where they are converted into three-wire syncro information signals. These signals are fed back to the aircraft computer logic circuits to update the computer and develop gimbal control data bits to maintain the receiver head at the correct LOS. If the system is operating in the position mode, FWD mode, or computer track mode, and the operator wants to quickly shift to the manual track mode, the operator is able to do so by use of a manual override function on the TTSC. When manual override is initiated, a manual override command signal from the TTSC is processed by the azimuth mode logic module. This module sends a manual override signal to the D/A converter. It also sends out manual track command signals, as explained previously for manual track mode. The FLIR system functions in the manual track mode regardless of the position of the control box mode select switch. The manual track override signal disables the D/A converter. It also sends a manual track mode status to the aircraft computer logic to prevent the computer from operating should the control box have computer track selected. Elevation Drive Subsystem Figure 6-22 is the simplified block diagram of an elevation drive subsystem. Compare figures 6-21 and 6-22. Notice they are the same except for the elevation and azimuth labels on the modules. The subsystems are the same because the servomechanism elevation drive circuits operate the same and process the same signals and develop the same drive signal as the azimuth drive subsystem. The only difference is that no tachometer feedback is used in the elevation circuits, and all signals come from or go to elevation circuits vice azimuth circuits. In the FWD mode of operation, the elevation circuits slew the receiver head to –4° (down tilt) elevation. The azimuth circuits slew the receive head to 0° azimuth. All other modes operate the same except the receiver head is slewed in elevation instead of in azimuth. CS BITE Subsystem The control servomechanism BITE subsystem automatically determines whether a servo-system failure is in the CS WRA or in the receiver-converter WRA. Figure 6-23 is a simplified block diagram of the CS BITE subsystem. For ease of signal tracing, some of the modules have been duplicated at various locations on the diagram. These modules, such as the mode logic, have alphanumeric designators (A1, A2, A3, etc.). However, the modules are all part of one logic module. The alphanumeric numbers are used to show where signals enter/leave a particular module. A temperature sensor in the receiver-converter monitors the gyro operating temperature. When the gyros are operating properly, the sensor develops a temp ready signal, regardless of which operational mode is selected on the control box. The temp ready signal is fed to the mode logic module (A1) of the CS. The mode logic circuit outputs a rcvr ready signal to the servo BITE module (B1). The rcvr ready signal enables servo BITE (B1). When BITE is initiated on the control box, a BITE initiate signal is received by the servo BITE (B1) module from the power supply- video converter BITE logic module. The BITE initiate signal initiates a series of four test sequenced as follows: fault isolate, BITE 1, BITE 2, and BITE 3. All tests are controlled by a 10-HZ clock in the servo BITE module. Each test sequence takes 10 to 12 seconds to complete. FAULT ISOLATE TEST.— Initially (when rcvr ready and BITE initiate are received), the servo BITE module (B1) generates a BITE fault isolate signal and a digital computer interface (DCI) fault isolate signal. The BITE fault isolate signal goes to the following modules: azimuth position compensation (C1), elevation position compensation (D1), mode logic (A3), azimuth rate compensation (E1), and elevation rate compensation (F1 ). The signal enables all of these modules and causes the azimuth position compensation module (C2) and elevation position compensation module (D2) to generate BITE motor drive signals. The DCI fault isolate signal goes to the decoder storage module (for use in the BITE 3 test) and to mode logic (A2). The DCI signal causes mode logic to open the BITE relay drive line, de-energizing the BITE relay (shown in the de-energized position). Opening the relay removes azimuth and elevation motor drive from the motors in the receiver-converter. Instead, the azimuth and elevation heat sink motor drive output is routed to the azimuth position compensation module (C1) and the elevation position compensation module (D1). The BITE motor drive signals generated by the azimuth position compensation (C2) and elevation position compensation (D2) are routed by way of AZ POSN and EL POSN lines to the azimuth rate compensation (E1) and elevation rate compensation (F1), respectively. The drive signals out of these modules 6-21