One step forward, multiple steps back.

The good news: after 7 months I finally got the metal hot-ends for my printrbot metal plus. The bad news: I need a new printrboard. The irrelevant news: I think I’ve discovered a  failure mode for printrbot’s extruder board that could be useful for other dual-extruder folks to know.

So yeah, after various and sundry delays, the hot-ends that only an optimistic fool would have expected to actually ship with the machines last winter appeared in my mailbox. And now that the kids are bad in school I had the attention span to install them. Pretty straightforward, although the instructions for the hot-end fans appeared not to work for me (attaching first fan ground to ICSP ground: fine; attaching second fan ground to I2C ground as shown in picture, printer and entire usb bus lock up). So I found a ground somewhere else, and everything worked, so it was time to recalibrate the Z offset.

Except: apparently my X limit switch had gone south, so the machine racketed itself into the stop for a 30 seconds each time, and only then tried to home in Y and Z.  So I took a look at that, and found (apparently) that my habit of laying the machine down on its side to take off the bottom had caused the carriage or maybe some stray wire bundle to mash the limit switch flat so it no longer registered. Pulling the spring back out fixed that.

But then: Z homing no longer worked. The carriage moved up a bit and the software announced that the end stop had triggered even though the inductive sensor wasn’t seeing anything. A few searches yielded some very long threads on exactly this problem, with recommendations to see whether the stop remained triggered when the sensor was unplugged — in which case a toasted FET was likely the problem — and to check voltages on the endstop pins to make sure. So I unplugged the sensor: yep, endstop still triggered. I reached in with my multimeter probe to check voltage: ZOT! out came the magic smoke from some component on the board, doesn’t really matter which one. I can console myself that something irreparable was almost certainly already wrong, but it’s still an annoying mistake.

Oh, and if you have a dual-extruder setup with an extruderboard, exercise caution when doing things that might cause your printrboard to hang, crash or otherwise stop working. When my main board was wedged (see I2C ground, above), the temperature of the hot end plugged into the extruder board took off for the stratosphere each time. Luckily, I had a finger nearby and noticed. As soon as everything was operating (somewhat) normally the hot end behaved fine.

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