fixing am radio?

I'm not tryin' to be mean here. If you don't know how, then you are not perfectly capable. AM radios are in some ways no different than a home AM radio. Transistors and other parts can fail, but in a vehicle, OTHER factors pop up, including water and humidity damage, mechanical and dust/ dirt damage.

There are folks who advertise to repair these. Don't know who to recommend. Because these radios are what is known as "slug tuned" they do have some fairly proprietary components in them.