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14

2.4

TROUBLESHOOTING CHART

MESSAGE

RECOMMENDED REPAIR

Unit will not power on

Check External Power Connection

Check Remote External Battery Pack (if equipped)
Check Pwr/Volume Switch Connection
Replace Pwr/Volume Switch (see Section 3.2.7)
Replace CPU Board (see Section 3.2.4)

Unit will not power off

Replace CPU Board (see Section 3.2.4)
Replace Pwr/Volume Switch (see Section 3.2.6)

Display has horizontal
or vertical lines

Replace Display Board (see Section 3.2.8)
Replace CPU Board (see Section 3.2.4)

Display has missing or
dark pixels

Replace Display Board (see Section 3.2.8)

Display brightness not
adjustable manually

Replace CPU Board (see Section 3.2.4)
Replace Control/Display Unit (see Section 3.2.1)

Display brightness not
adjustable via photocell

Replace Control/Display Unit (see Section 3.2.1)
Replace CPU Board (see Section 3.2.4)

Keycaps have no
backlighting

Replace Control/Display Unit (see Section 3.2.1)
Replace CPU Board (see Section 3.2.4)

Keycap backlighting not
uniform

Replace Control/Display Unit (see Section 3.2.1)

Bezel Annunciators 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 operation in Test Mode
(see Section 4.2.3)
Replace CPU Board (see Section 3.2.4)

Keycaps do not function
properly

Replace Control/Display Unit (see Section 3.2.1)
Replace CPU Board (see Section 3.2.4)

Dual concentric (rotary)
knobs do not function
properly

Check Flex Circuit connection from rotary switch to
back of Control/Display Unit
Replace Rotary Switch Assembly (see Section 3.2.7)
Replace Display Board (see Section 3.2.8)
Replace CPU Board (see Section 3.2.4)

Approach arm switch not
functioning properly
(300 only)

Check connections and verify operation in Test Mode
(see Section 4.2.3)
Replace external switch
Replace CPU Board (see Section 3.2.4)

Sequence Hold  low
switch not functioning
properly (300 Only)

Check connections and verify operation in Test Mode
(See Section 4.2.3)
Replace external switch
Replace Comm Chassis Sub Assy (see Section 3.2.2,
steps 1-7)
Replace CPU Board (see Section 3.2.4)

GPS reception weak or
GPS Status Page shows
low  signal levels

Replace Antenna and/or antenna cable
Replace GPS Receiver Board (see Section 3.2.5)

Содержание GNC 250

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

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

Страница 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...

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

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

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

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

Страница 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...

Страница 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...

Страница 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...

Страница 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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