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TROUBLESHOOTING CHART (cont.)
Display brightness not adjustable
Replace Pwr/Dimmer Switch (see Section 3.2.7)
Replace Main Board (see Section 3.2.4)
Annunciators &
Keycaps have no backlighting
Replace Control/Display Unit (see Section 3.2.1)
Replace Main Board (see Section 3.2.4)
Keycap backlighting not uniform Replace Control/Display Unit (see Section 3.2.1)
Annunciators do not function Replace Control/ Display Unit (see Section 3.2.1)
Replace Main Board (see Section 3.2.4)
No external annunciator output(s)
Check connections and verify operation in Test
(message, arrival, approach)
Mode (see Section 4.3.2)
Replace Main Board (see Section 3.2.4)
Keycaps do not function properly
Replace Control/Display Unit (see Section 3.2.1)
Replace Main Board (see Section 3.2.4)
Dual concentric (rotary) knobs do
Check wiring harness connection from rotary switch
not function properly
to back of Control/Display Unit
Replace Rotary Switch Assembly (see Section 3.2.8)
Replace Control/Display Unit (see Section 3.2.1)
Approach select switch not
Check connections and verify operation in Test
functioning properly
Mode (see Section 4.3.2)
Replace external switch
Replace Main Board (see Section 3.2.4)
OBS select switch (“course select”
Check connections and verify operation in Test
or “hold”) not functioning properly
Mode (see Section 4.3.2)
Replace external switch
Replace Altitude Decoder Board (see Section 3.2.2)
Replace Main Board (see Section 3.2.4)
GPS reception weak or GPS Status Replace Antenna and/or antenna cable
Page shows low signal levels Replace RF/IF Assembly (see Section 3.2.5)
No GPS reception
Check Date/Time Page for correct UTC time
1
Check Position Page for close approximate starting
position (within 300 nautical miles)
2
Replace Antenna and/or antenna cable
Replace RF/IF Assembly (see Section 3.2.5)
Replace Main Board (see Section 3.2.4)
Unit displays velocity when not
Replace RF/IF Assembly (see Section 3.2.5)
moving
3
NiCad battery life is short Replace External Battery Pack
or NiCad battery inop Replace Main Board (see Section 3.2.4)
Unit loses memory in spite of new
Replace Main Board (see Section 3.2.4)
memory battery
Unit does not detect low battery Replace Main Board (see Section 3.2.4)
10