See /pub/NetBSD/pmax/mdec-march-7/README, boot-dd, rzboot and bootrz.

These bootblocks print out somewhat more information when
they encounter an error.  I haven't gone into the UFS code
and put diagnostic messages there; but an error code from open()
is likely to be helpful.

These worked for me on a 5k/200 and 5k/240, and all I changed between
this and the version that worked on a 3100 and a 5k/25 was adding the
printf()s in stand/boot.c.

I hope this is of some help to those who were having problems
with the Valentine's Day  bootblocks

--Jonathan