Some interesting connectivity choices were made on these models, none of which are the standard connections.
The audio in and out (but without PTT) can be found on 3.5mm TRS labeled “DATA IN/OUT”, the serial CAT as well as PTT is on the MiniDin6 socket labeled “CAT”. The serial port appears to be using logic levels (5V).
I have tried to make the cables as described above. So far I haven’t succeeded with the serial MiniDin6 cable, but still work on it. The audio cable with one modification has worked for me. I connected the 3.5mm TRRS audio ring2 (PTT) with a separate wire and a phonoplug/RCA plug to the PTT jack. This works for me, (but of course it doesn’t control the frequency).
After further checking I have now made both cables (Audio and Serial) work as described above at the beginning. Initially I didn’t see that the two cables had to be interconnected. When that was done it worked using settings from a FT-920 as described under “Cable for Yaesu FT-900”. In addition I also found it important to use Baud rate 4800 under Radio Control Port.
Thanks for something that now works perfect.