INSTALLATION MANUAL
CMA-5024 GLSSU
This document includes Proprietary Information and shall not be reproduced or communicated to third party
without prior written permission by CMC Electronics Inc.
Page D.1
November 21, 2008
APPENDIX D
GLSSU TROUBLESHOOTING INFORMATION
1. OUTLINE
For installation checks and troubleshooting purposes, the ARINC 429/419 data labels to/from the
GLSSU should be observed as indicated below.
An oscilloscope should be used first, for preliminary checks of the activity, logic levels and signal wave
shapes on the busses.
If possible, use an on-board CDU to observe the activity on the busses. However some equipments or
the nature of the fault itself may preclude its use. In this case troubleshooting requires alternate access
means, such as using commercially available ARINC 429/419 data bus testers, which must be
connected physically to the GLSSU wiring at plugs J1 and J3 by means of a breakout box.
The operator should refer to the applicable aircraft operational flight manual and/or its supplement for
accessing the GPS pages of the control/display from an onboard aircraft system CDU, and to the
aircraft interwiring diagrams for wiring information. The operator should know which aircraft systems
are connected to the GLSSU, the discrete input signal settings, which ARINC 429/419 interface ports
are actually used and which ones are NOT used i.e. which GLSSU interfaces are left unconnected.
For troubleshooting the HIS device in the GLSSU and the related DME/ILS look-alike output busses,
the data source for the look-alike busses (ILS/DME inputs versus GLSSU generated GLS data) can be
selected via the ILS/GLS Source Select discrete input at connector pin J3-18. The activity on the
ILS/DME look-alike bus outputs can be monitored by means of the flight instruments in the cockpit.
The major troubleshooting activities are:
- Monitoring bus activity,
- Observing the presence/absence of specific data labels on GLSSU input busses,
- Observing and interpreting the data labels 273, 355 from the GLSSU output busses, and
- Interpretation the input/output data on other GLSSU labels.
If a wiring fault is suspected, verify the aircraft wiring as per paragraph 7 in section II herein.
1.1 GLSSU ARINC 429 OUTPUT INTERFACE CHECKS
Check the presence of the following ARINC 429 labels on the GLSSU ARINC 429 output busses at the
J1 and J3 cable connector ends.
Verify the parity bit and the SDI bits (if applicable). Verify that the data transmission rate matches the
specification for the GLS or GPS bus, as applicable. Refer to the data word formats in Appendix C.
The document reference is online, please check the correspondence between the online documentation and the printed version.
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