Craigslist transaction went south...

Hope everyone is doing great. I have a situation here and I am hoping you guys can help. 
I have sold a home theater receiver to someone. We met at gas station and everything went fine. It happend on Sep 4th.  Today (Sep 15th)  i got a text from the same guy saying he just installed and the receiver is not working. He is going to take legal action against me. it was working receiver and i never had any problems with it. I don't know what to do now. . I am legal immigrant and working on visa.  Please advise.
Here is my ebay profile:

Thanks Guys. I took your advice and talked to him. I asked him to bring the receiver to me and I am going to give his money back. 
If you are refunding make sure he is returning the receiver you sold, not his broken one that is the same model.
In followup to jmcgrogan2's post, the situation of someone receiving working equipment but then claiming it was defective by swapping in another similar but nonworking item can easily be avoided.  Every sale should include a bill of sale to prove legitimate purchase.  The bill of sale should include the item's serial number or other identification.  If the transaction is face to face, as was the OP's, then the seller should bring a copy of the bill of sale and have the buyer sign it as a receipt to be kept by the seller.  If the transaction is by mail, the bill of sale can be included in the box.  In addition, the seller should take pictures of the item to show its physical condition in case of dispute about that, and one of the pictures should be of the serial number.
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I don't have a bill of sale. Even it he brings his broken one, I am going to give his money back as Dave and Rich said  "It Is not worth the hassle."