VAX 4000/105A Basics: The VAX 4000/105A is one of the mightier VAXen. At 32 VUP it's no slouch and it's maximum memory size of 128MB is very nice for running the most current versions of OpenVMS. The other nice thing about this machine is it's got more busses than Greyhound. I have yet to identify them all, but it has several DSSI busses (4 me thinks), at least one SCSI bus, a QBus and many other bus plugs all over the motherboard. This is a MicroVAX and not a VAXstation so it doesn't have a video card, mouse or keyboard. At some point DEC dropped the "Micro" from "MicroVAX" and just started calling them VAXes. They're hard to find units. The Marmotking had to pay WAY too much for this one. They consistantly sell for high sums on our *favorite* auction site. When this one showed up on my doorstep, it was in fairly bad cosmetic shape. However with a lot of scrubbing (Simple Green is your friend) and replacement of doors and such from a dead 3100/40, it's now not such a bad looking machine. Here's a photo of the rear of the machine. It's got this cureous wart hanging off the back with all the various busses exposed. Not the most elegant looking solution.
The status LEDs mainly show POST information. I haven't found them very useful. You'll have to consult the 105A manual for more information. The reset switch is more of a "Halt" switch, I beleive. It takes you to a BIOS prompt where you can do all sorts of things like format hard drives, reboot the machine, change the boot device, run self tests, etc. I usually do a shutdown of VMS and then press this button after the OS has stopped. When you get a new machine, you may need to use this button to get out of a failed boot. There are four serial ports on this critter. Three of the ports look like RJ-45s, but don't be fooled! They're special DEC connectors called MMJ connectors (note the offset spot for the tounge). They also aren't exactly RS-232, since they use a voltage differential scheme rather than a reference ground. However, the implemention is such that it's RS-232 compatible. MMJ cables and adaptors are readily available to convert to DB-9 or DB-25 connectors. You can see that the remaining serial port is a standard DB-25 connector. I think this is DTE standard signaling. The important point here is that you must connect a terminal to the "port 3" MMJ connector first. This is the "operator's" terminal and the only one you can use to boot the system. You can connect other terminals and printers to the other serial ports as needed. Also note the "Break Enable" switch. This has something to do with whether a "break" signal is accepted from the terminal. Unlike the 3100 series of MicroVAXen, enabling or disabling this switch doesn't appear to change which port is the console port. I haven't had time to research this switch any further. Like most of the MicroVAX and VAXstation machines, this machine has two network plugs. Only one is active at a time and it's selectable using the switch that's between them on the back of the machine. The BNC connector is a standard Thinnet coax connector. The D-connector is an AUI plug and requires a transceiver to use it with an RJ-45 twisted pair cable. The SCSI connector is self-explanitory. It's your standard 50-pin, Centronix connector. Note that the internal SCSI controller occupies SCSI ID 6 and don't forget to terminate the external end of the bus. You can connect SCSI CD-ROM drives, DLT tape drives, hard drives, etc. to this connector. It turns out that internal hard drives (as you'll see in the photos below) are really intended to be DSSI drives. There's an interal SCSI bus which could be used for hard drives, but the cables are only accessable to the CD-ROM/Floppy drive bays. But one can get creative and make new cables to route differently and in mounting the internal drives. Lastly, before we dig into the internals of the machine, it's worth noting the presence of three DSSI connectors and two QBus connectors. I know next to nothing about DSSI, other than the drives are really smart. They contain several programs on-drive which can be run through the VAX BIOS prompt. There are two busses exposed here on the back. The right most two connectors are the two ends of one bus, while the left connector is on end of another bus. I'm not quite sure yet how these relate to the internal DSSI connectors. However, if you view my "Fireup Notes" you'll see that leaving these unterminated causes issues. As for the QBus, I'm Sgt. Schultz. I believe there's an external QBus enclosure you need. I'll post more later if I run across such a beasty. BTW, the DSSI terminator looks like this:
Now, into the belly of the beast.
As you can see there are three DSSI headers available for mounting hard drives on the top shelf. Special DEC mounting brackets are required, unless you want to get creative. Here's a photo of a DSSI drive with attached mounting bracket. The screws then fit into the holes on the shelf and the whole thing locks into place with the three spring-loaded tabs at the front.
More to come... Useful Resources
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