Ok, put my MA5100 I in queue for 1st in 3 years and the left channel is not playing in stereo. Works in mono, and when I use reverse stereo on switc as well as when I send right channel signal to both sides. Does not work when I send left channel to both sides. So, I am thinking this is a preamp issue not something in the power amp section? Unit was fine 3+ years ago after Terry DeWick upgraded it.At that point I had noise coming out of that channel. Any things to try before I have to decide on how/If to get fixed?