Any metal detector breaks down, it’s only a matter of time. What is more, underwater metal detectors break down much more often than ground search ones. Here’s a step-by-step photo report: opening the Fisher CZ-21 underwater metal detector.
Remove the knobs from the controls on the detector’s front panel.
Unstick the control panel label.
Unscrew the two upper (hex) screws securing the front panel.
Unstick the two shock-absorbing strips inside the battery compartment.
Unscrew the two lower (hex) screws inside the battery compartment.
Unscrew the headphone cable strain relief. Remove the rubber gasket which provides a tight seal. Get traces of silicone sealant off the cable (so that it moves freely back and forth).
Unscrew the coil cable strain relief. Remove the rubber gasket and get traces of silicone sealant off the cable (so that it moves freely back and forth).
Pull on the detector’s front panel and take the circuit board out of the housing by pushing the panel with the coil and headphone cables.
All about the Fisher CZ-21 metal detector is collected here (photos, videos, tests, comparisons) and on Knowledgebase pages (specs, features, user manual).