I've got a KR-4070 that, sometimes powers on fine. Other times everything but the tuner and signal meter light, then if you tap on the top, the light comes on. Other times when you power it on, the lights kind of flicker at almost half power with static, then a few seconds later, it all comes on. I've cleaned the main on/off switch, but still have the problem. The power switch also is the speaker A and B and AB switch. When I go from speaker A to AB, the A speakers don't come on. Should they? And if not, is the switch a problem? Thanks for the help.