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Dumb memory compatibility question

    Date: Fri, 19 Oct 90  16:28:36 EDT
    From: delaney@xn.ll.mit.edu (John R. Delaney)

    Among which 36XX models are memory baords interchangeable?

All (Yes, all.  See Below)

    In particular, could boards fromm a 3640 or a 3645 go in a 3670?


    Thanks in advance,

    John (the cannibal)

Some people may not realize that with a little modification, you can
even put SLB memory boards into 3640s.  I've sucessfully used 1mw
SLB boards in a 3640.  I won't make any claims for the other OBS models,
but as far as I know they are really all the same.

Below tells you how to put an SLB into a 3640.  [I know this is not what
you want to do, but I'll bet that someone out there wants to do it, and
it is certainly part of the memory compatibility issue.]

could destroy a memory board or, even worse, destroy a backplane.

The SLB boards do not fit into 3640s until you perform surgery on the
structure of the card cage in the back of the machine.  You have to
either remove or modify the board guide that runs between the upper and
lower pairs of pin sets on the backplane.  It is better to remove the
piece and use a hacksaw to cut the appropriate gaps in it and then
replace the piece in the machine so that you can slip the board in place
while the guide still is able to hold the lower boards.  After this
step, you ought to place a pin guide over the pins for the slot that you
want to add the memory.  You will probably find pin guides in the lower
portion that can be removed and placed in the upper portion.  It's that
black plastic part that fits over the pins.  You need these pin guides
to reduce your chances of breaking or bending a pin on your backplane.
After you have the room to insert an SLB into a slot on the top part of
the cage and have the pin guide properly inserted, you may carefully
insert an SLB memory board into that slot.  When you power up the
machine, the FEP will be happy to recognize the board without you doing
anything special.

Important notes:

Do NOT put an SLB memory card into the bottom portion of the card cage.
The voltages are different down there, and you could fry the board.

Do NOT bend or break a pin off your backplane.  You could destroy the
backplane.  This is a costly and tedious repair that no one wants to do.