Philips HTS-6500/37 Theater System

I service the home theater display at a major chain that has this model and every time I walk in to check on the display this model and the HTS3544 is not working. With the HTS6500 It either has no sound or the sound is distorted. It seems that this problem happens when you crank the volume up to 20 + and the audio hits some hard bass.
The HTS3544 has no sound and it does not respond when you push ANY button. The temporary "fix" is to unplug it then plug it in again.
Funny thing is that last years model,the HTS3440, had the same problem as the 6500.