@dc42
Seems like this is it. I have another supply, 24 V, 14.6 Amps, so I hooked that up. Same result, except the power supply keeps resetting so the LED flashes every few seconds.
I tried unplugging all steppers, same result. I fear I may have fried something important.
Bingo! 2.7 volts out from PSU when connected to the board. Thanks! I'll replace the
PSU ASAP.
I've upgraded my Ender 3 Pro to use the Duet 2 Maestro board (which I love, btw), and everything has been chugging along fine, I've printed roughly a Kg of PETG, and was switching to PLA. I switched off the power, leveled the bed by hand, switched power back on, loaded some bed level checking gcode, and walked away while the bed was heating. I came back to find the web interface telling me it's lost contact with the board, and no lights on the board.
Things I've checked so far: Power supply is fine, outputs 24 volts as expected. I haven't tried it under load, so maybe there's something that only shows up when drawing current, but that seems unlikely. Power supply fuse is good. Turning on the power makes the Vin LED flash briefly, but that's all. It seems to have died completely. The only thing I can think of is that in moving the hot end around by hand during the leveling process I generated power through the steppers that fried the board, but I've done this at least 20 times, and it was OK at first when I turned it back on - only after I started the process of heating the bed did it die.
I have a good multimeter but before I go poking around I wanted to see if there's anyone whose run into this or any suggestions about what might be going on and how to fix it. I really like the board so far, so I'd very much like to revive it.