Static or Mains Hum

If you use the unit’s serial interface port, make sure there is no ground loop between your control interface and audio. Usually there is a “lift ground” switch on the control unit that breaks the ground loop.

Also, make sure the input and output snakes run close together.

The chassis is connected to the unit ground via the power supply board. Over time, this connection can weaken or break, resulting in excessive mains hum or interference from the digital circuitry inside the unit. To test the ground connection check resistance between any metal part of the chassis and the ground trace on the capstan motor. If the ohmmeter shows open circuit or resistance in excess of 1 Ohm, then the chassis grounding connection is likely compromised.

To restore the grounding connection, remove the screw outlined in the picture above and clean the pad underneath, then reinstall and tighten the screw (make sure not to apply excessive torque, as the thread in the aluminum heatsink is easy to strip). You may also need to tighten the two screws that attach the power supply heatsink to the chassis.