On Sep 6, 6:57*am, Richard Rasker wrote:

I've been asked to fix a special piece of lab equipment, a Hewlett-Packard
214B Pulse Generator, dating back from 1980 or thereabouts.

The problem is relatively straightforward: a chain of components in
the -155V supply has blown:
* PCB fuse F602, value unknown
* Q601 and Q602 (MJ15003)

Since the fuse (F602) has literally exploded, there's no way to determine
its original current rating.

Look for labels, or silk-screened indications of the fuse type and
rating...
you never know.
It might be possible to analyze the exploded bits, of course.
Collect
them all!

If it helps, MJ15003 is rated for 20A, max. The
safe-operating-area limit is a polygon on log(I)/log(V) paper with
nodes at
[ 20A, 10V], [5A, 50V], [0.5A, 140V].