My suggestion is to measure the DC voltage going to the pot.It is usually found on the two outer pins. The center is almost always the wiper assembly. The way the pot works, is as a variable voltage divider feeding a diode that changes reverse capacitance as the voltage fed to it is changed. You need to replace the pot with a D to A chip. They are cheap and pretty easy to use. An 8 bit chip will give you 255 steps between 0 and 5 volts or so. A higher res chip will give you smaller increments and finer tuning but may have some noise issues and is more difficult to program. With the cheaper receivers, the unit is "tuned" with a pot because there is little frequency stability, and it is cheaper and lots easier than a fractional N synthesizer. The down side to replacing the pot is that step "55" which originally corresponded to channel 1, may not take you back to the exact frequency after a few hours of use. It should be a fun project, and will reward you with alot of knowledge if not a satisfactory product.

Ron