Are you  able to boot the machine off of a CD, either NetBSD or Solaris?
If not, then I think your sparc might be toast.  I've got one of these
machines which was working fine, and then just stopped working.  I can't
even get it to the OK prompt.  Can you get yours to the OK prompt by typing
STOP-A or by pressing break on your terminal?  What about by pressing
STOP-N as it boots?  
	If you can't get into the PROM monitor, then
your trouble is most likely hardware related.

Hope this helps.
-Brian
On Nov 28,  3:30pm, Bsd Neophyte wrote:
} Subject: Re: data access exception error on boot w/ my sparc20
} 
} --- Bsd Neophyte <bsdneophyte@yahoo.com> wrote:
} > alright... i'm completely new to netbsd and not too knowlegable on unix
} > or
} > unix-like systems in general.  this is also my first post here... so
} > please, if i'm doing something wrong... be nice about it and let me know
} > instead of slamming me.
} > 
} > i've managed to install netbsd 1.6 on my sparc20 (128mb/9gb),
} > overwriting
} > my existing solaris 8 setup.
} > 
} > now i'm having problems getting the system up and running.  when the
} > system reboots, i get a "Data Access Exception" error along with some
} > numbers.
} > 
} > i've done a google search on this and maybe it's my poort search
} > abilities, but i haven't found anything that helps me.
} > 
} > therefore, i'm coming to you guys in the hope that you can dispense some
} > good advice or instructions on how to resolve this issue so that i can
} > start learning netbsd and hopefully make my own dns server.
} 
} 
} Can noone else help me with this problem?  I've already tried the boot
} disk/partition suggestion, but it won't work.
} 
} I really want to get this system up and running so that I can start learning.
} 
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>-- End of excerpt from Bsd Neophyte