Autohelm Inboard Autopilots (ST6000 and ST7000 systems) Service ...

Autohelm2.2. Reverse Connection ProtectionTR1 and TR2 along with RL1,2 and 3 ensure that external misconnection of Heavyduty V+, Heavy duty 0V and M1 and M2 will not damage the unit.2.3. Bridge AmplifierTR6, 7,8 and 9 form a bridge amplifier to control the actuator motor. Four modes ofoperation are possible, each selectable with a binary code on drive A and drive B.Mode 1 - Drive A and drive B both a logic 1. The motor is shorted via TR7 and TR9.This mode is used for stopping the motor quickly.Mode 2 - Drive A and drive B both at logic 0. The motor is open circuit and thereforemay run as a generator allowing measurement of motor back emf. R14 and R16 incombination with R25 and R28 on the computer PCB scale down the back emf.Mode 3 - Drive A is at logic 1. Drive B is at logic 0. The motor will rotate clockwise.Mode 4 - Drive B is at logic 1, drive A at logic 0. The motor will rotate anti-clockwise.TR4 and TR10 are interlocks, switching off TR8 and TR6 when both drives areswitched high in mode 1. C3 and C20 suppress motor brush noise.4SeaTalk Service Manual