DEC PDP-8/e H212 core mat repair

steven at steven at
Mon Jul 19 02:59:59 CDT 2021

Tom said
> I am curious if anyone has attempted to repair (replace) a broken wire in a
> PDP-8/e H212 (MM8EJ) core mat (8 k word). The cores are not visible without
> a microscope. I cannot imagine how these were even manufactured and wonder
> if DEC service centers repaired core mat faults or if faulty boards were
> simply discarded.
> CDC 6600 cores were huge in comparison and I would not hesitate to replace
> a broken core wire on those.

I have no idea how DEC made theirs but for IBM's System 360, one of their engineers
came up with the clever idea of stretching the core wire so it necked and broke, leaving
a work-hardened tapered point to thread the cores with.
They patented it
(Source: page 187 of  'IBM's 360 and early 370 Systems' by Pugh et al)
On a Youtube film about the 360 they show cores being vibrated into the correct
orientation on a jig board.

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