Hello,

I would like to present another remedy to an accidently corrputed 
open-firmware nv-ram
- WITHOUT having to replace the p-ram battery!

I own a power mac with OF version 2.0f1 (it is the beige G3 desktop).

While trying to boot my freshly installed NetBSD 2.0 (on a separate 
disk, yet unsuccessful),
I poked around in the OF variables section a bit. Let me mention that I 
normally know what I am doing ;-).

I encountered the situation that OF even did not show me the prompt 
when I was holding down the
appropriate keys at boot chime time.
Luckily, the mac still let me zap the p-ram contents (using 
<option>-<command>-P-R).
The aim was to boot into MacOS-X again.

Here is the way that helped me out of that pinch.
It might be of some use for others as well.

=====================================================
- Get your MacOS-X installation CD no. 1 and insert it into your 
default CD-ROM drive.
   You may need to re-boot once more (<option>-<command>-<power>) to get 
the drive door opened.
- Reboot the mac and reset the parameter ram using 
<option>-<command>-P-R.
   (You know you have the press the keys down till you hear the second 
chime.).
   Reboot and press down these keys to have the ram reset a second time.

Now the system should be able to boot MacOS-9 again, but the nv-ram is 
problably still in such a mess
that booting into MacOS-X is not possible.
But, the system should be able to boot from the MacOS-X installation 
CD, and this does the trick.

- On the next boot chime press down and hold the C key to make the mac 
boot from CD.
   While it boots, is restores the necessary nv-ram settings, and 
immediately re-boots a second time,
   as you might remember.
- Now, you can either let the mac boot into MacOS-X from CD and then 
use the startup-volume preference
   pane to set your MacOS-X drive, or boot into open-firmware and type 
in the correct boot-command and
   boot-device if you remember them.

When you are back in OS-X, you may have to re-apply certain settings 
such as screen resolution.
======================================================

This helped me without haing to open my mac and unplug the system 
battery.
Please let me know if this method helps on other systems as well.
I hope you understand that I did not try the solution a second time ...

Best regards
Bernhard