I have a problem with my H/U... Alpine CDA-7873. front end and subs running off amp, rear off H/U. The problem is.. front left has no sound at all, under heavy load front right cuts out intermittantly (with bass mostly). I have tested my patch cords, all good. amps are fine as well. I have no idea, I hope it's the head unit as I love it and have had it for a long time now.. any help would be great!

 

Did you check your connections at the speakers?
I am assuming that you have the front hooked up to an amp. See if the amp is putting out power for the front left.

 

I have meter'd everything at low volume. NOW I have found that I am losing power to my front end amp. NOT a H/U problem as I first thought! Now it's a wire problem, I presume I am losing ground but that is just a guestimate until morning when I can take a look at it!

 

I found the answer, Somehow the tab for the connections on the driver door mid broke off and was hitting the basket.