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737-300/400/500MAINTENANCE MANUAL
(2)
Display Unit Overtemperature
(a) The analog deflection signals are sent to the deflection yoke in the CRTs. A temperature of greater than 75°C in the deflection circuits generates an overtemperature discrete, which is transmitted to the symbol generator. This will remove the raster display from the CRTs within 30 seconds, at which time the message WXR DSPY will be annunciated on the EHSIs. If the temperature of the deflection circuits rises to 100°C, the entire CRT display will be shut down. The rise in temperature from 75°C to 100°C normally takes a minimum of 90 minutes. If the temperature of the deflection circuits decreases to less than 70°C, the raster display on the CRTs will be restored.
(3)
Loss of Cooling Air
(a)
The symbol generators receive cooling from the Equipment Cooling Exhaust System (21-58-03). When cooling exhaust air is lost, a discrete from an airflow sensor illuminates an equipment cooling supply off light as well as the master caution lights.
(b)
The display units (DUs) receive cooling from the Equipment Cooling Supply System (21-58-02). When cooling supply air is lost, a low air flow sensor in the cooling duct provides a discrete signal to the symbol generators. The symbol generators immediately lower the refresh rate for stroked characters displayed on the DUs. In addition, the DU raster display will be inhibited within 30 seconds. This removes the weather radar display from the EHSIs, and also removes the sky-earth ball from the EADIs. The removal of the raster display causes a WXR DSPLY annunciation on the EHSIs.
25. EFIS BITE and Test Displays___________________________
A. EFIS BITE
(1)
The integrity of the EFIS system can be thoroughly checked using FMS BITE. The FMS BITE allows the EFIS to be checked for inflight faults, ground faults, current faults, and the status of the discretes associated with the system.
(2)
In-flight faults pages provide a historical record of faults detected during nine recent consecutive flights. The record is stored in nonvolatile memory (NVM) within the FMC.
(3)
Ground Faults pages are used to check the presence of any faults that occur while the airplane is on the ground. The record of the ground faults is stored in a dedicated nonvolatile memory (NVM) within the FMC.
(4)
Current status pages are used to check the present status of all EFIS components and the systems that interface with the EFIS.
B. EFIS Self-Test
(1) A self-test of the left or right EFIS can be initiated by actuating the TEST switch on the left or right EFIS symbol generator. Pressing the TEST switch causes test patterns to be displayed on the EADI and the EHSI. These test patterns are displays that are simulated within the symbol generator and are not dependent on the operation of the interfacing systems. The patterns can be observed to quickly determine the operational status of EFIS.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH EFIS ú
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737-300/400/500MAINTENANCE MANUAL
(2) The EFIS BITE can also be used to initiate simultaneous self-test of left and right symbol generators.
C. For complete coverage of EFIS BITE and EFIS Self-test refer to the FMS BITE (Chapter 22-07).
26. Operation_________
A. Functional Description
(1)
The EFIS symbol generator performs all monitoring, signal interfacing, signal processing, and display generation necessary for system operation.
(2)
Signal Interfacing
(a) Various airplane systems provide analog, discrete and digital ARINC 429 inputs to the EFIS symbol generator. The symbol generator also receives ARINC 453 digital data from the weather radar system, and discrete signals from the EFIS control panel.
(3)
Signal Processing
(a) The processor circuits within the symbol generator perform the following functions on the input data: 1) Check for presence and validity of data on all digital
input data buses.
2) Condition and filter selected ARINC input data and discretes. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：737-300 400 500 AMM 飞机维护手册 导航 NAVIGATION 1(120)
