The Manual is very funny ...
Code:
10.1 Flash Memory Recovery Mode
- Prepare a bootable USB stick as described in section Flash BIOS Update with a USB stick.
- Switch off the system and disconnect the power plug.
- Open the chassis and switch on "Recovery" (BIOS-RCVR) using the jumper / DIP switch on the system board.
- Reconnect the power plug and boot the system with the inserted bootable
USB stick.
- Boot the system from the inserted bootable USB stick.
- Change the directory with cd DOS and start the Flash BIOS Update with the command DosFlash. Then follow the instructions on the screen.
- Observe the update process on the screen, until it is finished. The recovery
update may take several minutes.
- Switch-off the system and disconnect the power plug.
- Remove the USB stick.
- Return the "Recovery" (BIOS-RCVR) jumper / DIP switch which have been
changed to the initial position.
- Reconnect the power plug and switch on the system. The system will be booted with the new BIOS revision.
- Check the settings in the BIOS setup utility. If necessary, reconfigure the settings again
Like ... "Boot the system from the inserted bootable USB stick." if the BIOS is bricked
EDIT 1: I attempted now for a 2nd Time and I definitely can hear a lot of power on/power off cycles (you can hear the "clicks" of a Relay, I assume inside the PSU) like after a BIOS Upgrade (probably because it needs to "recalibrate" the Memory Speed JEDEC Timings etc).
But nothing really happens. Then it gets stuck again.
EDIT 2: iRMC Log Shows
Code:
POST - A recovery capsule couldn't be located during BIOS recovery flash
A ... "Recovery Capsule"

? Like what, is this NASA Software or what now ?
EDIT 3: I'll try with a known working extremely old FreeDOS USB Stick that at least previously worked. No clue why this one doesn't ....
EDIT 4: with the Old FreeDos USB Stick it also didn't work
EDIT 5: with the Old FreeDos Stick AND with the Files of the Fujitsu downloaded BIOS in the "ROOT" Folder of the USB Drive, it started flashing automatically and beeping. At least something seems to have happened
EDIT 6: I flashed the Recovery successfully (1.38.0 to try a different one than the failing 1.39.0). But nope, still Stuck on the Initial Screen. I took less than to setup the other 5 Systems and lost an entire Day trying to setup this one
EDIT 7: What gives ?
I tried to switch back to the Low Firmware Version that was working before and it's still stuck.
Furthermore I don't know ... it seems it won't detect any Memory or what ? I previously also tried with a single Stick of RAM, same Result.
Or is this simply because the Boot Process is not going forward for some Reason ?
The VERY first Time it kept freezing just after selecting "Debian (Default)" in GRUB Menu. Now it's not even going to the point that I can enter BIOS Setup.
It seems well and truly broken.
EDIT 8: Now apparently the Boot Watchdog kicks in as well ...
Code:
BIOS POST Watchdog - Action: Power Cycle (Post Code: 0x78)
EDIT 9: Damn ... it looks like you cannot downgrade the firmware even in recovery mode

Googling
fujitsu tx1320 m3 downgrade bios states
[I]Downgrading is disabled by default from the tool provided by fujitsu. You need to disable the BIOS build date time checking in order it to work.[/I]that on a Fujitsu Forum Thread, but unfortunately all of them have been taken down and Wayback Archive Machine doesn't contain those pages apparently
I can only read part (maybe the full ?) of the Command, but still that doesn't help, because Recovery Firmware is an automated Process, despite what the Manual Says (change Directory and Run Script)
EDIT 10: Now after powering off for a bit and another Recovery Flash using 1.30.0, it seems to be on that Version.
Still stuck at boot though but at least the CPU and 1 x DIMM (I temporarily removed the other 3x) are getting detected ...
Not that it matters, at the end of the Day, it's still NOT working at all ...