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Page 4-12
GNS 400W Series Maintenance Manual
Rev. A
190-00356-05
Display Max Level Test
Set the display brightness to maximum and verify increased display intensity.
Display Dim Test
Vary the display brightness and verify decreased display intensity.
Keyboard LED Dim Test
Manually vary the keyboard LED backlight brightness and verify proper operation.
GPS Antenna Bias
Measure the dc voltage at the GPS antenna connector using a 35 mA load to ground. Verify that
the voltage is 4.42 to 4.74 volts. If no load is present, the voltage should be 4.66 to 4.74 volts.
Figure 4-4. WAAS GPS Status Page (Test Mode)
GPS Signal
Apply a standard GPS test signal to the GPS antenna. Let unit acquire satellite 16 and capture the
last mode 5 value prior to its transition to mode 0. Verify GPS signal A8H (42.00) to C0H (48.00)
via the WAAS GPS Status Page (Figure 4-4).
Time Mark Output
The time mark out is generated by the WAAS GPS sub-assembly. The output is a high pulse that
is used by other external units to determine when position information from the unit is valid. The
unit output pulse occurs 1 per second and is 1 ms wide. Note that ARINC 743 requires a pulse
width of 1.0 ± 0.1 ms. Verify time mark functionality using an oscilloscope and observe a 1 msec
active high pulse on J1-16.
1.
Command output high and measure output on oscilloscope. Measure at J1-16. Verify
voltage > 4 volts.
2.
Command output low and measure output on oscilloscope. Verify voltage < 0.4 volts.
