With the increasing popularity of today's storm detecting instruments (excluding radar), and pictorial map displays, many aircraft owners are upgrading their panels and need these devices to stay aligned with the heading of the aircraft. This can be accomplished with the Century slaved NSD system by adding the Bootstrap option. Century has been making slaved HSI's for over 20 years. The Bootstrap option came about with the popularity of the RMI in the late 70's.
The Bootstrap capability in our system is developed by the 1D755 Bootstrap Slaving Amplifier. In this unit the Bootstrap capability is an actual five wire synchro output that is excited externally (normally by 400Hz 26 VAC). The 3 stator wire will be applied to the unit requiring the bootstrap.
For those slaved NSD systems that do not have the Bootstrap option, it is a simple process to change the Dual Channel Slaving Amplier (1C714) out and with minimal wiring, install the 1D755 Bootstrap Slaving Amplifier. The main connector from the 1C714 slaving amplifier (CD115) and the 1D755 are directly compatible. The minimum wiring comes into play with the slaving switch. The Slave 1/OFF/Slave 2 switch on the 1C714 is a 3PDT switch that allows the pilot to select either slave channel or a free gyro mode. Since the 1D755 is a single channel amplifier, the #2 channel wires from the 1C714 that went to the slaving switch can be removed. The #1 channel wires are removed from the slaving switch and attached directly to the NSD connector (CD111). A SPDT switch (Century P/N 40S35) is installed between pins E and K of CD111 to provide the Slave/Free Gyro switch. The additional connector on the 1D755 (CD129; Century P/N 28S66) will then be wired to the external inverter and the unit requiring the bootstrap signal.