Thanks for your reply.
I had 3615 installed with bootloader 1.03b.
i dont know which DSM i had i think 6.17 and accidently upgradet to 6.2
Now i tried it with your tip and used the extra.lzma. The device is booting and shows "Screen will stop updating shortly, please open find.synology.com to continue."
i cant find the NAS on Synology Assitant or find.synology.com