+ AA6YQ comments below
I sent the message below to the WSJT-X group looking for help with control of my old IC-375A. Since I hope to run that rig via DX Commander I am sending the message to the DXLab group as well to look for help here.
I recently obtained a old 1980s-era Icom IC-375A monoband 222 MHz transceiver, and I cannot get it to work with WSJT-X. The first problem is that there is no IC-375A Radio option in the WSJT-X settings menu, so there is no direct way to control this transceiver from WSJT-X. I had partial success by selecting "DX Lab Suite Commander" as the radio and using DX Commander to control the CAT portion of the interface since DX Commander does have an IC-375A option. With that setup I can control the IC-375A frequency and mode from DX Commander, and both DX Commander and WSJT-X properly display the chosen mode and frequency. FT8 reception works, but PTT and audio TX do not work. I'm using the default IC-375A CI-V parameters Hex12 and 1200 baud.
My interface is a G8XGG "USB-DIGIMODE-4" box with three cables: USB to computer, ACC DIN connector to rig, and CI-V cable to the rig's 3.5mm mini "REMOTE" connector. This interface presents both an audio CODEC and a COM port to the computer.
It's worth noting that the ancient IC-375A does not have a CAT command to control PTT, so that function must be performed separately from the CAT link (via RTS on the COM port). The rig will be operated in USB mode since there is no dedicated digital mode on the IC-375A.
+ Have you arranged for the COM port RTS signal to switch your IC-375 from RX to TX and back? Does this work correctly?
+ Have you configured the Audio tab of the WSJT-X Settings window's Audio tab to use the virtual soundcard sections presumably created by your "USB-DIGIMODE-4" box for Input and Output?
+ Have you configured the Windows multimedia mixer to provide a sufficient level on the virtual soundcard's Playback section?