A small early batch of the Mach 3 shipped out with incorrect markings. The FX Send and FX Return are reversed. If you switch the cables then the amplifier will operate normally. 

If you would like a replacement label to cover the Send and Return so that they read correctly, open a Support Ticket at the top of our Support page. In your message, please include your serial number and address. From there, we will mail a label for you.