I have a Kenwood TS-570D which was used by a friend. When I got it back his call was recorded in CH1 and other responses in CH2 and CH3. How do I erase what is in those channels? I never use them because I have a memory keyer. The manual tells how to record, but not how to erase what is recorded. Thanks in advance. Jim, K4TXJ Louisville, Ky.