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Your wiring probably needs to be:
Pin 1 at CNC connected to cable shield, and no connection at other end.
Pin 2 to 2
Pin 3 to 3
Pin 7 on CNC to pin 5 at computer
jumper 4 and 5 at the CNC
separately jumper 6, 8, 20 at the CNC
Use a real RS232 port at the computer and not a USB adapter.
Try 9600 baud, 1 stop bit, even parity, and XON/XOFF handshake.
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