[SunHELP] sparc 10 crash - help needed

[Arthur Wouk]

here is my first post. the current state is described below.
:
:my sparc 10 crashed today. the main symptom is a lack of symptoms.
:
:i removed the keyboard and monitor, attached them to another sparcsattion
:and it boots just fine.
:
:if i tip to the dead sparc 10, i connect but get no response when i
:power reset.
:
:when i reattach the monitor and keyboard, and power on with stop-d
:keys held down, the leds on the keyboard go on and off two times, then
:everything halts with only the caps lock key illuminated. thus the
:POST does not run. the monitor's signal light keeps flashing - it is a
:GM 20D10. there is no signal to the monitor apparently.
:
:is this a power supply failure, a boot prom failure or an nvram
:failure? any clues as to how to test?
:

i reported the crash a few days ago. i now have the maintenance
manual, and it confirms that the power supply is fine: both test
criteria are satisfied: the led on front of the case  lights up, and
the keyboard emits its desired aqueak.

however, there is no output either to the monitor or to serial port A
when i power on while holding down stop-d. the heyboard LEDs go on and
off twice, and then i am left with the cap locks led on permanently,
and no other signs of life. 

this leads me to think that the boot PROM is fried. would a fried boot
prom cause a crash in mid-operation? a fried boot PROM would fail in a
manner similar to  what i have described.

i do not believe this is a problem with the cpu - it is not involved
in the POST, only the boot PROM is. it cannot be a problem with the
drive, which starts up normally (which i can feel with my hand on
power reset) and is not involved in the POST.  it can't be the frame
buffer since i get the same result coming in through serial port A.

so i am left with the motherboard. how do you test a motherboard?
i am guessing that replacing the boot PROM is the only feasible test.
if that doesn't fix it, i gues the MN is shot. 

does anyone have any other analysis or insight?