After burning a couple of test CD's under MacOS at home I rebooted my 
8500 into Open Firmware and started the games, er, tests.  Failing 
the first test I took a look at nvramrc and found if unusually full 
of strange gook.  So I fired up nvedit deleted everything, quit, 
nvstore, nvedit, dead command line.  Oops.

Seems a completely, utterly empty nvramrc is not a valid state.  Also 
I hadn't set use-nvramrc? false.  When I did the three-finger salute 
to reboot I got the chime and a black screen.  Repeated attempts to 
restart with and without cmd-opt-P-R gave the same results.

All's well that ends well, mostly.  I took out the backup battery, 
unplugged the machine, waited a day, put the original 604 back in and 
everything came back up (slowly).  Only residual problem I see is 
that starting Netscape crashes the machine, but that could be due to 
my swapping a disk while I had the case open.

*whew*

Signature held pending an ISO 9000 compliant
signature design and approval process.
h.b.hotz@jpl.nasa.gov, or hbhotz@oxy.edu