Garmin GNC 255 Installation Manual - page 69
190-01182-02
GTR 225/GNC 255 TSO Installation Manual
Rev. B
Page 6-15
6.5.4 Lighting Bus Interface Check
CAUTION
When 14 VDC or 28 VDC lighting buses are connected to the GTR/GNC, connection of
the aircraft lighting bus to the incorrect input pins can cause damage to the GTR/GNC.
Always start this test with the dimming bus at the lowest setting, and slowly increase the
brightness. If the brightness level on the GTR/GNC display does not increase as the
lighting is increased in brightness, verify that the wiring is correct before proceeding.
The display and bezel key backlighting on the GTR/GNC can track an external lighting/dimmer bus input
and use it to vary the display and bezel key backlight levels accordingly. This check verifies that the
interface is connected correctly.
1. Ensure the lighting bus is set to its minimum setting.
2. Slowly vary the lighting bus level that is connected to the GTR/GNC. Verify that the display
brightness tracks the lighting bus setting. Continue to maximum brightness and verify proper
operation.