no power to heat bed terminals



  • New Duet Maestro. After two days of running lost power to on board heat bed terminals. The bed is powered through off board mosfet so only signal leads attached to board bed terminals. All thermistor headers give 1.8 ohm reading and work ok. I notice heat bed led does not come on. I’m new to the Duet system and not too good at electrics but I understand this might be the on board mosfet or line tracer failure. I would be grateful for any advice or next step to take.


  • administrators

    Hi @ortondale,

    That sounds a most unlikely failure. Have you upgraded the firmware or made any changes to the config.g file recently? Is the extruder heater still working?



  • Yes, tool 1 heater working ok. Removed hot bed from g-code and slicer software disconnected heat bed and thermistor from printer and ran a test print on cold bed, all worked fine. Initially I set the duet up and ran through test modes and couple of small print files. Then ran six hour test print using latest Cura and board at default settings for pla, all ok ran perfect. Next day reboot, load file to print same settings and get error heater 0, sensor open circuit or unknown temperature sensor channel. Had a good look at board and can see no obvious signs of component failure



  • @dc42 Yes, tool 1 heater working ok. Removed hot bed from g-code and slicer software disconnected heat bed and thermistor from printer and ran a test print on cold bed, all worked fine. Initially I set the duet up and ran through test modes and couple of small print files. Then ran six hour test print using latest Cura and board at default settings for pla, all ok ran perfect. Next day reboot, load file to print same settings and get error heater 0, sensor open circuit or unknown temperature sensor channel. Had a good look at board and can see no obvious signs of component failure



  • Think you should make sure if the issue is the sensor or the fet, or both?

    Does the bed termistor work if you connect it to another input?

    Does the bed turn on if you run it as a regular pin and not a heater? Copy this into a macro and run it to see?

    M140 H-1
    M307 H0 A-1 C-1 D-1
    M42 P0 S1
    G4 S10
    M42 P0 S0
    


  • @bearer Thermistor to another connector gave a negative result. Ran your macro and the bed heated ok so re-checked bed thermistor. Rightly or wrongly I used the bed thermistor tracers and soldered the thermistor at the centre of the bed. Consequently I’ve ended up with a dry joint. Wired a new thermistor directly to board connector and running ok at the moment. Thanks a lot for your help


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