DEC PDP-8/e H212 core mat repair

------ 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 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. Best regards Tom Hunter 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 market. 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 machines. Josh