> So, how can I interrupt the diags (they take forever) and what\'s wrong ?

You can probably interrupt by sending a break.

> The diagnostics usually fail at the first try with 
> (sorry, no notes) eeprom blablaa wrote x expected y looping.

You don't give many details, but this looks like an empty eeprom
battery (It's actually a battery and a ram in a single chip). Look at
the sun eeprom nvram faq (your favorite search engine) how to do some
surgery on your eeprom to get at the battery leads. The trick is to
get 2 wires soldered on at the right places sp you can hang whatever
battery there.

Harald.