MicroVAX 3300/3400

[Zane Healy]

> 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. :-)

https://www.zanesphotography.com/Private/MicroVAX/n-96z8NZ/MicroVAX <https://www.zanesphotography.com/Private/MicroVAX/n-96z8NZ/MicroVAX>

This is probably the best of the photo’s of the cabling.

https://www.zanesphotography.com/Private/MicroVAX/n-96z8NZ/MicroVAX/i-vFkfBQ2/A

> 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
> expander.

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 manual.

From the manual:
Slot 0 - M9715-AA Interface Module
Slot 1 - M7638-YA I/O Module
Slot 2 - CPU Module
Slots 3 - 6 - Memory Modules

My system:
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 place.

> 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.

Thanks,
Zane