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SECTION 2
TROUBLESHOOTING
2.1 TROUBLESHOOTING EQUIPMENT REQUIRED
• 0-30 Volt DC / 3-Amp Power Supply
• Digital Multimeter
• 20 MHz Oscilloscope
2.2 SELF-TEST FAILURES
The GPS 155 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
Replace Altitude Decoder Board (see Section 3.2.2)
Replace Interface Board (see Section 3.2.3)
Replace Main Board (see Section 3.2.4)
Battery rqrs service
Verify connection of external battery pack to Main Board
Replace external battery pack(see Section 3.2.6)
Course input fail
Check ARINC 429 / RS-422 course input connections
Replace Main Board (see Section 3.2.4)
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 Main Board (see Section 3.2.4)
Memory battery low
Replace memory battery (see Section 4.1)
No altitude input
Verify connections to altitude serializer/encoder
Replace Altitude Decoder Board (see Section 3.2.2)
Replace Main Board (see Section 3.2.4)
Osc needs adjustment
Replace RF/IF Assembly (see Section 3.2.5)
Replace Main Board (see Section 3.2.4)
RAM failed Replace Main Board (see Section 3.2.4)
Receiver failed
Replace Main Board (see Section 3.2.4)
Replace RF/IF Assembly (see Section 3.2.5)
ROM failed
Replace ROM (see Section 4.2)
Replace Main Board (see Section 3.2.4)
Stored data lost Replace memory battery (see Section 4.1)
* Where multiple repair actions are listed, they are listed with the most likely failure cause presented first.
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