Connect the collector of the TX optocoupler's output transistor directly to the CI-V signal line. Connect a high-speed switching diode (such as a 1N4148) between the TX line and the input of the RX optocoupler. How it works:
Check the 1N4148 diodes—they are often soldered incorrectly. icom ci v usb interface schematic top
Draw a physical clearance gap (at least 2mm to 5mm wide) across the board. No copper traces, ground planes, or power planes should cross this line. The only components spanning this gap must be the physical bodies of the optocouplers. Connect the collector of the TX optocoupler's output