How did I kill my Duet?

This is my Duet 0.8.5 and it just died a smokey death, but I don't know how.
The printer was on and I'd just used it to heat up and do the nozzle hot tightening on an E3d Volcano, I'd then disconnected the hot end and was fitting it to the effector when I heard a crackling noise and the Duet let out it's magic smoke
Link to image
Based on the photo does anyone have any idea how I killed it?
In hindsight I clearly should have switched it off but since there wasn't a hot end plugged in and it was doing anything I thought it'd be okay.

I'm sorry for your misfortune. L7 is completely burned out and the SAM processor has a hole in it. This strongly suggests that you had a short between 12/24V and analog ground. For example, a short between one of your heater wires and the ground side of the thermistor connection.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

After some thought I think it must have been a short between the +5v I use for the always-on cooling fan connector and, as you say, the ground on the thermistor connector. I got the idea to use dupont connectors so I can easily swap between a V6 and a Volcano from Tom on Youtube. I chose to use female connectors at the hotend end of the cables like he did, clearly this was a bad idea as the male connectors they connect to are live and can touch each other. A costly mistake!
Oh well, back to the Duet V0.6.

That sounds possible. The 5V regulator can supply 2A, which is enough to burn out L7 and then the SAM processor.

On the Duet WiFi there is no L7 and we have added a fuse in the VSSA line, which we hope will protect the SAM processor against this kind of short - but we haven't risked testing it yet.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

That sounds good.

Quote
dc42
we haven't risked testing it yet.

I'm sure some idiot like me will 'test' it for you soon enough

A similar thing happened to me. I was trimming the end of a cable sock with a cutter and accidentally touched its metal part against two exposed parts of the connector on TP3P's hotend PCB. I never saw any smoke, but the Duet died and I have the same kind of burn mark on the processor. This also seemed to have the effect of turning both heaters constantly on and I could hear the filament bubbling on my hotend. Yikes.

Quote
asbo
That sounds good.

Quote
dc42
we haven't risked testing it yet.

I'm sure some idiot like me will 'test' it for you soon enough

It's just been "tested" in the field. The fuse in the Duet WiFi blew and protected the processor as we expected it would. See [www.duet3d.com].

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
tomasf
A similar thing happened to me. I was trimming the end of a cable sock with a cutter and accidentally touched its metal part against two exposed parts of the connector on TP3P's hotend PCB. I never saw any smoke, but the Duet died and I have the same kind of burn mark on the processor. This also seemed to have the effect of turning both heaters constantly on and I could hear the filament bubbling on my hotend. Yikes.

It's a unintended feature of the Duet 0.6 and 0.8.5 hardware design that if +3.3V is shorted to ground but +5V remains active, all the heaters turn on. The burned out processor is probably shorting +3.3V to ground. In the Duet WiFi design I added extra gating so that both +3.3V and +5V need to be present for the heaters to turn on.

Edited 1 time(s). Last edit at 09/24/2016 07:41AM by dc42.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Oh that is good news, now I know I probably won't kill my Duet wifi like that