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9

SECTION 2

TROUBLESHOOTING

2.1

TROUBLESHOOTING EQUIPMENT REQUIRED

· 

0-30 Volt DC / 6-Amp Power Supply

· 

Digital Multimeter

· 

20 MHz Oscilloscope

· 

Adjust Power Supply to 14 Volts

2.2

SELF-TEST FAILURES

The GNC 250/300 monitors many of its internal functions and displays a message to alert the user
should a failure occur.  The table below shows the recommended repair for each self-test failure
message.

MESSAGE

RECOMMENDED REPAIR*

Altitude input fail

Verify connections to altitude serializer/encoder
Verify connection between CPU Board and Comm
Receiver Board
Replace comm  chassis sub-assembly
Replace CPU Board

Course input fail
(300 only)

Check ARINC 429/RS422 course input connections
Replace CPU Board

Data card failed

Replace NavData® card
Replace Interface Board (see Section 3.2.3)

Data card write fail

Replace user data card
Replace Interface Board (see Section 3.2.3)

Fuel/Air input fail

Check connections to fuel/air data system
Replace CPU Board (see Section 3.2.4)

Memory battery low

Replace memory battery (see Section 4.1)

No altitude input
(300 only)

Verify connections to altitude serializer/encoder
Verify connections between CPU Board and Comm
Receiver Board
Replace Com/Chassis sub-assembly (see Section 3.2.2)
Replace CPU Board (see Section 3.2.4)

Osc needs adjustment

Replace GPS Receiver Board (see Section 3.2.5)
Replace CPU Board  (see Section 3.2.4)

RAM failed

Replace CPU Board  (see Section 3.2.4)

Receiver failed

Replace CPU Board (see Section  3.2.4)
Replace GPS Receiver Board (see Section 3.2.5)

Stored data lost

Replace memory battery (see Section 4.1)

Configuration reset

Replace CPU Board (see Section 3.2.4)

EEPROM write fail

Replace CPU Board (see Section 3.2.4)

Summary of Contents for GNC 250

Page 1: ...g f g h e f e e g g e e e he he g he g e e e g g he g g he e e e he he g he e C e e e e C e C he g e C he e e e e e e e e B e e e B B e e e B e e e e e e e e e e e e e e e e e e e e e f e B B g B e e...

Page 2: ...RES 9 2 3 INITIAL TROUBLESHOOTING OPERATIONS 11 2 3 1 Power Supply Check 11 2 3 2 Internal Clock Check 11 2 4 TROUBLESHOOTING CHART 14 2 5 TROUBLESHOOTING COMM SECTION 16 SECTION 3 DISASSEMBLY INSTRUC...

Page 3: ...RAM 5 FIGURE 4 RF IF BLOCK DIAGRAM 7 FIGURE 5 COMMUNICATION TRANSCEIVER 8 FIGURE 6 CPU BOARD TESTPOINTS TOP VIEW 12 FIGURE 7 CPU BOARD TEST POINTS BOTTOM VIEW 13 FIGURE 8 COM RECEIVER TEST SETUP 35 FI...

Page 4: ...es in manufacturing technology In order to achieve the desired reliability size and power requirements surface mount components are used extensively Specialized equipment and procedures are required t...

Page 5: ...14VDC Converter Contains circuitry for converting 28V power bus to 14V in 28V aircraft 1 2 DETAILED DESCRIPTION Internally the GNC 250 300 is divided into seven printed circuit boards the CPU GPS Rece...

Page 6: ...3 Figure 1 GNC 250 300 Block Diagram...

Page 7: ...by 20 column unit with variable intensity This display provides excellent day and night visibility from wide viewing angles The front panel provides function selection and alphanumeric input to the C...

Page 8: ...5 The block diagram in Figure 3 below shows the interaction between the various CPU board circuits Figure 3 CPU Board Block Diagram...

Page 9: ...ear connector J1 and from the AC adapter through a DC power jack located near the rear connector External battery pack power is also applied to the rear connector J1 All of these sources are diode iso...

Page 10: ...nications Transceiver The VHF communications transceiver consists of the comm receiver board assembly and the transmitter board and casting assembly The VHF receiver is a single conversion super heter...

Page 11: ...r using microphone input via the J2 connector to collector modulate the final two stages of the transmitter through power transistor Q34 The microphone circuits contain a compressor which limits the A...

Page 12: ...card Replace Interface Board see Section 3 2 3 Data card write fail Replace user data card Replace Interface Board see Section 3 2 3 Fuel Air input fail Check connections to fuel air data system Repl...

Page 13: ...onnection between CPU Board and Comm Receiver Board Replace comm chassis sub assembly see Section 3 2 2 Replace CPU board see Section 3 2 4 Remote ENT key stuck Verify that remote enter input to unit...

Page 14: ...515 and ground as shown in Figure 7 The voltage should be between 17 00 and 67 00 volts If the voltage is out of the limits specified replace the CPU board 4 Check the DC voltage between L504 and grou...

Page 15: ...12 Figure 6 CPU Board Testpoints Top View...

Page 16: ...13 Figure 7 CPU Board Testpoints Bottom View...

Page 17: ...nunciators do not function Replace Display Control Unit see Section 3 2 1 Replace CPU Board see Section 3 2 4 No external annunciator output s message arrival approach Check connections and verify ope...

Page 18: ...output Replace CPU Board see Section 3 2 4 No external CDI output or external CDI functions improperly Check connections and verify operation in Test Mode see Section 4 2 3 Replace CPU Board see Sect...

Page 19: ...at all times Verify connection between Control Display unit and CPU Board Verify connection between CPU Board and Comm Receiver Board Replace Control Display unit Replace comm chassis sub assembly se...

Page 20: ...odulator transistor Q34 and from Q34 to transmitter Verify connection between CPU Board and Comm Receiver Board Replace comm chassis sub assembly see Section 3 2 2 steps 1 7 Replace modulator transist...

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