On Tue, May 25, 2021 at 1:32 PM Zane Healy <[email protected]> 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. 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. 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. 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. 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. 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. 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).
