PC164 won't boot anymore

[Dave Huang <khym%azeotrope.org@localhost>]

This isn't NetBSD-related, but the machine in question does run NetBSD :) If 
there's a more appropriate list for this, please let me know...

My PC164 had been running fine, but I decided to upgrade from NetBSD 
4.99.something to 5.0_STABLE. I rebooted it to try the new kernel, but it's 
hanging early on--before it even gets to the bootloader, so it's not related 
to the upgrade. It prints this on the serial console:

ff.fe.fd.fc.fb.fa.f9.f8.f7.f6.f5.f3.f2.f1.f0.
ef.b0.b1.b2.b3.ee.ed.ec.f4.

then hangs... any idea what it means?