[commodorejohn]

This thread mentions that you could be able to reset that firmware password by starting the machine without NVRAM, wait for the ok prompt, reinstall the NVRAM (carefully) and use set-defaults to finally clear the firmware password. I don't remember if I ever had to do that on one of my Sun machines, but starting w/o NVRAM is definitely possible.

Well, I tried this, but it just gets stuck starting the POST and never actually gets anywhere...

Sad to hear that. Does that help to bypass the POST:

Bypassing POST

POST may be disabled and bypassed. To bypass POST:

1. Prior to powering on the system, press and hold the Stop and D keys on the
keyboard

2. With holding down the keyboard Stop and D keys, press the Power-on to turn on
the system unit.

...from https://docs.oracle.com/cd/E19127-01/ult...561-11.pdf, page 48.

There it also reads:

Additional Keyboard Control Commands

Stop Key

If the diag-level is set to either max or min and the diag-level switch?
variable is set to true and POST is not to be executed when the system unit is powered on,
press and hold the Stop key and press the Power-on key.

Note: Press and hold the Stop key for approximately 5 seconds.

Stop and N Keys

To set the system NVRAM parameters to the original default settings, press and hold
the Stop and N keys before powering on the system. Continue to hold the Stop and
N keys until the system banner is displayed on the monitor.

I don't know if the latter is equivalent to the set-defaults command or if it just resets the diag[...] NV vars.

Other idea: You could try to install a compatible NVRAM (48T59) from another Sun machine, maybe the OBP issues a set-defaults automatically in this case. It shouldn't hurt to use the NVRAM of another machine. IIRC I once successfully reprogrammed the IDPROM of my Blade 100 in an Enterprise 250 because the OPB 4.x of the Blade 100 was missing the mkp/mkpl commands and I didn't knew how to reprogram the IDPROM using Forth's c! command at that time.

I did try bypassing the POST, but it didn't pay attention to me, or I didn't do it right (Pause/Break is equivalent to Stop on PS/2 keyboards, right?) I'm not keen on shelling out $50 for a replacement part, but I may just have to...