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Sandel SN3500/4500 EHSI and Garmin Automatic NAV Source Switching Feature
Contributed By:
Mark Everhart, Techinical Support Representative
Most dealers are aware that the Sandel SN3500/4500 Primary Navigation Displays and the Garmin 400/500 WAAS and non-WAAS series (excluding the GNS480) have an automatic switching feature. This allows the Garmin unit to switch to the same NAV source selected with the Sandel unit’s NAV button and the Sandel unit will switch to the same NAV source selected with the Garmin unit’s CDI button. This feature works using switching bits within label #100 Selected Course on the Garmin GPS 429 bus and the same label on the Sandel 429 bus back to the Garmin. For this feature to work properly the Sandel and Garmin units have to be configured properly, the 429 buses must be wired correctly creating the loop between the 2 units, and the Garmin has to be locked on to satellites with a “Direct To” to some waypoint 30 miles or greater.
Most of you may have noticed that when this feature does not work correctly the Sandel unit reverts back to GPS1 when trying to select NAV1. I would like to outline the configuration and troubleshooting procedure to resolve this problem. This configuration is addressing the automatic switching feature only.
Sandel SN3500/4500 configuration:
1) Maintenance Page 7 GPS-1 (Same for GPS-2 dual install):
A) Select Garmin GNS 430 (ARINC) for all GNS430/530 units
B) Select Garmin GNS 500 (ARINC) for all GNS400/500 units with no NAV receiver installed. This selection tells the Sandel to ignore the switching bits.
C) ARINC-429 line = Select the proper 429 input bus speed whether high speed or low speed. (Depends on the installation).
D) The Sandel 429 output bus is low speed and is on at all times. No configuration is necessary.
Garmin 400/500 series configuration:
1) Main ARINC 429 configuration page
A) In 1 = Low, Sandel EHSI
B) Out = Low/High (Depends on install) GAMA 429 Grph w/ INT
C) SDI = LNAV 1 if Garmin #1. LNAV 2 if Garmin #2.
2) Main CDI/ OBS configuration
A) Make sure the CDI selection can be changed on this page with the CDI button on Garmin 430/530 units. If it cannot then the unit has been configured to lock the CDI button to GPS only. This function must be unlocked for automatic switching to work.
After the configuration has been verified make sure the wiring is correct per the Sandel installation manual.
The Garmin GPS must be locked on to satellites with a “Direct To” to some waypoint 30 miles or greater.
If at this point you are still having problems contact Sandel product support.
Note: If the SN3500 has software 3.05 loaded it will not switch the Garmin unit. However the Garmin unit will still switch the SN3500 unit properly. An updated version of software will be released soon.
For any questions please contact us.
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