DEC PDP-8/e H212 core mat repair
rice43 at btinternet.com
Mon Jul 19 03:40:44 CDT 2021
------ Original Message ------
From: "Tom Hunter via cctalk" <cctalk at classiccmp.org>
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
Sent: Monday, 19 Jul, 2021 At 06:33
Subject: DEC PDP-8/e H212 core mat repair
I am curious if anyone has attempted to repair (replace) a broken wire
PDP-8/e H212 (MM8EJ) core mat (8 k word). The cores are not visible
a microscope. I cannot imagine how these were even manufactured and
if DEC service centers repaired core mat faults or if faulty boards were
CDC 6600 cores were huge in comparison and I would not hesitate to
a broken core wire on those.
I believe much of the core manufacturing for DEC minicomputers was
outsourced, but a lot of it had become much more automated by the late
60's and early 70's. I believe it was done by machine, with a tray to
hold the toroids in place, and a very fine needle-like "bobbin" that
threaded the wires through the toroids. I believe threading the cores by
hand had become largely obsolete by the time the PDP-8 came onto the
Though i can't confirm it, i highly doubt that DEC engineers would
repair core planes. These would more likely be sent back to the
manufacturer for "recycling", with the cores being recovered and reused.
It's worth noting that most computer manufacturers appreciated the
fragility of core memory planes at the time, with most of them being
protected with either PCB's or perspex/plastic shields on top of the
core planes. In this way, it was rather difficult for a clumsy ol'
technician to put his thumb through the planes as he was servicing
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