Wiki

AM only and AM/FM radios contain a number of tuned circuits which are adjusted by the manufacturer to the same frequency or frequencies by means of trimmer capacitors having an adjustable screw head, or by coils (often in an aluminium can) with a ferrite core that can be screwed in or out. DO NOT adjust these - you need specialist equipment and the service handbook for the particular radio in order to do so, without which you are very likely to make the radio much worse rather than any better. As a last resort, having understood how a superhet works, adjust one at a time, noting the exact position of the screw head before the adjustment and returning it to the same position if there is no significant improvement. If you succeed in making an improvement, make sure the improvement is maintained across the tuning dial.