Ensure the SKK-620C is correctly grounded 

In a dual–master station system, a loud feedback sound is heard at both master stations. 

This can be caused by a common power supply and/or missing DAK-2S. If both C-ML/A master stations share the same power supply, a ground loop feedback will occur when the talk button is pushed. Install separate SKK-620C power supplies or install batteries for each master station. The DAK-2S “Dual Master Component Modules” must also be installed per the wiring diagram below: 

Communication timeout issues 

If the resistance of the wire is too large, usually from exceeding distance limitations, the master station may not time out as designed.

22AWG = 245′ 

18AWG = 490′ 

Communication volume is too loud or too soft 

It’s possible the volume control is not adjusted properly. Remove the front cover of the C-ML/A and locate the volume potentiometer through a hole located at the bottom of the station. Use a small screwdriver to adjust the volume; clockwise to increase, and counterclockwise to decrease. Do not turn the potentiometer too hard in either direction or damage may occur.