On the mainboard is a 2×3 6-pin header with a jumper where one of the center pin is missing.

• unplug power
• open case
• set RCV jumper
  • when the missing pin is at the top, bridge the two left pins with the jumper
• plug in power
• start system
• press F2 to get into the BIOS
• save BIOS settings
• shut down system
• unplug power
• put the RCP jumper back to its normal position
  • when the missing pin is at the top, bridge the center and the right pins at the bottom with the jumper
• close case

• obtain BIOS firmware update
  • you can download it from https://support.ts.fujitsu.com/IndexDownload.asp
  • I used a file called
    • D3543A1xAdminpackageCompressedFlashFiles_V50013R1140_1302609.ZIP
    • sha256sum 1c6b6acd8520d54f5e3ff8fa8030b7340c242ce051e065b16a13581e5b131125
• prepare a USB stick with a BIOS firmware update
  • MBR partition
  • FAT32 file system
  • extract downloaded ZIP archive and just copy all the files to the USB stick
• unplug all external devices
• unplug power
• open case
• set RCV jumper
  • when the missing pin is at the top, bridge the two right pins with the jumper
• plug in the USB stick in one of the two USB 3 ports at the front
  • it does not work with any of the USB 2 ports at the back
• plug in power
• wait a moment
• success is notified with a single beep
• progress is notified with many random very short bip
• afterwards there is a moment of silence
• followed by a pattern of beep - beep - beeeeeeeeeeep - beeeeeeeeeeep
  • the two long beeeeeeeeeeep at the end are very long both
  • they are the sign that BIOS recovery was successful
  • from pluggin in power to this point it did no even take 30s in my case, the manual stated 3-5min
• unplug power immediately
  • if you don't unplug power directly after the two very long beeeeeeeeeeep it restarts the BIOS recovery automatically (and you might not want this)
• remove the USB stick
• put the RCP jumper back to its normal position
  • when the missing pin is at the top, bridge the center and the right pins at the bottom with the jumper
• close case
• plug in power
• the system should boot again
  • first boot takes quite a long time
  • but it displays the Fujitsu logo quite early when it is plugged to a monitor, so that is a good sign