@dc42 Yeah, that's it.

Now I can put a big red STOP button on the front of my machine: in the case that kittens, puppies, or tenured professors get stuck in the high-speed moving parts, the button cuts the power to the motors and they stop nearly instantly. Kittens everywhere are safer... perfect answer, thanks again!

There is a D20 on the 1HCL v2.0 board which is not on the 1HCL 1.0a schematic.

If I had a copy of the v2.0 schematic, would this D20 diode have a cathode on VB_FUSED and anode on the input filter ferrite bead to the 12V board power supply (parallel to D10 from V_FUSED)?

I'm wiring closed loop and really like the ability to deenergize the motors without losing the logic. Some of the 1HCL boards I bought (thank you KB-3D!) are v1.0a, so looking to OR-bridge the alt power to the logic with a cheap Schottky. This surely looks correct but I'll ask if anyone else has done this.

So, have ya?

So I spent a few hours over a couple of days trying to figure this problem out, then spent a day reading the internet to see if anyone else had it, followed by posting a description of the problem.

Within a day, I get one of the best answers I've gotten on any forum in the last ten years. So guess what happens when I go check the problem again?

Evil invisible dust bunny has fled. Computer acts like nothing was ever wrong. Thank you for the magic blue smoke engineer voodoo.

The 6HC and three 1HCL boards CAN bus links up within a second of booting. It all works perfectly and is a modest complement to my building skills (no comment on my cleaning skills).

"replacement under warranty" - that's what I was trying to avoid. I do not like returning goods to well-meaning manufacturers and frankly... returning open-source hardware is against my religion. Everything else about the Duet3D hardware/firmware/software is working perfectly by the docs. I'm very impressed!

Thank you again for the assistance, I have so many many questions.

Hey, thanks for the reply!

I haven't dug out my old network tester but all the cables I've made so far work fine when rotated around. Any of the 3 1HCLs that follow the affected one blink the status LED fast, any between the 6HC and the affected blink slow and show up in the list on the machine-specific config web page.

I might be hallucinating. All of the solder joints look really good, nice processing. I'ma do all the tests again, yeah, it seems like I must be missing something easier.

I'm daisy chaining the CAN bus on a set of 3 1HCL expansion boards off a 6HC main board. One of the 1HCL's has a bad exit CAN bus RJ-11 port, and won't send. I've switched cables around, it's not a bad cable, it's not the termination jumpers, I measure zero ohms between the gold wires on the (same position) tops of the connectors, and I've looked at the schematic and verified everything I can see that isn't covered up by the connector bodies. It's either a very very determined invisible chunk of dust sitting on the inside of the connector or something sneaky I'm not seeing yet.

I don't seem to find any trouble exactly like this mentioned in the forums here. Before I clean off my desk and set up an oscilloscope, is there anything obvious I forgot to look for (other than trying to file the inside of the connector) ? Maybe this doesn't happen very often and I'm lucky? I'm thinking I'll make a special cable with a short tap on it for that particular 1HCL board.