How to recover a root partition with damaged boot blocks

["Thomas Mueller" <mueller6725%twc.com@localhost>]

How do you recover a partition with boot blocks rendered nonbootable?

There was a split-second power outage during a high-wind event that damaged the root partition, rendered it nonbootable.

I built the computer in June 2011, one of the early UEFI-capable motherboards.

I was able to recover the file system with fsck_ffs (ffsv2, I believe) but not make it bootable again. 

User data on /home partition was recovered all intact.  I also have a NetBSD installation on the other computer (June 2013)

NetBSD version is 9.99.82 amd64, which I also have on the other (June 2013) computer.  I also have NetBSD 9.99.82 on each computer for both amd64 and i386.

I tried to rebuild the OS to NetBSD-current amd64 from i386 installation.  That was working up to the install stages, when build was stopped due to lack of entropy at 9 hours 10 minutes (not a selling point for NetBSD).

The affected partition can be mounted and read, but when I try to boot, the computer immediately reboots, no error messages.  

I normally boot with a version of the Super Grub2 disk image.  When, at the grub2 command prompt, I type "knetbsd /netbsd-99982" and then "boot", computer immediately reboots with no error message.

I also tried to boot by UEFI but could not even get that to set up right.  I read "man boot" many times.

I checked /boot and /usr/mdec, even ran installboot from NetBSD-i386 installation, but nothing worked.  Is there any way to recover?

Tom