How is the take-up spool driven? If by a belt, is that properly in place?
Is the take-up spool free to turn? The bearing may just be gummed up. See if the thing rotates freely. A (CAREFUL) application of WD40 may help (squirt it into a small pot and use a paintbrush to avoid indiscriminately spraying everything - especially any drive belt or pulley).
Just look and think. Follow how the take up spool is driven, look for things slipping and things sticking.
Look. Think. Understand., April 2016
