You didn't really answer the question with this reply. It doesn't matter what you did when you first purchased the amp, and it doesn't matter than you're using the FRB757 interface. Did you completely disconnect the RY and E wires from the back of the amplifier NOW? (That is, completely disconnect the FRB757 so there is nothing connected to the amp at all except the power cord for AC.) And with everything disconnected, is the amp still "keying" (relay clicks, idling current about 0.1A, etc)? If so, something inside the amp is shorting one end of the relay to ground. If not, then the problem is external to the amp and possibly the FRB757 has failed.