My Countax C800H 42" cutting deck is not rising and lowering as it should. It's fine when you're lowering it but trying to raise it is an issue. It'll get up to position no 5 then won't go any further. Any ideas on what the issue could be?

Also the tension belt keeps popping off. I've tried adjusting the belt tensioning rod but this hasn't made a difference. Before I fork out for a new belt does anyone have any other ideas re fixing this issue?

All advice gratefully received!
Thx