11/73 into 11/03 chassis?

Jerome H. Fine jhfinedp3k at compsys.to
Mon Feb 8 19:45:04 CST 2016

I top post only once or twice a year.  This is the exception since my reply
does not explicitly address the question.

An internal built-in power supply is just the ordinary standard power
supply which provides power to the board on which the CPU is

I have managed to avoid many of the problems associated with power
supplies by using the built-in power supply only for the BA23 boards,
tape drives and, if any, floppy drives.

Note that when I use a TK70 tape drive in a BA23 box, it functions
correctly ONLY when connected to the built-in power supply.

Specifically, I always use a SEPARATE PC power supply for the hard
disk drives.  This is probably essential when I use THREE Hitachi ESDI
hard disk drives since their power requirements, when added to the
rest of the load, really challenge the BA23 box built-in power supply.
But I believe it is probably best even when just an RD51 is used
although the load from a single RD51 is probably OK to run using the
built-in power supply of the BA23.

In addition, the Hitachi ESDI hard drives also require an external fan
to keep them at a reasonable temperature.  The fans are also powered
by the separate PC power supply.

This procedure also works well with other systems, so I recommend
it to reduce the load and keep internal built-in power supplies from
being overloaded on any system, especially when there is more than
one hard drive.

Jerome Fine

 >Jacob Ritorto wrote:

>This is extremely good info (thank you to Robert, Joseph and Noel!) and I
>plan to do something like this someday when I get more q-bus stuff, but I
>must apoligise for my inaccuracy because what I was originally trying to
>ask was:
>Can I tear apart my little BA23 (which currently has a power supply problem
>and not enough space for my high capacity 8" SMD disks) and put the
>Micro/PDP-11 backplane (with all its nice 11/73 cards and SMD disk
>controllers, etc.) into the spot that my 11/03 backplane currently occupies
>and run it via the (working) stock 11/03 power supply?  This "11/03
>chassis" is bolted into what appears to be a common, official Digital 19"
>rack surrounded by some RL02s, mid-height style (don't know the name of
>this racking option).
>  Specifically, would I have to butcher power and clock lines to do this,
>or is it all plug compatible?  I'm considering tearing the systems down and
>assessing the situation, but wanted to ask in advance in case somebody's
>already gone there and can save me the heartache.  The recent mention of
>the dual 11/73 in a 19" rack prompted me to reconsider my original intent
>instead of rewiring old backplanes to be 22-bit compliant.
>>On Fri, Dec 11, 2015 at 8:19 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
>>    > From: Jacob Ritorto
>>    > Would you happen to have notes or references about how to do it?
>>It's not too hard; basically, one has to wire pins BC1, BD1, BE1 and BF1
>>(BDAL 18-BDAL21, respectively) on all _QBUS_ slots together into a bus. So
>>wire BC1 on slot 1 to BC1 on slot 2, slot 3, etc, etc.
>>A couple of notes: First, I said '_QBUS_' because if you have a Q/CD
>>backplane, clearly one doesn't run the extra BDAL lines to the CD slots,
>>the QBUS slots (which run down the left-hand side, when facing the
>>Second, for optimal analog behaviour, the 'out' slot on the backplane
>>be the last slot you wire to, so that there are no branches in the
>>transmission line for BDAL18-BDAL21 (which can produce reflections - aka
>>noise - on the transmission lines). How to do this efficiently (in terms of
>>the wiring) can be a bit tricky, depending on the backplane configuration.
>>E.g. if one has the standard 'serpentine' backplane, i.e. one with the
>>in the following kind of order (facing the backplane from the board side):
>>etc., one might naively think one has to run the extra bus lines back and
>>forth to match. However, only the _grant_ lines have to follow this pattern
>>(and they are already there); the added lines don't have to follow the same
>>pattern, as long as there are no branches.
>>So, for the example 5-slot backplane above, one could/would wire:
>>i.e. a single vertical run on the left hand side, a single diagonal from 9
>>back to 2 (shown with "--"), and then another vertical run on the right
>>side. Much simpler than wiring back and forth in slot order; there are no
>>branches; and the last slot is the 'out' slot.
>>For backplane with an _even_ number of layers, e.g.:
>>it's a little more complicated: a single vertical run on each side
>>cannot be connected in such a way as to have the 'out' slot (8) be the
>>last slot. One has to do something a little more complex:
>>with a vertical run on the left side, stopping short of the last slot; then
>>a vertical run on the right side, then a lateral back across on the last
>>Obviously one _could_ run the wires back and forth, in slot order, but that
>>will take a lot more wire, which at the very least is more work (especially
>>on backplanes which don't have full wire-wrap pins, just the little stubby
>>pins that have to have the wires soldered to); whether it also increases
>>delay down those transmission lines enough to be noticeable is something I
>>don't know the answer to.
>>All the obvious caveats apply: make sure not to get confused by the mirror
>>pin and slot numbers on the front and back sides (you'll be wiring on the
>>back, whereas the diagrams above are on the front), etc.
>>        Noel

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