Duet board seems to have burnt out - is there a procedure for checking?

Hi,

So, I started a new print, and while the head was warming up, the web interface disconnected, and when I was trying to hit the connect button on the web page, all of a sudden there was a puff of smoke from the Duet board.

I did not see where it came from, but I immediately switched the power off. While it did whatever it did, and before I saw there was a problem and shut it off, the extruder went high enough that it melted my PEEK parts.

I removed all the wiring except the main power connection, and turned the power back on. At first it looks like the board is working, and the end stops turn on and off when I click the switches. However, after about 10 seconds, a bunch of the LEDs start to flash red, so I shut off the power again. It appears that the processor chip is getting really hot.

Does this mean the board is fried??? Is there a trouble shooting procedure?

Edited 1 time(s). Last edit at 09/07/2015 05:15PM by patrickrio.

If the processor chip is getting hot, that is bad news. I have a couple of suggestions:

1. With 12V power applied, measure the voltage on the 5V rail. You can measure this betwen the two end pins on the expansion connector (the leftmost pins if you are viewing the top of the board with the Ethernet connector at the top right).

2. Look at component L7, which is by the corner of the processor nearest the SD card socket. Does it appear to be intact, or might that be where the smoke came from?

---

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].

I dont have a 12v supply here... will have to go get one from a friend.

I think L7 might be where the smoke came from. very very burnt.

I have already ordered a replacement board.

So, what happened???? did I get some short that I need to look for and fix before i put the new board in??????

Edited 1 time(s). Last edit at 09/07/2015 09:54PM by patrickrio.

I have seen a few reports of L7 getting burned out. This will happen if there is a short between one of the 12V heater connections and the ground side of one of the thermistor connections, for example if the hot end is mis-wired. Also, the Duet 0.6 places the hot end thermistor ground pin right next to one of the hot end heater pins, which also means that if you accidentally plug the hot end heater connector into the board shifted by one pin position, you will end up creating such a short. I added a note about this at [reprap.org]. The Duet 0.8.5 board moves the hot end thermistor connectors away from the hot end heater connectors.

When I said a 12V supply, I meant whatever voltage supply you are using to power the board.

Edited 1 time(s). Last edit at 09/08/2015 07:24AM 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].

the teflon was melted off my thermistor where the screw holds it in place. It looks like I got runaway heat that then caused the short out to the aluminum block. Not sure how my heater wire contacted the aluminum.

2 questions:

1. how do I get runaway heat like that?

2. is there a way to get the heater block to conduct electricity to the aluminum on accident without the wire touching? The wires seemed far from the block....

Quote
patrickrio
the teflon was melted off my thermistor where the screw holds it in place. It looks like I got runaway heat that then caused the short out to the aluminum block. Not sure how my heater wire contacted the aluminum.

2 questions:

1. how do I get runaway heat like that?

2. is there a way to get the heater block to conduct electricity to the aluminum on accident without the wire touching? The wires seemed far from the block....

Perhaps you had a short between the heater negative wire and the thermistor ground connection? That would explain both the thermal runaway and the burned out L7.

The other situation I know of that causes thermal runaway is a short from +3.3V to ground, or a failure of the 3.3V supply for some other reason. If the ATSAM mcu is getting very hot, then it may in effect be shorting +3.3V to ground. So the thermal runaway may be a result of the mcu failing, not a cause of it.

---

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].