Like many CW guys, I hate the key jacks being on the back of rigs, especially for contests when you get operator changes who bring their own keys.
See Circuit diagram for the RF Unit(X44-3030-XX) (The front panel wiring is at bottom right).
Looking at the circuit diagram I realised that pin 6 of the mic skt was unused.
The MC60 desk mic curly lead happens to have all 8 pins wired! So, I mounted a 3.5mm socket on the side of the mic base and also a miniature push-on switch onto the flat area above the switches and below the mic boom. These are both wired between pin 6 and earthed.
By removing the bottom cover and front panel of the TS690S, you gain access to the back of the mic socket. Wire a thin 2 foot wire to pin 6, together with a .001µF disc capacitor to earth. Loom the wire back through the rig's looms and solder to the key jack, J4, P2.
After refitting everything, you will now be able to plug a key into the side of the socket on the mic platform. The small push-switch is really useful to key the TX for tuning up purposes.
CW guys will really like having the button to generate the sidetone (with the VOX off) to enable accurate netting whilst using the other hand for tuning.
I have found this to be absolutely invaluable.