Craigslist transaction went south...

I gave him the original manual with remote and calibration mic. He was saying  that the receiver does not output steady
sound. I just hooked it up and no output. After a
while it has some sound output, not a little
white later there is again none and I am unable
to get anything out. I don't know what that means.

Looks like we need Judge Judy.

Actually, I think this transaction falls into the same scenario as buying a used car. Sold "as is" with no warranty, unless you told him you were providing a warranty. As long as you knew it was working properly, you can't be responsible for what he may have done, possibly causing damage.

I spoke with him or Saturday morning. I asked him to bring the receiver to my home so that we can check this out. If it’s not working,  I would be giving his money back. So far he has not contacted me.

Do you think I need to contact him now?

Sit tight.  Unless I miss my guess, no one is suing anybody for a $120.  
If anything, possibly small claims court.  

If you don't need the drama, give the buyer his money back and be done with it ... principal notwithstanding.  

It can't be worth it at this point.  

Rich 

Hi,
Dont be afraid of legal action, facing a judge might be anxiety provoking but the judge is human like all of us. If you have done nothing wrong and explain it to the judge, judge will understand. For $125, if he hires an attorney (first, I doubt any attorney will take the case), still the court will likely award the plaintiff only $125 because you had no malice. He will have to eat the legal cost. In my experience, case like yours will most likely be decided in your favor (unless you have given guarantees of some kind, esp. in writing). Most likely, you may not hear from him again, so, relax and sleep well.
Giri