Well I do experiment with my 3550 drive and try to convert it to 4551 with some tool necbfl, but during the process of bootcode flashing my monitor turned blue (BSOD).My drive led was blinking and the drive was totally dead.I tried to reflash with same tool but nothing still dead.I also tried nec converter, binflash-still nothing I got message can’t go to safe mode.I was desperate, I mean drive is not so expensive but still.
After trying of everything I can possible remember I decided to give a shot to the original 1.05 firmware from nec site http://www.de.nec.de/softwareoverview2.php/id/1333 and on my suprise it WORK! My drive is no longer dead and it work again perfectly fine.
So bottom line is never give up even with bad bootcode flash!
Hope this help somebody.
PS: The only thing that not turned normal is 2 bytes from last 3 bytes in firmware.Before it was 355 now is 451.Besides that everything work fine.