Crazy Eddie's Used Computers
I went down to @icm to work on Miss Piggy, their PDP-11/70 system. Any instruction that touched memory would wedge the processor (though front panel accesses worked OK). Brought along my KM11 diagnostic set to help diagnose the issue and traced it down to a faulty microcode ROM (one of several early bipolar 256x4bit PROMs in the system). We had a spare ROM board so we swapped that in; chip-level diagnosis will happen at some later date. The system boots 7th ed. UNIX once again!
Mar 8 at 2:20amWeb
Show threadCrazy Eddie's Used ComputersMar 8
The 11/70 is a fun system to work on. The service documentation is excellent and you get to work thorough fun diagrams like the one below, which traces through all execution paths of the microcode (all 256 words of it). 14 such sheets cover the entire microcode, which implements the entire PDP-11 instruction set as well as front panel operations. (With a lot of help from the hardware, of course.). Each box in that diagram describes what a single microcode word does when executed.
Show thread☮ ♥ ♬ 🧑‍💻Mar 8
@fvzappa @icm what version of ThinkPad are you using (<= T30)? No trackpad, which in my view is good, unlike my T40.
Show threadCrazy Eddie's Used ComputersMar 8
@peterrenshaw @icm It's an X200s that I got out of a free pile at a local event a few years ago. Nothing fancy but it's small and it has the extended battery, which still works great!
Show threadKarl AuerbachMar 8

@fvzappa @icm I've got the console - and only the console - from one of my old PDP 11/70s. I used to have the boot address in the switches but somebody messed 'em up.

My fingers sort of vaguely remember the switch settings to boot Unix (we mostly used Interactive's IS/1), but they have forgotten the details and I'd like to put the switches back to what they ought to have been.

Show threadICMMar 9
@karlauerbach @fvzappa 165020
Show threadJan v/d BroekMar 8
@fvzappa @icm I love the blue switches.