Blown Fuse (MK3, MK3S)

Updated 4 months ago ​by Martin Lexa

The Original Prusa i3 MK3 series printers are equipped with a 24V Einsy RAMBo 1.1a board. Just like its predecessor, this logic board has three removable automotive fuses protecting the crucial components. If your printer or some of its components suddenly stopped working, it is recommended to check these fuses and replace them if necessary.

Each fuse protects a different part of the board.

  • F1 (5A fuse) - Motors + logic unit + fans
  • F2 (5A fuse) - Extruder Heater
  • F3 (15A fuse) - Bed heating

Checking the Einsy RAMBo fuses 

  1. Turn the printer off and disconnect the power cord.
  2. Open the electronics cover by removing the long M3x40 screw, holding the cover door closed. You may refer to STEP 21 of the assembly manual for more details. 
  3. Now you have access to the Einsy RAMBo. Pull the fuses out and inspect them. The photos below show what the intact fuses look like. Inspect them from this angle and see if the little wire inside is not broken.

If you own a multimeter, you can check the components for a potential short. This article will show you how.

Replacing blown fuses

If you find out that any of the fuses are blown, you can easily replace them. The fuses we use are known as ATO blade fuses for automotive application and can be found at any local car parts/hardware store or ordered online. It's a good practice to bring the blown fuse with you so that you can get the exact same one.

  1. Turn the printer off, disconnect the power and remove the blown fuse(s) from their sockets.
  2. Place the new fuse in the correct slot - Double check that you are replacing 5A for 5A or 15A for 15A. 
  3. Unplug any components connected to the previously blown fuse and try to turn on your printer. Check for any kind of unwanted behavior.
  4. Once again, turn off the printer and remove the power cord. Then reconnect all the disconnected components.

For further details about the Einsy RAMBo, see the picture below (your RAMBo board may be black/ brown instead of green, the color does not matter).


Find out more troubleshooting tips here: Community Forum | Assembly Manuals | Youtube channel |

How did we do?