Garmin 155XL Maintenance Manual page 21

3.5 TROUBLESHOOTING
Table 3-2 contains problem/action information to aid in troubleshooting the GPS 155XL Perform the actions in
the sequence they are listed.
Unit will not power on
Unit will not power off
Display has horizontal or vertical lines
Display has missing or dark pixels
Display brightness not adjustable
manually
Display brightness not adjustable via
photocell
Keycaps have no backlighting
Keycap backlighting not uniform
Bezel Annunciators do not function
No external annunciator output(s)
(message, arrival)
Keycaps do not function properly
Dual concentric (rotary) knobs do not
function properly
3-6
Table 3-2. Troubleshooting Chart
PROBLEM ACTION
Check External Power Connection
Check Remote External Battery Pack (if equipped)
Check Power Switch
Replace Power Switch (see section 4.3.7)
Replace CPU Board (see section 4.3.5)
Replace CPU Board (see section 4.3.5)
Replace Power Switch (see section 4.3.7)
Replace Display Module (see section 4.3.9)
Replace CPU Board (see section 4.3.5)
Replace Display Module (see section 4.3.9)
Replace CPU Board (see section 4.3.5)
Replace Control/Display Unit (see section 4.3.2)
Replace Control/Display Unit (see section 4.3.2)
Replace CPU Board (see section 4.3.5)
Replace Control/Display Unit (see section 4.3.2)
Replace CPU Board (see section 4.3.5)
Replace Control/Display Unit (see section 4.3.2)
Replace Control/Display Unit (see section 4.3.2)
Replace CPU Board (see section 4.3.5)
Check connections and verify operation in Test
Mode
Replace CPU Board (see section 4.3.5)
Replace Control/Display Unit (see section 4.3.2)
Replace CPU Board (see section 4.3.5)
Check Flex Circuit connection from rotary switch to
back of Control/Display Unit
Replace Rotary Switch Assembly (see section 4.3.8)
Replace Display Module (see section 4.3.9)
Replace CPU Board (see section 4.3.5)
190-00067-25 Rev D