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Anatomy of a VAX 6000-420

Copyright © 2001 Gunther Schadow. All rights reserved.


Using This Document

This document countains numerous thumbnail images. Click on them to go to a 640x480 image. If you need to see more detail, manually change the URL for that image from "small" to "large". For example, if you click on the first URL you will see the URL: "some/thing/small/DSCN0001" now you can change this URL to "some/thing/large/DSCN0001" and see the larger image. I do this to save you some bandwidth when looking at this using a modem.


I recently saved 4 VAX 6000-420 from the junkyard. One of them, her name was "VAX1" had some power supply problems that made her shut down the minute she was booted. So, I decided to take her apart saving all the pieces as spare parts.

Gregg Economou (alias Lord Isildur) who had taken a similar machine apart for the purpose of putting it back together had forgotten to document how all the bits and pieces are wired together. This led me to produce this series of pictures that guide through a somewhat systematic dissassemblage of the VAX.


Since we're talking anatomy here we will use anatomic designation of locations.

When I say "left" and "right" in an image, I mean it relative to the machines point of view. When you look at the machine from the front, then the left side of the machine is at the right side of the image. You can get over the confusion by imagining shaking her hands, which side would you reach at? That's her right side.

Below is a glossary of other locational terms used in VAXian anatomy.

cranial: above (lat: cranium = head)

caudal: below (lat: cauda = tail)

superficial: outer, close to the surface

profound: deeper, closer to the center

ventral: towards the front (lat: venter = belly)

dorsal: towards the back (lat: dorsum = back)

Going to Work

The picture to the left shows the front of the machine after opening the front door. Everything is still intact. On the right is the same machine from the back, after taking out all electr(on)ic pieces (except for 3 functional wires, and some ground wires.) The central round structure is the blower. Cranial to the blower are the card cages (covered by plexiglass windows that shut off power when you open them.) The right card cage holds two VAXBI busses. The left card cage holds the XMI bus. Cranial to the card cages are the TK70 tape drive and the power regulators. There are three power regulator systems, two for the XMI bus and one for the VAXBI bus. The picture on the right shows some of those power units in the foreground.

The left picture gives a view on the XMI bus backplane. The long gray ribbon cable connected to the very right side of the XMI backplane is routed to the control panel board (not shown here, but see below). Most of the device connectors on the back of the XMI bus are unused here because the XMI bus only holds CPUs and RAM in this system. Note that there are a few XMI peripheral device adapter cards, e.g. the DSSI adapter, an ethernet adapter. However, With up to 6 CPUs and 8 memory cards, the XMI bus tends to be crowded with core system modules, so you don't whant to stuff it full with device adapters that could just as well go on the VAXBI bus.

The system of white textured ribbon cables on the right of the XMI bus links the XMI bus with the VAXBI bus. There are two XMI TO VAXBI adapter cards in the XMI card cage on the left. Each adapter card connects to one VAXBI bus by four of these ribbon cables. The short cables connect to the lef VAXBI bus, the long ones connect to the right VAXBI bus.

The right picture shows the backplanes of the two VAXBI busses. The VAXBI backplanes hold most of the device adapter cards. On the left you see said textured ribbon cables linking up to the XMI bus. On the left of the right VAXBI bus you see those same cables. You also see a gray ribbon cable linking between both VAXBI busses.

On the left VAXBI bus, just next to the XMI TO VAXBI card there is the CI interface adapter, which consists of two cards. You see four black cables with the yellow ring labels. We will follow those cables below. The gray thing cranial to the CI connectors that looks like some box is actually a set of short ribbon cables linking between the two CI cards. Note that this is only one CI interface but it consists of two cards and has 4 connectors.

Skipping over two empty VAXBI slots we see the TXB70 tape adapter with the light gray cable that is routed to the right cranial of the VAXBI cage, where the tape drive is located.

My right VAXBI cage only contains the VAXBI TO XMI adapter card on the left most side and the Ethernet card on the right most side. The Ethernet connector on the backplane is confusing. You see two cables going off of this connector, one round gray cable and another slightly thinner black cable. The gray one is the actual AUI Ethernet cable. The black cable connects to the corresponding VAXBI DC power regulator (detail shown below.)

These two pictures detail the power supply wiring to and from the XMI bus. There isn't much to say other than that it would seem to be extremely critical to get those power cables hooked up right. But if it was taken apart carefully, you will still have the power connector attached to the XMI backplane. You should have only removed the efferent wires connecting to the contol panel etc. These go off from the right side of the XMI backplane.

This series of three pictures details the CI connector hookup. The external CI connectors are the four BNC like things you see in the foreground of the left picture (a little out of focus, sorry for that.) These connectors are labeled A and B and T and R, which is seen on these yellow ring lables TA, TB, RA, and RB. In the right picture I have removed the internal connectors already and holding the CI cables so you can see these yellow ring labels. The connectors are plugged into the XMI backplane just left to the terminators you still see on their socket.

Here I show you the routing of the tape drive connectors. First you see the connector to the VAXBI backplane (where the TKB70 card is located.) This cable is routed up to the back of the tape drive. The tape drive actually sits in is own cage, so we see the back of that cage. The circuit board you see is the control panel board. For the right most picture I have disconnected the tape cable from the XMI backplane showing that connector in the foreground (again a bit blurry.)

These pictures give an overview of the wiring on the back. I have unfastened most of the cables from the clips that hold them to the walls, so you can better see the routing of these cables. (If you find this confusing, don't forget you can get the large image for better detail.) The ribbon cables running vertically are mostly power cables between the AC transformer unit on the bottom and the DC power regulator units on the top. I show most of these wires in detail below if not already shown.

The left picture shows how the Ethernet cable and the console cable are attached on the backside. We will follow the route of these two lines here. On the right picture you see the serial cable. A big D-25 connector that only has GND, TX and RX lines (no hard flow control or anything.) You see this round gray cable that connects to the control panel circuit.

Here is the detail of the Ethernet cable. Because it's a bit confusing, first we look at the back of the VAXBI again. The Ethernet sits on the very right of the right VAXBI bus. In the lower corner you see the connector with two cables. Just left to this connector is a terminator plug. In the right picture I try to show you the three (!) ends of this Ethernet line. You see a female D-15 AUI connector and the connector to the VAXBI bus. This thinner black cable connects to the DC power regulator unit shown in the background. I frankly don't remember why I am also trying to show you this small gray ribbon cable, but I do know it is not the same line I'm showing you next.

This gray ribbon seems to be the main power control cable. It would seem that it connects to a relais in the AC power supply unit. Even though the right picture is blur, it probably shows in enough detail that this power control cable connects in the most ventral slot of this AC unit.


Here I follow this long gray ribbon from end to end that connects the XMI bus to the control panel circuit. On the two right pictures you see my hand disconnecting the last connectors of this control panel circuit. This one leads to the tape drive again. This is consistent with the fact that the control panel controls system power, operation status and tape status. The last connector is just two little lines that run into the tape house. Where does it go? (See here.)

This series shows how I remove much of the power wiring. First you see another overview of those ribbons running vertically between the caudal AC power unit and the cranial DC power regulator units. Get to the large image to see better detail of which cable plugs into which port. Once the wider ribbons (that split up at the cranial end) have been removed, I remove the smaller ribbon, that runs between the DC power units' sub-units. The pictures on the right show me unplugging the XMI bus power connector. I did not try to disconnect every single wire from the XMI bus, but I guess from these pictures one could reconstruct this.

On the left you see the huge ground wires screwed to the back of the DC regulator boxes. You also see those small red and black wires that I don't remember where they lead to. The three pictures to the right show the connection of the heat sensor. I think there were actually two such sensors, one measuring heat and the other measuring airflow. These cause the power to shut down when heat gets too high or airflow ceases.

Here you have these pictures showing the disconnection of the XMI to VAXBI ribbon cables. These are 18 connectors in total but it's all pretty straight forward. No twisting, no crossing over. So these three pictures should give enough guidance.

Now let's turn to the ventral side of the machine. You see the DC regulator units again. The wires plugged in from this side lead down to the AC power unit again (as far as I remember.) To the right of the DC regulator units is the TK70 tape drive housing. Lightly bending the snap lets you slide the tape drive easyly out of its housing. On the back of the drive you see the gray ribbon and the power line, pretty much what anyone would expect who has ever opened a PC.

Here you see the empty tape housing. Another little circuit board hides in here. At the right inner wall you see how this ribbon cable is secured with a thick sheet metal. This is the kind of mechanics that you won't see anymore in today's machines. Fortunately this tape housing is just large enough to be able to unfasten those screws. The right picture shows the back side again. The control panel circuit is removed. In the foreground you see those gray and brown wires again. These are, I think, the ones that I pulled from the front of the DC regulator units to the back. This picture also begins to trace a four wire plexus that goes into the tape housing (indeed, this is the tape's power supply) and down to the power panel of the XMI backplane, as we shall see next.

Here again is the XMI backplane. This time we want to see the detail of those few wires we've begun following from the tape housing down. You see it coming into the picture from the right side. Red, brown, orange, and black. Note also that I have disconnected the long XMI TO VAXBI ribbon cables that run to the right VAXBI bus, but the short cables to the left VAXBI bus are still in place.

Another front view into the empty tape housing. The last thing I expected to find here is this funny little NiCd battery pack. This connected to the control panel circuit board. Next you see some of the last power wires running vertically. These are the gray-brown wire pairs again. I can't remember what exactly this other brown and yellow wire pair is. I think it is that second sensor (remember one was temperature the other was for airflow.) On the right picture you see about where all those colorful power-related wires connect to the front of the AC power unit. I don't know what those wires are, but from the combination of colour and plugs one should be able to reconstruct.

Notice the one pair that plugs into the blower unit, we will now follow this one to the back. This wire pair runs dorsal to about the center of the enclosure just cranial of the blower unit. There is a tunnel just large enough so I can get my arm in and loosen this wire. You can see it coming out of the tunnel to the back and into the blower unit. Getting this wire out through the tunnel wasn't easy but not impossible thanks to the spacious design. Now I could pull this wire pair to the front and out completely.

Again a look at the back of the VAXBI bus system. The point of this is to see the last wiring to the AC power unit. All the XMI to VAXBI ribbons are removed now. You can also see the large connector that connect the VAXBI's power plexus to the DC regulator unit. On the next picture you see something unexpected. Just right to the CI A to CI B card bridge (very short gray ribbon cables that look like a box) there is another cable. This is just three or four gray wires connecting to the VAXBI bus adapter. On the right picture I finally disconnect this short CI A to CI B bridge. Now I could take out both empty card cages.

I've got almost all of the wiring out by now. I took out all the DC regulator units, which you can see on the floor in the foreground. The housings for those DC regulators are empty now. The remaining red connectors are the interlock connectors, i.e., the interlock mechanism that turns off power to the card cage when the door is opened. I did not bother getting those connectors out as they were snapped in tightly.

A last look at the front of those lower AC power units. The last two wire harnesses unplugged. And out go those power supply units. On the right picture you see all those power units on the floor. We know there is one failure in this system of power units, but we don't know exactly what is wrong. So, I think that 6/7 of this is still in good shape. On the right margin of the picture you also look at the top of the VAXBI card cage. behind it you see the two card cage doors.

My work is done. Everything is taken out (except for a very few cables.) All is put in boxes and ready to take home. On the right you see three VAXen put nicely side by side. As you can see, the left cabinet ("Node 14") is the one that I just disassembled. Two days later Brian and I took the others (plus one that can't be seen here) home. Finally you see me on a picture taken with the timer, probably not the best perspective though.

Copyright © 2001 Gunther Schadow. All rights reserved.

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