PDP-8 core memory problems.

Jon Elson elson at pico-systems.com
Mon Sep 5 16:21:27 CDT 2016

On 09/05/2016 01:59 PM, Mattis Lind wrote:
> I have now concluded that the fault is in the core memory module itself.
> The sense winding is broken on bit plane 7.
Have you actually ohmed out the sense/inhibit wire?  There 
were some very old memories that had some kind of 
metallurgical problem where the wires corroded away, but not 
heard of DEC cores being prone to that.
3D core stacks have combined sense/inhibit wires, and there 
is usually a pulse transformer between the sense amp/inhibit 
driver and the wire itself.  Also, if the bit 7 inhibit 
driver has a blown transistor, it could cause the sense amp 
to be shunted or overloaded.  I'd check all the associated 
sense/inhibit circuitry before assuming it is the plane.  
(Of course, you may have already done all this by swapping 
boards, etc.)  A blown inhibit driver could take out the 
pulse transformer, too.


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