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Thermistor failure Duet 0.8.5

Posted by Teilchen 
Thermistor failure Duet 0.8.5
November 18, 2017 08:24AM
David, please excuse me but I have to speak up to you in person.
Yesterday during a print my Kossel with Duet 0.8.5 printer went a bit crazy. As it happens I was not around, so I cannot say what exactly happened. But I found my printer with the head at a strange position, with one arm stretched beyond a straight line, with the head way outside the print area. The Web-interface was showing a thermistor error on the Bed, and E0.
I was able to home and then to restart the printer, and the web-interface was to able to reconnect, but both Heater0 and Bed Thermistors are still in error state, showing a -273C. The E1 thermistor is showing -3C, which is supposed to be 25-30C of the environment, but it has offsets configured, to match the heated chamber temperature.
I have read about the VSSA and 24v, and that a short circuit there will cause such a behavior. My L7 inductor does look a bit 'hot' around (it has a melted flux around) but it still has a continuity with a 2,2-2,5Ohm resistance. I was not able to get a clear foto of it. I have disconnected everything from the Duet, but left the PannelDue, and a spare, working Thermistor. Still no temperature readings.
The Atmel CPU is getting pretty hot, definitely hotter then it used to be, but the Web-Interface also shows -273C as CPU Temperature.

I measure 4.9V on a +5V line, and 3.1V on +3.3V line, all measured at the Expansion Connector, if this helps any.
The printer was working fine for two years with almost everyday printing.

Any idea what I should check? I have an access to a professional rework station, and people who would be able even to change the CPU if necessary.
Update:
here is a thermal image of my Duet controller, the CPU is roughly 80C hot, and the hotspot to the left of it seems to be a 5V Regulater, which is getting 60C roughly. The Duet was just sitting on the table, with nothing connected but a PanelDue.

Edited 1 time(s). Last edit at 11/19/2017 06:53AM by Teilchen.
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