Temperature for Bed and Extruder way too low

Hi guys,

I've finally managed to reach the stage where I can turn on my little Huxley, but I'm getting very strange temperature readings for my bed and extruder temperatures, as you can see in the attached screenshot.

I get the below after pressing "Check temp" when I connect to the printer via Pronterface (Screenshot in file Temperror.png)

T: -273.1/ -273.1 B:-14.3/-273.1@:0

And this is the reading I get when I unscrew the wires for btemp and etemp from my Melzi V2.0 board. (Screenshot in file Temperror2.png)

T:-40.9/ -273.1. B:-39.7 to -41.4 (it fluctuates)/ -273.1 @:0

Does anyone have any idea what is the issue I'm facing?

Hi KennethY89

It sounds like you've got a short circuit on your hot end heater, and no connection on your heated bed. Check your wiring. There's a troubleshooting guide to bed temperature problems here: [reprappro.com]
Looking at your configuration (M503), it looks like the thermistors are set up correctly (the M304 responses)

Ian
RepRapPro tech support

Hi Ian,

Thanks for the tips and pointing me to the troubleshooting section

It seems that I indeed have a short circuit in my thermistors, because I get massive resistance in my wires for both the hot end and bed, and not the typical 100k ohms. If that is the case, is my Melzi board considered condemned, or do I just need to redo my wiring on the hot end and the heated bed?

No, I think it's just a wiring issue. You can test the Melzi's temperature response by putting a known-value resistor (values between 1k and 100k ohm should give sensible readings) in the thermistor screw terminals. This is explained better, and a list of temperatures you should see, in the troubleshooting guide I linked in my first reply.

Ian
RepRapPro tech support

Hi Ian,

Thanks for the help! I managed to get my bed temperature reporting properly after redoing the wiring. However my extruder temperature still gives me the -273.1 degree output on Pronterface. Here are my findings from the troubleshooting guide steps

1) Check the temperature in Pronterface. Is the reported temperature the same?

The reported temperature is hovering at -39 to -40 degrees

2) Bridge the screw terminal connections with a piece of wire. Is there any change in the reported temperature?

The reported temperature is hovering at -273 degrees

3) Testing with some resistors yielded the below results

150kohm : 17.7 degrees
100kohm: 25.5 degrees

I didn't have any other resistors.

Considering the results, what is the issue am I facing and how may I go about resolving it?

Hi KennethY89

From those results, I'd say the Melzi is okay, and it's still a wiring issue. If the resistors connected to the Melzi are reporting the correct temperature for their resistance values (and I would say they are), either you've got the wrong value thermistor, or you've still got a break in you wiring. Remove the thermistor wires from the Melzi, and measure the resistance across the wires (ie the resistance of the loom, up to the thermistor, and back again on the other side of the loom). If it's infinity resistance, you have a break in the wiring. If there's no resistance, you have a short in the wiring. If it's somewhere above 200k ohms, you'll may have the wrong, or damaged, thermistor.

Ian
RepRapPro tech support

Hi Ian,

I just managed to get everything working, and it is like you said. I mixed up the wiring for the heater cartridge and the thermistor, which created the problem. Now everything is fine Thanks so much for the assistance!