Temperatures would always report as acceptable (ie 20 degree cold) but I had to replace the original Melzi board in the winter.

Now the cold temp is about 46 degrees for both thermistors.

Using an E3D hotend now too, and neildarlow's firmware....

I just bumped up the temperatures for printing (since the bed was too cold for decent adhesion) so I'm still printing ok but I should get to the bottom of this issue sooner rather than later...

All I changed was the Melzi and this issue appeared....

The Melzi probably doesn't have the correct pull up resistors on the thermistor inputs. They should be 4K7 1% but some Melzis have 10K fitted.

Edited 1 time(s). Last edit at 06/23/2016 10:34AM by nophead.

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[www.hydraraptor.blogspot.com]

You can wire in additional resistors to bring down the 10k resistors to 4.7k which is easier than replacing the smd resistors. 10k plus 82k in parallel are needed across each 10k resistor.
The top right connector pin on the board gives access to one side of the resistors and the lower screw connector of the thermistor connectors to the other.

No firmware setting then?

I tested the board, it is indeed 10k....

Ralph, [www.sengpielaudio.com] comes up with approx 8.8k not 82k.... but thanks for putting me on the right track

8.8k is not available as a standard resistor but you can make one close enough by combining 10k and 82k in parallel.