I was turning the manual jack on my boat trailer today when, as the
wheel was just about at the
bottom of the jack, I heard a snap (or something like that) and now
the jack doesn't work. This jack
isn't bolted onto the trailer- it's welded on. So I'd like to try to
fix it.

Does anyone know how to diagnose and fix trailer jacks?

I popped the top cover off the jack and saw the gears and the handle
inserted into the jack
through the side. It all turns fine, and there is plenty of grease.
So it must be somewhere
between those top gears and... I'm not sure!... where the problem
lies.

If I can't fix it, I'll just buy a $30 trailer jack and bolt it on!

Thanks!
David