WSAH 194 FM radio stop working


I bought this kit for my son and it worked for a while. It stopped working for no reason, it no longer receives FM stations, only noise is heard.
I read on the forum that it could be a problem in the MM110, but I can’t purchase it separately.
How can I buy buy spare parts? The store will not give me a replacement product because the radio is assembled, they only change unused products.