You can get the TS690S to TX 27Mhz and RX 31Mhz 49Mhz without taking the case off.
Hold Down butons 1,2,3 whilst switching the radio on.
This opened up the Freqs Mentioned above. Also Allowing TX on 27Mhz
I didnt have time to check elsewhere but it certainly "opens " the radio up.
The next time you switch on everything is back to normal.