Temp1 thermistor port fried, Driver 4 reported high temperature

Dakota

So the title is pretty explanatory as to the problem but I'm not sure as to how it happened. this is a Rat Rig V-Core 3 build with a duet 3 mini 5 that I am doing for a customer and I never ran into any of these issue while developing the build in my shop. The print was going well when they initially started it and then come in the morning the print was trashed with under extrusion and then at some point aborted the print as if there was never a print job that ran. The motors work and I've not been able to reproduce the fault scenario.

some other things to consider are:

The pt1000 thermistor is working correctly when I plug it into the temp2 port.
The print job that was ran has been ran multiple times beforehand.
The temperature in the shop was around 15c, so maybe it began to struggle to keep up with the requested temperature?

Any hints would be much appreciated as they need this machine running and I can get it working on the temp2 port but I can't figure out why it shorted now and not while I was developing the machine for them.

Dakota

Edit:
Apparently the issue also affected the Filament monitor. The light on the filament monitor is indicating error 4 which I can't seem to find any trouble shooting info on how to resolve that...

dc42

@dakota the magnetic filament monitor status codes are listed at https://duet3d.dozuki.com/Wiki/Duet3dFilamentMonitor_RotatingMagnetVersion#Section_Status_indication_LEDs.

Regarding the temperature reading error, we've had a small number of similar errors on tool boards recently and I am fairly sure that static discharge was the cause. We have long suspected that extruding filament causes static build up if there is no path from the hot end metalwork to ground, so the Duet WiFi and later include additional components to protect the microcontroller from excess voltage on the thermistor inputs. However, as electronic components have got smaller it has become apparent that the thermistor sense resistors may also be vulnerable to static discharge.

I therefore recommend that the hot end metalwork should always be connected to Duet ground, either directly or via a resistor in the range 10K to 1M. This will prevent static charge building up. To save on wiring, you can connect the hot end to the Vssa side of the thermistor connection via a resistor instead of to ground.

Dakota

@dc42 thanks for the response, I hadn't even considered that possibility, but given your expertise is much greater than mine and the logic sounds reasonable, I'll be sure to implement that into the Hotend assembly to protect it.

I do still have questions as to what the driver 4 reporting a high temperature issue. do you think that the event of the filament sensor getting excess static charge began affecting the the stepper motor driver? The wiring for the stepper motor (x axis in this case) wasn't in the same wire loom so I would assume the only point of contact could be on the board side.

As for the filament sensor, I did find the portion in the documentation and it say there is a 12c communication error. Me being a mechanical engineer, I'm very fresh in the data communication and coding aspects of engineering so I'm not privy to knowing how to solve an issue like that, nor did I find that information under the troubleshooting tab. Is it possible the static discharge could have affected the filament sensor as well?