[cctalk] Re: Another 780 backplane story

My backplane horror story isn't so fun. The old TOPS-20 had an 'emergency power off' button. I'm told that it would connect 5V to ground through the backplane for when you really, really didn't want someone to bring it back up easily. Seems like a really stupid feature, but the university I went to had a bunch of military connections, and it may have been for a contract with them (or maybe we got the machine surplus from them, I never could figure out the details). Anyway, in March we announced that we'd be switching the TOPS-20 machine off just before school started again in August. One of the tops-20 operators "accidentally" hit this switch just before finals week because they needed more time to finish their final... That didn't end well for them... We had a field service person rebuild the backplane, replacing the charred wires with fresh, and finding all the ones that had been too stressed out by the surge. They started in May and were done the last week of July. So we were able to runt the TOPS-20 machine again for 3 weeks before we shut it off (well, due to the failures, that extended to 5 weeks). So 10 weeks of field service time to get 5 more weeks of life from the machine... And even then, it was "brittle" and useful only for data extraction and transfer to the new Sun workstations... The power of stupidity... None of this billed out at $1600/hr, though it was the mid 80s. Warner On Fri, Jul 4, 2025 at 1:39 PM Mark Kahrs via cctalk <cctalk(a)classiccmp.org> wrote: