Text of Kenwood Sheet on using Cross Band Repeat on the TM-731A:

The repeater corss-band operation allows the TM-731A to receive on one band and re-tramsmit the signal on the other band. An incoming signal will automatically be switched to the sub-band. The TM731A will then re-transmit the signal from the main band. Each band may contain shift information. Only one band can contain sub audible tone information (the optional TSU-6 ... currently called by Kenwood the KQT8... is required for tone decode). If one band requires a sub-audible tone, either select the TONE function for encode or the CTCSS function for encode / decode. DO NOT turn both TONE and CTCSS on in the one band.
Select the first frequency in the main band. If required, select the offset.

Press the BAND key to move the contents of the main display to the sub-display.

Now select the second frequency and offset.

If Tone or CTCSS is required for one of the bands, continue with this step. If Tone or CTCSS is not required, go to step 5.

Place the operating frequency that requirs TONE or CTCSS in the main band (use the BAND key).

Select the sub-audible tone by pressing the F key and then the T.SEL key. Rotate the main encoder knob until the desired tone is displayed. Press any front panel key to display the operating frequency.

If only the TONE function is required, press the TONE key (the [T] indicator will light in the display).

If the CTCSS function is required, do not turn the TONE function on. Instead, press the F key and then the CTCSS key (the [CTCSS] indicator will light in the display. If the CTCSS arrow is not pointing towards the main display, press the F key and then press the CTCSS SEL key. 

Adjust the main and sub-band squelch controls to the threshold point. The TM-731A will transmit in the repeater cross band mode if the squelch controls are set too low or a signal is received. (comment: setting both squelch controls properly is VERY important!)

Note:
The next step will place the unit in the repeater cross-band mode

Press the F key and then press the A.B.C. key. Three dots should be lit in both display frequencies. The unit will now operate as a cross band repeater as described above.

To take the TM-731A out of the cross-band repeat mode, repeat step 6.