PDP-11 Memory

[Bill Gunshannon]

On 1/12/19 9:20 AM, Bill Gunshannon via cctalk wrote:
> 
> 
> Well, the problem is definitely bus grant as with just two memory
> cards in the machine I put the disk controller in and it does not
> show up in the Map.  The only problem with this is the question
> Why?  I  have examined the memory cards.  The C-D (actually, C)
> does have the bus grant lines connected.  I even looked under a
> magnifier to be sure the trace hadn't been cut and it is intact.
> So, what else cold cause this?
> 
> (Another question, however, some cards have the ability to open
> this.  Why would you ever do that as it would break pretty much
> any card that followed?)

Problem fixed.  Note, fixed, not solved.

I dug out another MicroPDP BA23 box.  Stuck the CPU in slot 1.
Started adding the memory cards one at a time and turning the
machine on  waiting for the self-test and then doing a MAP.
Worked perfectly.  The self test got slower as each memory
card was added and the map showed the block of memory and the
assigned CSR.

So, what could go bad on a backplane to cause this problem?
Or, could it be a power supply that is no longer delivering
the rated power?

In any event, I, at least now, have two functional systems.
an 11/93 with 2 meg of memory (which might be expandable
with PMI but definitely not with QBUS memory.)  And an
11/73 with 4 meg of QBUS memory which apparently could be
an 11/83 if I had 4 meg of PMI memory.

Anybody got any PMI memory they would be willing to let go? :-)

bill