I want to control a RX-A1060 mute function via it's RS-232c connection.
To send the serial commands I am using a Hall Research HR-4 [Link: hallresearch.com] with null modem cable between the devices.

I am doing something wrong because after working on it for several days I cannot get the 1060 to respond.

To MUTE the receiver I am using the serial command of:
"@MAIN:MUTE=Off" without the quotes

I have confirmed that the HR4-P is sending the above command by using Termite. [Link: compuphase.com]

Port Settings:
Baud rate : 9600
Data bits : 8
Parity : No
Stop bit : 1 bit
Handshaking : None

What am I forgetting or doing wrong?
Thanks, Allen