Initial Inspection Of Unit; Functional Test, Standard Test Setup And Test Signal; Power On Check - Garmin GTX 327 ATC Maintenance Manual

3.3

INITIAL INSPECTION OF UNIT

If the initial bench test indicates a problem with the transponder, first remove DC power from the unit and open it
to visually inspect for damaged or loose components or evidence of heat stressed components. Visually check
each of the flex cables to verify that they are undamaged and fully seated into their connectors.
Always remove DC power to the unit before attempting to reseat any of the flex cables.
Refer to figures 7-2 and 7-3 for connector location and figures 3-2 through 3-4 for component location.
3.4

FUNCTIONAL TEST, STANDARD TEST SETUP AND TEST SIGNAL

Refer to Figure 5-1 and verify that each switch on ATC-1400A is correctly set. Unless otherwise instructed, all
standard test conditions require the ATC-1400A to be operated in Mode A, 500 Hz PRF and with an RF output of
–50 dBm. In addition, verify that the frequency/power switch is set to F
monitor "FREQ" (transmitter frequency) or "XPDR Code" (Mode A squawk information) as required. Except
when otherwise instructed, the SLS switch should be set to "OFF".
For units installed in an aircraft, adjust the power input to the unit under test to the aircraft voltage (must be
between +11 Vdc and +33 Vdc). Apply the appropriate Light Dimming voltage as used in the aircraft
installation. Refer to Figure 2–3 for test setup.
Configure the oscilloscope to monitor both the ATC-1400A interrogation pulses (GEN) and the GTX 327
detected transmitter pulses (XMTR).
3.5

POWER ON CHECK

If the unit fails the Power On Check perform the following steps:
1. Verify that either +13.75 Vdc or +27.5 Vdc is applied to main power terminal of test harness, P3271
pin 15, and AVIONICS MASTER ON, P3271 pin 1. Verify that either P3271 pin 13 or pin 25 is
connected to ground.
2. Verify that the applied input voltage is found on both sides of internal fuse F301 (3 amp fast blow) at
the rear of the main board. If proper voltage is not measured at fuse F301, replace the fuse on the
main board in the unit. If proper voltage is measured across fuse F301, check the main board power
supply voltages.
3. Verify that Q302 Collector (pin 3) is at 0 volts.
Power supply voltages may be checked at each of the following components listed in table 3-1:
Without the load of the transmitter and receiver boards, the voltages in table 3-1
can vary by as much as 15%.
3-2
Rev B
The document reference is online, please check the correspondence between the online documentation and the printed version.
/P . Use the Display Select switch to
1 1
NOTE
GTX 327 MAINTENANCE MANUAL
190-00187-05