[3.4.0beta6] After update: Heater 1 fault shows 409.9 °C

[juliann]

@dc42

Sorry I forgot to mention, there is no possible contact in the back of the toolboard everything is plastic and it is correctly protected to avoid issues.

[dc42]

@juliann please email warranty@duet3d.com. You will receive a response with a link to a form to fill in.

[juliann]

@dc42

It's done.

Thank you very much.
Julián.

[juliann]

Hi @dc42

Sorry, the problem persists.
I received the Toolboard replacement and worked perfect during the first 5 prints.
During the last one, a heater 0 fault suddenly appeared interrupting the printing (while reading 241°).
After pressing emergency stop, the temperature reading went to 980° (just the reading, not actual temp).
The ambient reading now is 280° no matter if I reset of turn off/on the printer.

So I did the same as before, I changed the temp port in the toolboard and now in the temp1 it seems to work again. Any ideas?

Thanks again
Julián.

[T3P3Tony]

@juliann Please can you send a picture of how the board is mounted and wired. A good clear high resolution picture of the board itself as well.

In addition please check carefully for any shorts between your thermistor and the hotend heater wires.

[juliann]

Thank you @t3p3tony

All the parts in contact with the tool board are plastic, just two screws are used to mount it. At this moment I am using the temp1 of the tool board without issues (same way as I did before with the previous one).
If I switch back to temp0 the problem persists.

As I just replaced the tool board the current wiring is not organised, I just put a coupe of ties to keep cables in a safe position.

Please let me know if you need more photos/ information.

[dc42]

@juliann I have received and examined your first tool board that showed this problem. The fault is caused by a burned-out reference resistor. The only reason I can see that resistor would burn out is if the TEMP0 input is shorted to a 24V supply for more than a few seconds.

As this has happened to two tool boards, what I think is happening is that you have an intermittent short circuit between the thermistor and the hot end heater. There are various ways this might occur, including these:

• A hot end heater and thermistor wires touching where they are not insulated
• Hot end heater cartridge shorting internally between the element and the case when it gets hot, and the thermistor wire touching the hot end metalwork

Unlike most 3D printer control boards, Duets are normally resilient to this type of short circuit - and the tool board microcontroller was indeed protected in this instance. However, the small size of the resistors used on the tool board means that the sense resistor cannot tolerate a short circuit to 24V for more than a few seconds before it fuses.

I have replaced the resistor and the board is now giving the correct temperature readings, I will contact you to arrange a swap of this a tool board with the one you currently have. Meanwhile, please locate and fix the intermittent short circuit.

[juliann]

Hi @dc42

I just got you email, thank you very much for the detailed explanation.
I will recheck very carefully all the tool board wiring and send it back to you.

Thanks again
Julián.

[dc42]

@juliann you should have received your repaired tool board by now.

I have received and examined your second tool board. It has the same problem, i.e. the series resistor has gone open circuit.

I originally thought that only a short from TEMP0 to +24V cold cause this type of failure, however on researching this I have read that small resistors can be damaged by ESD. So if you are sure that there have been no shorts, then it is likely that ESD caused the failures.

The best way to guard against ESD would be to connect the hot end metalwork to ground on the tool board, either directly or through a resistor in the range 10K to 1M. You can pick up a ground connection on the IO_ connectors. The advantage of using a resistor is that if you get a short between the hot end metalwork and the heater cartridge, the tool board will be protected from damage.

[juliann]

Hi David @dc42

I am currently rewiring the the ground using a 10K resistor.
Before you send me this message I bought another Toolboard v1.1 and installed it with a new thermistor and heater, but after a few prints I got the same issue (with temp0) so I think you are right, as there is no chance to have been shorts in the installation an ESD should be the explanation.

BTW I already received this morning the repaired tool board.

After finishing this installation, can I send you this second tool board to repair it as well?

Thank you!
Julián.

[dc42]

@juliann said in [3.4.0beta6] After update: Heater 1 fault shows 409.9 °C:

After finishing this installation, can I send you this second tool board to repair it as well?

Yes, please do.