The CZ20 was introduced in 1995 by the "old Fisher". It was a pretty good machine at the time, but over the years they forgot how to calibrate the darn thing (very complicated calibration procedure), they forgot the things that were necessary to keep it from leaking under water pressure, and finally the company that manufactured the pinpoint switch stopped making it. The plastic tooling and user interface circuitry were designed around that particular switch.
It was no longer possible to repair a CZ20 to its original condition. In fact, not even the Old Fisher could repair a CZ20 to its original condition: they didn't know how and they didn't have the materials on hand to do it anyhow.
When the old Fisher finally went belly up because almost nobody wanted their products any more, FTP in El Paso purchased the assets. One of those assets was an underwater machine platform that once upon a time had worked right. That meant it was fixable, but it took us a couple years of figuring out all the problems and solving them to bring the thing back to the 1995 standard. It came at huge cost in plastic tooling to accommodate a new and different scuba-rated pinpoint switch, and to solve the leaker problems. I still don't know whether rescuing the damn thing was a good idea or a bad idea.
We can't refurb CZ20's because the materials to do it no longer exist, and in many cases the fact those materials no longer exist is a good thing. However, inasmuch as we manufacture the CZ21 which is by most accounts a very good product, we can convert a CZ20 to CZ21 specifications. Some of the CZ20 stuff is usually still salvageable, it depends on what lands on our receiving dock. Rather than try to negotiate with each customer a price to change over his or her particular machine, the factory declared a fixed price for the conversion, it's either yes or no.
The CZ21 circuit design, insofar as it impacts performance, is exactly the same as the original CZ20. Which is the same as the original CZ-6 in saltcomp mode as introduced late 1991.
*****************
The CZ series have provoked a lot of discussion hereabouts. I began development of multifreakers within weeks of my hire with Fisher in 1981, and the CZ platform was fielded a decade later. Here we are more than 2 decades later still making the things. The other "old Fisher" thing we still make for the consumer market is the GB2, introduced 19 years ago. Every consumer market product introduced by the Old Fisher since that time has been discontinued because customers decided they didn't cut it.
For the last 33 years, I have been the engineering design philosophy behind the Fisher trademark. Things went to hell during my over 10 years furlough but the philosophy that kept the Fisher trademark alive during that hiatus is still here. I fight for every hour of battery life, I fight for the basics of detection technology, I fight for simplicity of user interfaces so the customer can actually deploy the benefits of the technology, and I fight for no piling on of expensive and mostly useless "features".
