Help with Sun 2! (cpu + prom = no video?)

[Walter Mischel]

I hope there still are people who run, or remember, sun-2. We have one of
these venerable ones which has recently developed some intermittent
hickups (parity error -- core dump -- reboot). Luckily the machine was on
sun "mail in" service contract, so we promptly got a new CPU board from
sun. However, the new one doesn't work! The LED self-test indicator on the
board shows that the board is ok (4th LED slowly flashing). But the
console gets no output (normally, it puts a sun logo, identifies the PROM
revision #, serial #, ethernet address etc.  before it goes on to load
UNIX -- but none of that appears).

Then I put in the PROM's from the old CPU board (which had intermittent
problems) into the new CPU board, and suddenly system began to work. 

The sun engineer I talked to on the phone found a sentence in his service
manual which said that when there is a type mismatch between the PROM's
and the cpu board, video output will be disrupted. But it didn't explain
further. 

Has anyone experienced anything like this?  How does one find out if a
particular PROM matches of a particular cpu board? What is the relevant
characteristics of the PROM and the cpu board (revision #? multibus vs.
multibus prime? 128K version of PROM vs 256K verson?)?

I want to find this out because the current combination (new cpu board,
old PROM) still has intermittent problems, only with higher frequency
(once or twice a day!). So I want to get a replacement cpu board from sun.
But since even they don't seem to know how to tell exactly what PROM works
with what CPU board, I'm turning to the collective wisdom of the net.
Otherwise, there is a shot-in-the-dark quality in continuing to swap just
in hope to come upon the right combination. (Also is there such a things
as cpu board - video board matching problem?)

Any clues, hints, suggestions, and rumors are welcome.

Thanks!

Yuichi Shoda
yuichi at luna.psych.columbia.edu
406 Schermerhorn Hall, Columbia Univ. NYC, NY 10027
212-854-8450