1) The interrogator monitor circuits continuously monitor system performance for transmitter power output, receiver data and distance output data.
(i)
Test
1) When manual TEST is activated, the range and velocity LSI develop a synthetic reply pulse and apply appropriate distance information to the microprocessor. The microprocessor then develops the serial BCD word which is applied to the DME indicator. When the test is activated (Fig. 4), the DME indicator reads blank for 1 second, followed by dashed lines for 1 second, then followed by 000.0-nautical mile readout for as long as the test input is held LO, plus the memory time of 11 to 15 seconds.
(3) Distance Displays (Fig. 5)
(a) The DME distance displays on the RDDMI provide the pilot with slant range distance measured by the DME interrogator. The indicator receives digital data and a valid signal from the DME interrogator. The digital data is received in a six-wire BCD format. Two wires carry the 32-bit data word, two wires carry the word sync, and the remaining two wires carry the clock signal. The data decoder and shift register extract the distance data from the data word and provide the distance information to the magnetic indicator drivers.
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A 737-300/400/500MAINTENANCE MANUAL
MAN AUTO MANUAL VOR UP/LTDN/RTDME AUTO TEST NAV MAN AUTO MANUAL VOR UP/LTDN/RTDME AUTO TEST NAV DME CONTROL PANEL DISPLAY TESTMASTER DIM & TEST SWITCH (P2) VHF NAV/DME CONTROL PANEL 1 1 DISPLAY WILL ALTERNATEWHEN LIGHTS SWITCH ISHELD IN TEST POSITIONLIGHTSTESTDIMBRT DISPLAY FOR 2 SECONDSDISPLAY FOR 1 SECOND
0 0----0 0 0 0 15 FMCS SENSOR S RUDME LEFTOKFAIL L FMCS SENSOR S RUDME LEFTOK L VORDME TEST VORDME TEST CONTROL PANEL RDDMIFMC-CDU FMC-CDU 2 SEC 2 SEC DME SYSTEM SELF-TEST CONTROL PANELVHF NAV/DME-1 11.4 SEC OK 2 RDDMI PRETEST DISPLAY2 VHF NAV/DME-1 VH F N VH F N DME-1 DME-1 DME-1 DME-1 RDDMIRDDMI FMCS SENSOR S RUDME LEFTOK L FMCS SENSOR S RUDME LEFTOK L TE S T TEST VH F N VH F N FMC-CDU FMC-CDU
DME System Tests
Figure 4
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A
737-300/400/500MAINTENANCE MANUAL
(b) The drivers position the magnetic wheel indicators according to the distance information. When an absence of computed data exists the magnetic displays are rotated to their eleventh position and four white dashes are displayed. This occurs during auto tuning and when the decoder detects a NCD (no computed data) bit in the digital data word. The monitor circuit monitors the DME valid discrete input, operation of the data decoder and shift register, and the internal power supply. A loss of valid input data, or a faulty power supply, results in the red and white striped flag obscuring the display. When all functions are normal, the flag is retracted out of view.
7. Control_______
A. Power is applied to the DME system by closing the following circuit
breakers on the P6 and P18 panels:
DME 1 AC
DME 2 AC
B. Using appropriate VHF NAV control panel, tune the system as follows:
(1)
Select manual. Check MANUAL switch
indicator comes on and
AUTO frequency display
is blank.
(2)
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