I had exactly this problem with the Sun 3/80 I am working on.
I could never get it to behave correctly without a working nvram.
If you go to the sun 3/3x archive at www.krupp.net, there is a lot of very
useful information there.  I wasn't interested in sinking  the $20 into a
new chip for my 3/80, so I used the battery replacement fix.  It worked
fine, and the intructions for re-programming the NVRAM worked as well.

-Steve Roylance