spiralsupward

I own an Sony MZ - RH1 with an apex 162 mini stereo condensor microphone. Lately there has been a level of hum on the microphone during recording that has made it impossible to use. The problem used to occur only when using outlet power, now it seems to happen all the time. I have replaced the microphone with a new one, but the problem persists. Does anyone have any suggestions? I love this recorder and dont want to throw away a $400.00 piece of equipment for something so simple. C.