Hey Jimmy,
I've got 3 tesoros and never took them apart... I guess because they just work great!
Actually, 1 of them has given up after 15yrs, but I don't want to take it apart and void my warranty.
HOWEVER, there IS info out there for you...
Directions to it are elsewhere, here on the forum, but you can just run a google search for DIY coils and a CHEMELEC will come up somewhere in there. Seems theres a bunch of really industrious guys in eastern europe that have reverse engineered some of our best metal detectors. plenty pics and circuit diagrams.
If you are unable to locate all the stuff PM me and I'll dig a url out of my bookmarks. (too many!)