I'm such an idiot... A while ago, after a thorough inside-out cleaning of my Vic, I put plastic (kitchen) film over it as a dust cover. When I loaded Pulse I didn't think about it as I didn't really need the keyboard. I just plugged in the joystick and let film stay wrapped around the Vic... I didn't think about until now and now I'm scared that I indeed have overheated and perhaps damaged my dear first computer
I brought out my back-up Vic and after much fiddling with the tape azimuth got Pulse to load. Played very well for two trial rounds and then I thought it was time to get serious, time to break my seasonal best - but at 513 p my backup Vic hung too... This was actually a relief as I consider it a sign that my original Vic wasn't overheating.
But it is still weird. I don't remember my Vic hanging even once last summer when I played it every day for a week.
Well, will switch back to my main Vic again (now without plastic film!) and try once more for a high score before I go to bed