That's why we're here
The hiss makes sense. The flyback is arcing to chassis and bleeding off the HV causing a dark picture. Unplug the set, turn it on, let it sit for a couple hours to bleed out (you should technically discharge the anode to ground but we're not gonna have you do more than inspect), then undo the two push pins holding the flyback cover on, which is in the middle of the back of the chassis under the picture tube. I can just bet that the problem is there.
Then, power the set up, and watch from a distance with the lights off and see if you can see it arcing, and where it's arcing to. Might want to pick up a tube of RTV silicone, you'll probably need to seal up the flyback wherever it's arcing from.