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MAINTENANCE MANUAL
(a)
The left EICAS computer and top EICAS display unit receive 115 Vac, 400 Hz single phase power from the left ac bus. The right EICAS computer, bottom EICAS display unit, EICAS display select panel, and both EICAS switching modules receive 115 Vac, 400 Hz single phase power from the right ac bus.
(b)
The EICAS display select panel receives 5 Vac from the master dim and test circuits for panel lighting.
(c)
Power interrupts.
1) If a power interrupt of less than 200 msec is sensed by the EICAS computer, a short term power interrupt routine is initiated. During this routine, the same pages appearing on both displays prior to the interrupt are retained. All messages retain their correct order.
2) Long term power interrupts (greater than 200 msec) are handled with a different routine as follows: a) When the EICAS computer powers up after the power
interrupt, it first determines if the other, or offside computer, is running. If it is, a request is sent for a block transfer of synchronization data. If this data is received within 2.5 seconds and all validity tests pass, power up is complete. The computer is now running with page and data from the offside computer.
b) If offside synchronization cannot be performed, the computer initializes a cold start. The computer first reads the program pins to determine if a proper and valid configuration has been selected. If not, the computer automatically displays the EICAS test page if on ground with parking brake set. If the program pins are properly configured, the computer will display the primary engine parameters on the top display unit. The secondary engine parameters will be displayed on the bottom display unit.
(6) Control (Fig. 7)
(a) Display Intensity Control
1) The right EFIS remote light sensor (AMM/34-22-00) is located on the upper side of the glareshield. The sensor measures outside ambient light intensity. An automatic dimming signal is provided by the sensor to both top and bottom EICAS displays.
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MAINTENANCE MANUAL
2) Each EICAS display receives automatic dimming signals from a local light sensor on each EICAS display. A day/night discrete is also received by each EICAS display from the master dim and test system.
3) A manual brightness control signal is sent to each EICAS display from the EICAS display select panel. Each display uses these automatic and manual signals to set intensity of the display stroke signals.
(b)
The EICAS Maintenance Panel contains no logic components and has no power inputs. A test switch and nine display control switches are located on this panel. All are single grounding discrete switches, and except for AUTO, MAN, and REC, are enabled by the air/ground relay. The AUTO, MAN, and REC switches are enabled by software, but only when one of the five maintenance pages have been selected.
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