PDP-8 core memory problems.

[Jon Elson]

On 09/05/2016 05:26 PM, Mattis Lind wrote:
> måndag 5 september 2016 skrev Jon Elson <elson at pico-systems.com>:
>
>> 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?
>
> Yes. I have measured at at the tabs where the red arrow points in the image
> below:
>
> http://i.imgur.com/x5VVh2F.jpg
>
> Unfortunately I am pretty sure that this will rule out pulse transformers
> or whatever.
>
>
Ugh!  That could be messy.  DEC later went to planar 
memories, for obvious reasons.  Yes, these built-up core 
stacks could be hard just to open up to get to a single 
plane.  IBM, CDC and others all made them like this in the 
60's before realizing how hard that made the job of testing 
and repairing.  (I guess the shrinking of the cores is what 
really made the planar core boards practical.)  Well, unless 
there is a spare plane in the stack, you can't break it too 
much more than it is broken now!  But, really, if one of the 
wires has failed within the plane, it could be just about 
impossible to fix. If it is a break outside of the core 
matrix, that wouldn't be hard to fix, unless the wires have 
become brittle over time, in which case any manipulation 
would just cause more damage.  GOOD LUCK!

Jon

Jon