AM will work to some degree with or without an antenna.
Best guess:
#1. Antenna wire not correctly connected to radio and/or antenna.
#2. Antenna cable damaged.
#3. Radio damaged.


Please look in this forum, there may be a local shop listed.

Good MB Shops
http://www.peachparts.com/shopforum/good-mb-shops/

This may help you diagnose or have it repaired.
ShopForum > Do It Yourself Links > Links by Parts Category
Accessory:
Accessory:

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