Okay, a bit closer here. I replaced this part with an identical part
(I had another Trinitron in the basement that had a bad degauss coil...
and all the attempts to repair that were useless). Result was still a
blown fuse, although this one didn't completely obliterate itself--the
fuse kindly popped and returned to normal. No nasty blue spark or
anything from the fuse. Maybe I replaced a Slo-Blo (or even medium
response) fuse with fast-blow, or maybe I still have a short somewhere
in the line. The original fuse was a SOC ST6 (125V 5A) fuse... though
I can't find any data on this. Size seems to be a 3AG.

I'll probably give it a rest for tonight and come back to it
tomorrow... make final checks with a meter before I go and replace the
fuse with something slower-acting. At least I've made some progress. :P