Here is another mod for 847 users by RNZ_LAB.
Rumour has it, there's sometimes a problem to set proper level of outgoing audio at DATA jack on the rear. Of course this fault is model specific, and depend on modem type as well. But there's a simple cure for it, tested myself on my FT-847.
Audio level from IC Q1102 is fed to red DATA socket via R1119 4,7kOhm.
All we need is SMD 1206type 2,2k (or 3,3k) resistor. Unscrew your radio, and set it upside down. There is red DATA socket on the rear.
Look carefully for SMD resistor marked in red circle:
Replace the resistor according to suit proper "zero" level of your output audio.
In my case replacing R1119 by 2,2k did the job FB giving 5dB more AF level..
Good luck with the mod.