PDP 11/70: MK11 memory crate, M9312 cards, and wiring...

From: Jules Richardson <julesrichardsonuk_at_yahoo.co.uk>
Date: Sat Oct 9 12:50:54 2004

Hi all,

We've got an M9312 boot / terminator board in our Decsystem 570 (which
has 11/70 internals). The board has four spade connection points on it -
TP1 - TP4. Now, TP1 has a couple of wires connected to it, one white and
one clear, and TP2 has a black wire connected to it. These appear to run
up to the central pillar of the rack - I expect to the 'initialize'
switch. (TP1 is boot input, with TP2 as return, whilst TP4 is enable
boot with TP3 as return)

TP3 and TP4 are currently unconnected. *However*, we have a crate of
memory in the machine in a box labelled MK11-C2. From this there's a
cable dangling out the back, with a pair of spade connectors at the end
(one spade having both white and black wires running to it, the other
having clear).

I suspect this is supposed to plug into TP3 and TP4 on the M9312 board,
but can anyone confirm this? What does the cable actually do? I'm
guessing it's some sort of 'power good' type of signal back to the

And whilst I'm here...

We have three H775D battery modules for the machine. The back of the
MK11-C2 has an 8 pin connector marked as being for such a battery unit -
anyone know if the cable's a straight through between the memory crate
and the battery unit? (i.e. 1-1, 2-2 etc.)

I suspect the other two battery units were spares - but the MK11 also
has two more unlabelled 8 pin connectors; are these important for
anything? Will the memory unit be happy without any battery unit(s)
plugged in?

Also... :-) What do J1 and J2 do on the back of the MK11? Currently
pins 1-3 on J2 are shorted via a small plug, whilst J1 has nothing
connected to it.

As mentioned in a previous email, the machine power supplies look good,
but whilst various LED's on the CPU front panel are lit, with the key
inserted we're still unable to use any front panel switches to yield any
signs of life. My *guess* is that the cable hanging out of the memory
crate should be plugged into the M9312, and the system isn't starting
because it thinks the memory crate is upset - but I could be totally
wrong on that and something else is up with the CPU...

And if anyone has any answers in the next 12 hours, then great - as I
can spend all day tomorrow screwing around with the machine then :-)


Received on Sat Oct 09 2004 - 12:50:54 BST

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