I take it this is a common problem with these old Pioneer LD players. Mine gets stuck when you try to switch to Side B. It's the exact problem this gentleman had with his Pioneer:
Like his, you have to yank the power cord to get it to come back to stop position.
This probably started maybe 4-5 years ago, after the player had been rarely used for years.
I took the lid off and put some white lithium grease on the plastic gears I could reach back there. No improvement. I found I could occasionally coax it to play side B by pushing slightly on the turning mechanism as it was almost flipped over - maybe 2 times out of 10 if I caught it just right, but I couldn't quite figure exactly what I was doing or what specific part may have been at fault. I hoped perhaps if I did that a few times it would sort of come back to life but no such luck.
The gentleman in the YouTube thread said he found the problem was the "small plastic carrier in the changing mechanisam that was busted (thon one that holdt the laser ribbon." but I'm not quite clear what that means. Any thoughts? Is this worth fixing at this point? I did acquire another working (Sony) LD player in its place but I'd prefer to keep this old Pioneer if I can fix it cheaply enough. Not worth spending $100 USD on - maybe $20 USD...