Flashing the firmware can sometimes fail, but most of the time it is nothing major. Before going deeper into issues related to flashing your printer, there are some initial steps and prerequisites that should be tested.
First of all, please try to use another USB port of your computer. Then hit the Rescan button in the Firmware flasher tool in PrusaSlicer.
Make sure the USB cable is inserted all the way on both sides, and maybe try another cable as well.
The Firmware Updater tool is not getting a response from the mini RAMBo or EINSY RAMBo board. Check that your printer is powered on. The next step is to check your fuses, you can visit these articles for more information: Blown Fuse (MK2S/MK2.5/MK2.5S) or Blown Fuse (MK3/MK3S/MK3S+).
"Wrong file has been selected for flashing". Make sure to unpack the .zip archive with the firmware and select the .hex file for your printer model.
When you see a status message “Flashing failed. Please see the avrdude log below.”, click the “Advanced: Output log” button to see the full flashing log. This log can provide more information about the reason for the failure.
In case you see at the end of the log a message “Could not open port: COM4” (or another COM port number), this can have multiple causes.
The above error can be accompanied by an error “stk500v2_getsync(): timeout communicating with programmer” (as in the picture above). When that’s the case, check if:
When the error “Could not open port: COM4” is accompanied by the error “arduino_open(): Failed to initialize MK3 external flash programming mode”, check your LCD screen for any further error messages.
Check if the printer is showing up in the Device Manager as a COM device.
Sometimes, the printer shows up in the Device Manager, but not among COM devices - If you can find the printer in the Device Manager, but not as a COM device, follow these steps:
If the Firmware flasher gives you an error saying it is not able to communicate on COM3 or another port, check your Port settings - some other device may be using that port. Eject that device, or change its com port to another number, and restart your computer.
After flashing the firmware, does your LCD show only squares? If the LCD and menu were working correctly before the firmware update, then firmware for different a printer model was flashed. Make sure you selected the correct one (MK2.5S/ MK3S/ Multimaterial).
The core of the printer's system (bootloader) is "read-only" which means that even if you upload an incorrect firmware or make any other mistake, there is always a way to make things right. The best practice when uploading or flashing simply does not work is to follow the steps for a Factory reset (MK2S/MK2.5S/MK3S) of all data.