Hello, i sent my concert sound cassette out to be rebuilt. Wired it in and worked fine. Now, a day later cassette volume is extremely low. Fm and aux volumes are fine. Fade and balance work on all. I put a pair of kenwood 4 ohms in the back which are working fine..all others are stock. Display clock, memory all ok... any suggestions what might have happened would be appreciated. My only thought is : the car is hooked to a 6amp charger could it have damaged the amp (separate amp for cassette?) Do these systems have protection mode?