Recently, we faced an issue with our 1 year old Ormerod 2,. When I turned on the machine, the heat bed thermistor was reading 175 C at room temperature. When I opened the Duet, I found that the resistance across the head bed thermistor terminals was locked at 98 Ohms. The hot-end thermistor behaved normally.
When I opened the head bed thermistor, it measured 8K Ohms - normal. When I looked at heat bed thermistor terminals it still showed 98 Ohms. When I shorted the terminals, it was reading 0 Ohms and the Ormerod 2 reported 2900 C - so it seemed as if the ATMEL chip was ok, but something was wrong in the circuitry path. Tracing through the circuits, I saw that there was a capacitor C19 (10 uF) and a resistor R21 (1 K Ohms for the older Duet boards). I de-soldered the capacitor and checked the resistance across the SMD capacitor. It read 98 Ohms. So, it seems the capacitor might have blown out for some reason. Without replacing the capacitor, I connected the heat-bed thermistor, and the Ormerod reported 30 C and normal operation could commence.
So, my question is, can I continue to work my Duet without putting back the C19 capacitor on the Duet. I think I might have damaged one of the pads on which the C19 sits, so rather than junking the Duet, I would rather just use it. The casualty might be unstable or slightly inaccurate bed-thermistor values, due to noise. Any other problems/issues.
Alternately, I can add a 10 uF capacitor across the head bed thermistor terminals, but really, it makes the board untidy and I worry about future shorts, etc. due to messy handling. So, I would rather work without C19 capacitor, and really I am quite ok if the heat bed goes off by 2-3 C due to noise, etc. But I would rather get DC42's opinion and opinion from other experts.
Thanks
Sumant
Edited 1 time(s). Last edit at 08/27/2016 10:27AM by 7sumantb.
