I made the error of setting the console path to graphics in the BOOT_ADMIN console of an old HP apollo 715/50 workstation with no monitor connected (or at least none that is able to detect the system's VGA signal).
On more recent HP 9000 hardware, it seems to be possible to reset the console path to serial by pressing the TOC button after powering on with no keyboard and monitor connected, but as the NetBSD/hppa FAQ (cache) sais, this has no effect on a 715.
As it turns out, there is another way though, and I haven't seen it documented anywhere: The 715/50 has a monitor selection switch for its onboard graphics adapter. It has one setting (both switches on SW1 down) that is labeled as 15" Color (Model 715/33 only) in the service manual.
With this setting, the system comes up with serial A as default with 9600/8/n/1, and it's possible to interrupt the boot process with <ESC>, select <a> to get into boot administration mode, and then change the console path back to serial from the BOOT_ADMIN> prompt:
PATH console rs232_a.9600.8.none
RESET
On more recent HP 9000 hardware, it seems to be possible to reset the console path to serial by pressing the TOC button after powering on with no keyboard and monitor connected, but as the NetBSD/hppa FAQ (cache) sais, this has no effect on a 715.
As it turns out, there is another way though, and I haven't seen it documented anywhere: The 715/50 has a monitor selection switch for its onboard graphics adapter. It has one setting (both switches on SW1 down) that is labeled as 15" Color (Model 715/33 only) in the service manual.
With this setting, the system comes up with serial A as default with 9600/8/n/1, and it's possible to interrupt the boot process with <ESC>, select <a> to get into boot administration mode, and then change the console path back to serial from the BOOT_ADMIN> prompt:
PATH console rs232_a.9600.8.none
RESET