Hi, I emailed Dean the schematic and below is the pin data from page # 16 ts-520 manual: 1 vfo signal 2 vfo signal shield 3 ground 4 12.6 vac 5 relay voltage (+ on xmt) 6 calibrator signal (9 vdc) 7 no connection 8 internal vfo 9 vdc (jumper to pin 9 w/o the ext vfo 520) 9 external vfo 9 vdc (jumper to pin 8 w/o the ext vfo 520) 73 james ke4drn