You can contact Keith Southern, usually find him on the Teknetics or Fisher forum now.
He will do it, I would do it in the past but, I now live up in Canada, between shipping costs
to and from me about $60.00US plus parts and labor, it's not a good deal.
Yes voids warranty but, Tesoros almost last forever anyways and generally do not need service.
Resale of a mod'd Cibola will still be as high as a used Cibola and then some will pay extra with the mod.
Those who have a V as well as a mod'd C, will tell you depth is the same or maybe better and the mod'd C
just plain is smoother and hunts better.
If your handy, you can do the mod yourself, it doesn't cost much, just have to be careful. Contact Keith S.,
you'll get it done right.
You can always adjust the GB using the trimmer pot inside the box on the PC board, that will not void warranty.
But consider it a course adjustment. An external GB 10 turn pot will get you precise tuning as well as custom tune
the GB to which size coil you switch back and forth from. You'll be able to tune out hotrocks with precision if you live in
hot rock country.
I would say add up the cost to have the C mod'd , then see if your better off selling the C and using the mod money
and apply it towards a used Tejon. Richard at Backwood's Detectors does get some deals in and may be willing to take the
C in trade towards one. Worth a look.
If you want the mod, you can download it off my website, this is the direct link to my download at Rapidshare:
click the free user button there----
http://rapidshare.com/files/394821433/cibola_ground_balance_mod.pdf