Having installed a synchronous detector board into my R71a, there was the need to select between it and the original AM detector, without defacing the radio by adding extra switches to the front or rear panel. After studying the circuitry around the mode select IC13 on the logic unit board, there is an unused pin 1 that can be used for this task. Remove Diodes D10 and D13 from pins 32 and 36 on IC14. Add a long wire to pin 1 of IC13, best done at the unused pin at J2. This wire will now go high when FUNCT/CW is pressed, .... the same way as FM is selected by pressing FUNCT/AM. For my situation, I routed this wire through to the main board, through a switching diode, cathode to AM pin on J12. This enables AM mode when high. The added`wire also connects to the base of Q25 through a series 4k7 resistor, and a switching diode, cathode to base. This disables the normal AM detector when high. The voltage on this wire also is used to enable the Synchronous detector board. In use, all mode functions are as normal, pressing FUNCT/AM will select FM, AM will select normal AM, now pressing FUNCT/CW will select the new Synch AM, The ICOM memory will also store the new synch mode together with frequency. Unfortunately, there is no spare or unused icon in the flourescent display to activate with the new mode, so when selected, no mode icon is visible. This switching arrangement has many other uses and saves having to mess up the appearance of the radio. When working on your radio, take your time, and understand what you are doing. Disconnect power first.