Hot end thermistor issue on autotune - now showing -20 deg

[senake]

Hello All,


I am very close to getting my Rostock finished, but something strange happened when I ran the hot end PID autotune with the M303 S200 command. As shown in the image below, there was quite a bit of lag between the hot end temperature and the thermistor, then when the hot end got to 200 degrees, the thermistor temperature stopped climbing and dropped off. It kept falling - gradually, not immediately - to below -20 degrees at which point I disconnected the Repetier and switched off the Rambo.

Is it likely that I BBQ'd the thermistor or could this be something else like damage to the Rambo? Does Repetier estimate the hot end temperature (pink line on the graph) by measuring the change in resistance of the heating resistor or in some other way.

Any help would be very much appreciated.

[img]http://www.flickr.com/photos/103588472@ ... /lightbox/[/img]

Image link: http://www.flickr.com/photos/103588472@ ... /lightbox/


Thanks




Senake
London

[jesse]

-20c means the thermistor is disconnected. 366c means that the thermistor is shorted.