Duet 3 fried

new_to_me901

@NeoDue it looks like I have a short where the thermocouple daughterboard connects. When I connect the multimeter (on ohm setting) to the +3.3V pin on the back of the duet 3 board and any other ground, the multimeter shows resistance. ~2.8-3.8. However when I do the same to the daughterboard itself there is no resistance.

I now see it would have been relevant to state the daughterboard has always given me trouble. Particularly when I had two thermocouples connected to it, it would power on with the Fault light showing on one of the two. I would simply disconnect and reconnect, power everything back on, and that would fix it. Sometimes I'd have to repeat many times. I tried multiple of these daughterboards and multiple duets, and still it happened. So I resigned myself to just check for the fault at each power up of the system. That seems like it was a mistake. Does this sound like it would have been the cause of the short?

I will continue to do more testing in the meantime! The continuity was the fastest/easiest to start with. Wires are next.

NeoDue

@new_to_me901 Hm, I fear I have no personal experience with the thermocouple daughterboard.

@oliof do you happen to know these addon boards or have someone in mind who could tell if that resistance is something that could be within expected ranges?

jay_s_uk

@new_to_me901 the temp daughterboard info is here if you need it https://github.com/Duet3D/TempDaughterboards

new_to_me901

@NeoDue Well as far as I know there shouldn't be any resistance at all between these two pins. It should read 0L, as it does for all other pins when connected to the ground. I also have a new duet3 board that hasn't been used yet, and it does not have resistance when touching the same pins: 3.3V and ground.

When I search the forum it looks like I'm not the only one who has had problems with the thermocouple daughterboards. Maybe I can get some good information from those threads.

dc42

@new_to_me901 when thermocouples give bad readings or the daughterboard error lights turn on, the most common reasons are:

Short circuit between one of the thermocouple wires and another wire (e.g. a heater wire)
Thermocouple element is not isolated from the hot end. The thermocouple elements supplied by E3D do have isolation between the element and the metal case. Many other types of thermocouple do not. If there is a short between the hot end metalwork and the heater (for example, because the heater insulation has broken down), or the hot end metalwork is connected to mains ground but the Duet ground is not, then this could feed a high voltage or transient into the daughter board, which could result in the chip failing and passing that voltage or transient t the +3.3V rail. That is likely to blow the 3.3V regulator and other components.

Can you disconnect the thermocouple from the daughterboard and use a multimeter to check whether there is any continuity between the thermocouple wires and the hot end metalwork?

new_to_me901

@dc42 Thank you for your replies. The thermocouples are insulated from the hot end.

I have checked continuity for these and have not found any continuity where it should not be. I've tried every combination possible, thermocouple to heater, thermocouple to insulation, thermocouple to heater wires, thermocouple to heater wire insulation, and then the same combinations through the heater power wiring.

I'm now working on powering the heater through an older heat controller so as to not fry another Duet if it is the culprit. Just want to see if it still works as intended. If it still works, I'm sort of at a loss. I've also seen that length should be taken in account for thermocouples. The thermocouple wiring is about 19.75 inches. Is this an acceptable length?

FYI we are using the v1.1 daughterboard with a k type thermocouple.

dc42

@new_to_me901 thermocouple wire length can be extended but you should use proper K-type twisted pair thermocouple wire to extend it. If you use plain copper wire then then you will move the cold junction to where the wires join, so the reference temperature measured on the daughter board by the chip won't be the same.

Please ensure that both the hot end metalwork and Duet ground are connected together, in case the problem was caused by ESD.

When and where did you buy the 6HC?

new_to_me901

@dc42 We did not actually extend the thermocouple wiring, so it seems like that isn't the culprit.

I will check for what you advise when I get back to the workspace later today and let you know.

We started using these boards more or less than 2 years ago, from filastruder a distributor in the US.

dc42

@new_to_me901 we may be able to suppy a refurbished board to you. Please email sales@duet3d.com with your details including a link to this thread.

NeoDue

@dc42 Out of curiosity: is it possible from your experience to fry a chip that much as it is visible from the last picture in post 1 with ESD currents alone? I have seen numerous failures from ESD from invisble but dead components to exploded ones - but never a chip housing softened and melted like that. I always thought ESD discharges are too fast to melt plastics like that, hence the question.

dc42

@NeoDue said in Duet 3 fried:

@dc42 Out of curiosity: is it possible from your experience to fry a chip that much as it is visible from the last picture in post 1 with ESD currents alone? I have seen numerous failures from ESD from invisble but dead components to exploded ones - but never a chip housing softened and melted like that. I always thought ESD discharges are too fast to melt plastics like that, hence the question.

I don't believe that the energy in a "normal" ESD would be enough to fry a chip in that way directly; but it may trigger a failure mode in the chip that causes it to draw a lot of power, or that subjects another component to excessive voltage. In particular, small 3.3V linear regulators usually have an absolute maximum input voltage rating of 6.5V and any higher causes a breakdown that causes them to draw a large current.

We know that ESD can directly fry small (0402 size) resistors.

NeoDue

@dc42 Sure - secondary effects... I completely ignored those. Thanks! My knowledge in that respect is getting somewhat rusty... still thinking in THT or (Mini)MELF dimensions here

droftarts

@new_to_me901 By the sounds of it, you also need to replace the thermocouple daughterboard, particularly as you say it has always given you trouble.

I would think you could test it with your spare 6HC without damaging it, but only test as described here: https://docs.duet3d.com/User_manual/Connecting_hardware/Temperature_connecting_thermocouples#troubleshooting specifically

If you have difficulty getting correct readings from the thermocouple board, try connecting a wire link between the two terminals of the terminal block instead of a thermocouple. This should produce a room temperature reading.

Ian

new_to_me901

@dc42 wow thank you so much, I will do that! I got caught up with some other things on Wednesday and am now out of town. I'm returning next week and will pick back up on testing. I've already got the new duet3, just want to make sure all components are safe before hooking it all back up.

@droftarts when we originally started using the daughterboard a year ago and ran into these problems, I actually tried other daughterboards on hand and got the same result. I also tried other duet boards with these daughterboards, and same results. So going forward, even if this heater still works, we're actually planning to change the sensor to a thermistor in order to bypass the daughterboard altogether. I may try these steps anyways though, just to see what it's current condition is... Thanks for the advice!

new_to_me901

@dc42 I have checked this and there is not short between the heater and the duet. I have also tested each individual component separately, and they all still work. Excepting the thermocouple daughterboard, we are just paying it safe and buying a new one. So still not sure exactly what happened here.
I am rebuilding with all of the tips in mind shown here. Plastic washers between the screw and board, and the board is mounted to plastic frame now. I have removed the peltier cooler from being controlled by the board altogether and am using a separate control board for this. I have docked it all in a computer case with adequate airflow and a fan to avoid dust. Hopefully all these combined will keep me good to go going forward!

Thank you to you and @NeoDue for all your help identifying points of improvement going forward. I appreciate it.

NeoDue

@new_to_me901 Then I cross my fingers your machine will run again soon