After posting the first message, I phoned Fisher in Los Banos and spoke to Don Parks, who very cordially explained that Fisher has found the source for the recurrent problem.

Apparently there is a faulty programming chip in the unit. Fisher was not aware of the problem the first 3 times. They are now aware of it. I hope this can be some help to other CZ-7A owners who are having problems with the sensitivity going belly up!

I should have gotten more info. I don't know if this faulty chip is endemic to all CZ-7As or if only a few have the problem.

I thought the detector was out of warranty. I checked the warranty card and date of purchase was 2-5-99. WHEW! I lucked out there. I immediately boxed it up and sent it to Los Banos after speaking to Mr. Parks. Out of warranty repairs can run up to $135 dollars per hour depending on detector. I don't know precisely what Fishers rates are, but I would guess they are fairly high. I insured it for $800 bucks. Hmm, I wonder if Fed Ex will lose it? :))

In all fairness, I've found a lot of stuff with this detector. It's got it's quarks like all brands do. I bought it because of it's waterproofness and long battery life. Having a detector you can use in the rain is a big plus. I like detecting in Winter months on the California Coast. Digging in wet ground is easy and depth seems to be several inches more as opposed to dry summer conditions. The parks are also free of crowds and many that charge in summer are free during winter.