C/D connectors. In the BA430 nothing connects
to the M9715 connector as the DSSI bus should be coming from the M7626
KA660 CPU C/D connectors. In the B400X there should be an external
bulkhead DSSI connector with a ribbon cable to the M9715 connector. In
both the BA430 / B400X there should be another external DSSI connector
to the left of slot 12, which is the other end of the DSSI bus.
The DSSI bus goes into a cable on the upper left, that then goes to a connector on the
lower left, with the terminator. I?ve photo?s of both. I was interested to learn that
there is also SCSI cabling in there.
So it sounds like you have a B400X with the M9715
internally cabled to
the external bulkhead DSSI connector as usual, and the M7624 KA640 CPU
internally cabled to an external bulkhead DSSI connector, and then an
external DSSI cable between those two bulkhead connectors. If that is
basically how the DSSI things were cabled up, did you also have a DSSI
terminator on the bulkhead connector to the left of slot 12? Without
checking this myself with a M7624 KA640 CPU you probably get some sort
of errors somewhere if the end of the DSSI bus is not terminated.
As near as I can tell, I have the B400X config for the M9715, and the terminator is in
If you were to find an M7626 KA660 CPU you could do
away with all of
the DSSI cabling between the CPU and the M9715 (in addition to having
a CPU that is around twice as fast).
After determining that I don?t need new RAM, this is starting to have a real appeal. I
should also be able to take RAM from the MicroVAX 3, and further bump up the system, which
is good, as 16MB on a 4000/200 would be really tight.