Sa'Vasku power generators

I'm answering my own question here.

Sa'Vasku power generators must make threshold checks.  Why?

The rules explicitly state you can repair PGs.	How does this
force threshold checks?

I am playing Sa'Vasku, my first row of hull goes down and I
lose a PG.

I then fix it as per the rules.  Suddenly, because they never
take thresholds I never have to worry about that PG going
down again.

I just don't see that.	Also, the rules do not say they do not
take thresholds so they must.

About the needle gun thing, don't know.

Roger