# # Wiring Notes - - March 2010 # 990C-3D Shelf and the 514A series Control Heads # In our application, we are using 671A-4's as receivers and not as receiver-exciters. Since we do not have the amplifier coupler installed, we are missing the ground on the coupler fault line. The receiver will not provide an audio output unless the fault lines are clear. What you get is audio that is a series of "beeps". To remove the fault condition (the missing amplifier-coupler), a ground is placed on Pin "i" of J1 of the 671 mounting shelf. In our case, we use the 990C-3 shelf. We added a section of wire from the J-1 connector to a spade connector which is then grounded. Later, we will add a small switch to provide a way to enable or disable the bypass function. We will not modify the 990C-3D shelf. The J3 connector on the mounting shelf is not used. It is normally used to connect to a Selective Call decoder (such as the Motorola version). In addition, in some limited aircraft installations, this connector is also connected to the additional tuning capacitor. Please also see the notes on the 514A-7 Control Head. While not we are not using 514A-7's to control all the four (4) 671's we have, we wired the interconnection harness to support using any control type of control head. Kevin