GTX 327 MAINTENANCE MANUAL
Page 3-3
190-00187-05
Rev. B
Table 3-1. Main Board Power Supply Voltages and Tolerances
COMPONENT
VOLTAGE
TOLERANCE
Q309 Collector
+54.0 Vdc
±
2.0 Vdc
Q310 Emitter
-5.1 Vdc
±
0.2 Vdc
D308 Cathode
+14.45 Vdc
±
0.75 Vdc
D309 Cathode
+5.1 Vdc
±
0.2 Vdc
D310 Anode
-12.0 Vdc
±
0.25 Vdc
D306 Cathode
+63.0 Vdc
±
2.5 Vdc
3.6
MAIN BOARD ASSEMBLY
If problems are discovered with any of the main board power supply voltages, disconnect the flex cables to the
receiver and transmitter in order to isolate the problem to the main board or one of the board assemblies.
Replace the main board assembly if any of the following conditions are true:
•
While the unit is receiving valid interrogations, pulses appear at receiver TP2 and main board I204
pin 64 but not at main board I204 pins 58, 59 and 60.
•
Main board power supply voltages are not correct while receiver and/or transmitter is disconnected.
•
There are no LCD pulses at I204 pins 67-70 when the unit is powered on.
•
Valid altitude inputs are present at J3271 but there are no altitude pulses transmitted in Mode C.
3.7
DISPLAY ASSEMBLY
Perform the following key matrix test to isolate problems to either the front display assembly or main board
assembly. The key matrix test, Table 3-2, states the points to check for testing the front panel keys. The column
and row points are identified on the main board diagram, Figure 3-2.
With no front panel buttons depressed, key columns are normally pulled high to +5 volts. Key rows are low but
are sequentially strobed high by the XILINX chip at a 25 mS rate. When depressed, a key column becomes a low
signal that is pulsed high coinciding with its respective key row strobe.
1.
With no buttons depressed, verify that key columns 1 through 5 are not pulled low.
2.
Referring to main board assembly drawing Figure 3-2, depress each front panel button and check for
coinciding pulses at the appropriate key and row location referenced in Table 3-1.
For example, attach scope probes to both key columns 1 (R218) and key row 3 (J103 pin 18). Sync
to key row 3 and observe both channels. All key rows should have 30
µ
S wide, high going pulses at
a 25 mS rate. With no keys depressed, all key columns should be high. Depressing the VFR key will
drive key column 1 low except for high going pulses that coincide with the strobe of key row 3.
The document reference is online, please check the correspondence between the online documentation and the printed version.