Dead Z5 after full partition restore - Is bootloader bricked?

Hello, I sent my phone to warranty so I could get it repaired. So I backed up with twrp all my partitions (I'm BL Unlocked also). I got it back, flashed twrp, unlocked BL, and restored the full backup. Now I have a phone who won't boot up, even to the Sony logo, to fastboot, recovery or even flashmode. A 2-min reboot didn't helped. If I plug it in any power source, the red led blinks one time for half a second every 5-10 seconds.

Any way to reset the bootloader to default, as a wrong partitioning / restore damaged it ?

Thanks