Strange noises from an A-720

Sometimes it works fine. But sometimes it remains silent after I turn it on. When that happens for a soft, pulsing sound, like a running motor, is audible from the power transformer area. I shut it off immediately when this happens of cours. DC at the speaker terminals is .001 and .005 volts. Thanks.

Never mind. It turned out to be the push on connector on one of the little boards attached to the heat sink.