As it says in the Technical Support FAQ, this message indicates that the Argus is NOT RECEIVING any RS-232 data from the NAV Receiver. Unlike the other messages, this one has a single cause: There's nothing there! There are four possible reasons for this lack of data:
First, confirm that this is the problem. REPLICATE the reported symptom. There are other LRN DATA messages, and this information applies ONLY to the "LOST" variant. Nobody reading this will be surprised to find that sometimes messages that leave a screen as precise patterns of illuminated phosphor can turn to "I think it said" when reported by the operator.
There are two keys to solving this problem - knowing what was done last, and using your trusty oscilloscope.
If the system NEVER worked, i.e., if this is a new installation, the first thing to check is whether the NAV receiver is transmitting data. Many receivers have to be configured to send data, and some of them must be configured as to which port to transmit on and what format to transmit, e.g., ARINC or RS-232. First, confirm that the receiver is configured to send RS-232 data on the port that is wired to the Argus input. Once you are sure you have accomplished this, use an oscilloscope to check the RS-232 output terminals on the NAV receiver and confirm that there is data present. Next, check for data at the Argus input connector, pins 4 and 16. Note that it is insufficient to confirm that the HOT lead only is connected. The Argus has an isolated (ungrounded) input and both the data and ground lines MUST be connected for the Argus to function. If you are convinced that there is data present at the Argus input and you still receive the message, remove the Argus from the tray and connect it to bench power, and connect RS-232 from a computer to the Argus. The data format and content are irrelevant - the Argus just tests for the line being toggled. If there is still no response, the Argus may be defective.
If you have recently had the NAV receiver repaired, replaced, exchanged, or upgraded, then you should check the RS-232 configuration as described above. Confirm that it is configured to send the correct data, and use your oscilloscope to confirm that there is actual data on the output pins.
If you have recently had the Argus updated, upgraded, replaced, or had the battery changed, then the most likely cause is that the Argus has not been properly or firmly inserted in the mounting tray. We have seen this a number of times! The Argus can be a tight fit, and if the attachment screws at the top of the Argus aren't loose enough when you insert it, it can seem to be fully inserted when it's not. Ideally, when you insert it, you will feel the resistance of the socket when it is close to fully inserted, and a firm and satisfying thunk as it travels the last fraction of an inch (cm) to bottom in the connector. Even if you truly in your heart believe the Argus is fully inserted, take it out, loosen the top two screws so that the Argus goes in with little resistance, and derive a frisson of joy from the knowledge that when you feel the final bottoming of the connector you will probably have solved your problem.
If this is not the cause, look for bent connector pins or anything that may have been disturbed while the Argus was being serviced. Again, you must use an oscilloscope to confirm that data is present on the Argus pins.
If the system failed for no apparent reason, i.e., it was working OK and the pilot reported a "LRN DATA LOST" message, then any of the problems listed above could be the cause, and you will need to trace the signal from the NAV receiver to the Argus input with your 'scope.
Here are simple instructions for doing a bench check of the Argus to confirm that the input circuit is working.
This page created 21 April 2005
This page updated 19 January 2006