This is what the inside of a BH/Fischer pin-pointer looks like...and some air tests I did with it apart.
There is one pot lying flat on the board (DO NOT touch the other one), and it is to control SENSitivity...
you can mark the factory position of this with a fine tip perma-marker, then tweak it to try to get a few extra fractions of an inch...
You can desolder the LED and drill a hole in the case to mount it externally (the LED comes on with the buzzer sounding)
You can also go to Rat-Shack and get a louder (beefier) 6V buzzer (It looks the same as original, but is higher Decibel Rated)
A larger Buzzer or even LED will drain the battery quicker though (But it is worth it for the added audio and light for night hunting...
These are the only 2 mods I have done to this unit...OH!!! and you can add solder to the spots the coil is soldered to...glob it on...This seemed to add some distance, if only to give better conductivity to the coil???
Be mindful of the heat, as your dealing with small parts that can burn quickly...