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Heat bed suddenly stopped working  

New Member
Heat bed suddenly stopped working

In the middle of a print, the heat bed suddenly stopped working. Everything works fine with the exception of the heat bed



  • LED on heat bed connector - No
  • LED6 on mini-Rambo - No
  • Power input (X10 AB, and X10 CD) – 12V, Molex connectors ok
  • F3 Fuse (15A) – Ok
  • Terminals on heat bed - Ok
  • Heat bed cable – Ok
  • Heat bed resistance – 0.9 Ohm
  • Heat bed connector (X3 AB) – OK
  • 12V3 – 10.55V when idle, 11.85V when heat bed and hot end is set active


I have gone through the wire diagram and verified all component, where everything seems to be ok. The mostfet is difficult to test without de-soldering it, but there are no short circuits which would be natural of a mosfet failure.

What I did found was that the PWM output (port 1) on the Atmel I only gave 0,85V when heat bed was supposed to be on. When the target setting is set well above the thermistor readback, I would expect something in the range of 4.5-5V?! The PWM output (port 2) for the hot end shows 4.99V when activated.

I have done a factory reset and upgraded to the latest firmware – heat bed still not working

This is actually the second time this happens – last time I replaced the mini-rambo with a second hand piece I got my hands on.

Any thought? Please help.

Posted : 04/06/2022 9:11 am
RE: Heat bed suddenly stopped working

Any success?  Have you contacted support via chat?

Chuck H
3D Printer Review Blog

Posted : 13/06/2022 9:38 am
Active Member
RE: Heat bed suddenly stopped working

That was what happened to me a few times before my PSU capacitor died.  I had to get a new PSU.  I inserted the one that I purchased because Prusa does not carry the PSU for the MK2 anymore.  Good luck!

Posted : 20/09/2022 9:57 am