Blown Fuse (MK3/MK3S/MK3S+)

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The Original Prusa i3 MK3 series printers are equipped with fuses to protect their 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.

Einsy RAMBo board

The MK3 series has a 24V Einsy RAMBo board. Just like its predecessor, this logic board has three removable automotive fuses.

The fuses we use are known as ATO blade fuses for automotive applications 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 same one.

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 Electronics assembly - Finalizing the Einsy-case of the assembly manual for more details.
3. Now you have access to the Einsy RAMBo. Pull the fuses out and inspect them. The photo below shows what the intact fuses look like. Inspect them from this angle and see if the little wire inside is not broken. In case you cannot tell if the fuse is broken, replace the fuse preventively.
   If you own a multimeter, you can check the components for a potential short. Multimeter usage will show you how.

PSU fuse

There are two versions of printer PSU. One is a silver PSU that uses a T5AL250V 20mm fuse (slow), and the other is the Delta PSU (black one) that uses an F8AH250V 20mm fuse (fast). You can check the pictures below for how to find the fuse in your PSU.

When you are replacing the fuse, make sure that the printer is turned off and disconnected from the power source.

• Find the PSU fuse, which is located just above the PSU's power plug.
• Remove the cover of the PSU fuse, the best tool for that is the screwdriver that comes bundled with our printer.
• Inspect if the wire inside of the fuse is intact. If it is damaged, then it must be replaced.

Delta PSU

Silver PSU

Replacing blown fuses

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 if changing it on the Einsy RAMBo.
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.