I suggest you pick up a copy of "Niles Hokkanen's Guide To Mandolin Chords (and how to use them)". Mine came from Elderly Music in Lansing Michigan. The price on the cover is $8.00, though I think it's slightly discounted by Elderly.

I don't know of a better source on-line, and having the book precludes the electronic requirement.

The diagrams are clear, and the explanations are concise.

I wish I'd had this when I started playing, it would have saved me alot of time.

Peace. Mooh.