Rotel Power Amp gone awry

My Rotel RB-870bx power amplifier has been a workhouse, until recently.  I blew an internal rail fuse due to a speaker wire issue.  When I went to replace the fuse, I (falsely) assume the capacitor was de-energized as I had let the amp sit for over a week without powering it up.  I was wrong.  Thankfully, I was using a set of needle nose pliers with a non-conductive rubber coating on the handle because when I tried installing a new rail fuse I was greeted with a fireworks show, i.e. lots of sparks and crackles.  Glad to still be alive, I realized I should have been more careful.  In any event, I let the amp sit another week, made sure that caps were de-energized this time (tested with meter), and installed a new rail fuse.  
I turned it on, nothing connected, and the fuse did not blow.  I then connected it to my system, and turned everything on, and now I have a loud hum coming through the speakers.  I am thinking I may have toasted something inside the amp with my little fuse replacement goof up.  I'm not a tech, but I'm pretty sure it's not a ground loop as this amp uses a two-prong plug and I don't have any other devices in the system other than the surge protector which are 3-prong plugs.  I believe the sparky fuse event may have damaged something else, but I don't know.  Any theories?  Is this amp even worth trying to get fixed?  I only paid about $150 for this amp used, and I believe it is over 25 years old.  However, it is a well regarded design and sounded great.  Should I sell for parts?  Thoughts?  Thanks for your input!