If you have a spectrum analyzer, look at the receiver pass side of the duplexer, you should see the garbage come up as soon as the transmitter keys. Also if you do not modulate the repeater the garbage should be decode able with a radio such as the Kenwood TH-F6 or Yaesu VX-7 set to AM mode tuned to the repeaters input frequency. You will also see garbage on the opposite offset. if it is a 5MHz mix.
You should be able to walk around with the handheld and look at the S-meter to find the mixer.
