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Heated Bed always on

TooluserTooluser
in Extruder & Bed
The heated bed is always on even when the USB is disconnected from the board. I have tried firmware changes and hardware changes but nothing makes any difference. Is this a problem with the ATX power unit or am I missing something in firmware?  Any help appreciated. thanks from the ToolUser.

Comments

  • docpaycedocpayce
    Do you have a fan defined in the firmware? Seems to me that a fan might be set to blow all the time (e.g. to cool the PCB, the chamber...) but in fact the heated bed is connected to the fan pin. What board do you use?
  • TooluserTooluser
    thanks for that docpayce the board is a Arduino Mega 2560 with the 1.4 RAMPS, I will check this out when I get back to it later today.
  • TooluserTooluser
    Seems that I have power constantly on at digital pin 8 (heated bed connection) its showing 11.8 volts, have disconnected all fans and looked for anything relating to D8 in the firmware but don't see anything, any further ideas? ToolUser
  • TooluserTooluser
    I just uploaded Marlin firmware to see if anything changes, NO! still the same situation. So it must be a hardware issue? is there something in the boards that will cause this constant power on state? Any clues? Thanks ToolUser
  • RepetierRepetier
    A short between 5V and mosfet would cause constant power on or a defect on D8 pin.
  • TooluserTooluser
    OK Problem identified; please put this in the FAQ section for future reference. Pin 8 (heated bed) will always be on if you cross the polarity of the wires from the PSU! Also, don't let students do your wiring without checking it afterwards.  Thanks all ToolUser
  • RepetierRepetier
    Good to know that is is a possible cause. Never had heard about that.
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