Missing lateral guidance..sometimes

Discussion in 'Avionics and Upgrades' started by Skyrys62, Feb 1, 2021.

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  1. Skyrys62

    Skyrys62 En-Route

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    Issue:
    #1 NAV/CDI intermittently has no lateral navigation when tuned to VOR - fed from Garmin 430w
    No issues with #2 NAV/CDI - fed from old ARC unit
    #1 CDI works for ILS, (even when the VOR won't) so guessing the CDI is ok?
    And that being the case, doesn't appear to be antenna cable/connection issue?

    I've got a coupler/triplexer like in the below picture, under the panel. Cleaned the connections and it seemed to help when powering up the G430w, and checking the OBS reading. Wasn't able to fly at that time though, but thought it was fixed.
    A few days later, no OBS reading again on boot up. Messed with cables again, and after a few times, got OBS reading again. Rebooted, gone again.
    Taxied out to fly, during runup, checked, and had OBS reading again.

    I found some older threads that mention this issue, but mostly speak of issues with the G430w itself, or the CDI, but none mention this device.

    I thought about switching the cables on the NAV coupler....understanding that it could appear to work due to the intermittent connectivity. However, if the problem then moves to #2 NAV, I have found the culprit (seemingly).
    Or, is there a reason I shouldn't try this?

    In my mind, this triplexer seems the least likely candidate.
    Anyone see issues with one before?



    [​IMG]
     
  2. Ryan Klems

    Ryan Klems Pre-takeoff checklist

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    The likelihood of that being any part of issue is pretty low, but sure go ahead and swap the two nav ports. It's a passive component, so there really isn't much of anything in there to fail, but corrosion and vibration can take their toll.

    However, depending on what you mean by "no OBS reading on startup", I can pretty much guarantee it's not the issue. If you are literally referring to the 430 showing what the reading of the OBS is on its display at startup, that circuit doesn't even have anything to do with the antenna. If you mean you can't play with the OBS and get the needle to move around with a known VOR signal, then would potentially be a signal issue. You can boot the 430W in to config mode (hold ENT while powering on the unit), then rotate the small right knob until you get to the instrument panel self test. The watch the OBS field while you rotate the OBS on your CDI. Ensure that there doesn't appear to be any dead spots and that it matches with the display. You can recalibrate the OBS if needed by setting it to 150 then hitting cursor and rotating the big knob until you get to the OBS field and it should offer something like 'Calibrate 150?' and you can press enter to recalibrate (It's been a bit since I did that so I may be missing something, but it should be relatively obvious). If the OBS is dropping out, it's likely a CDI or wiring issue, though could also be an internal issue with the GNS430W, but it's not going to have anything to do with nav signal.
     
  3. Skyrys62

    Skyrys62 En-Route

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    I am referring to the OBS window in the 430. I called an avionics shop not too far away and spoke with this gentleman at length. He said when you boot the 430 you should have an OBS setting showing. And when you rotate it should change. However about 75% of the time there is no OBS reading. He said that would indicate typically a loose connection of some sort. I cleaned the connections and it's still intermittent. The last two times I flew and actually tuned to VOR it had no lateral guidance. But I did not check the OBS at that point as we were flying.
    I have also removed and reseated the 430 in the panel three times trying to clean connections very gently each time.
     
  4. Ryan Klems

    Ryan Klems Pre-takeoff checklist

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    Yeah, so that OBS circuit is 6 wires (3 shielded pair) between the indicator and the unit and doesn't need any VOR signal to be read. You could have the antenna completely disconnected from the 430W and you should still be able to read the OBS resolver value from the CDI. What indicator do you have connected to the 430W? You might try reaching up behind the panel if you can and try to push slightly on the connector going in the back of the indicator and see if it moves in at all and if that makes any difference.
     
  5. Skyrys62

    Skyrys62 En-Route

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    Ryan, looks like you were right on.
    After much contortion I was able to barely reach the back of the indicator, but could not see it. It does seem that it's the culprit, either a break in a wire or the connector is loose-ish.
    Time to remove the G430 and tray I reckon...unless there are other ideas on how to tighten it up?
     
  6. Ryan Klems

    Ryan Klems Pre-takeoff checklist

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    If it's the connector at the indicator, you hopefully shouldn't need to touch the 430. What indicator do you have, GI-106? Depending on the indicator, the connector and its attaching/latching mechanism is different. The GI-106 uses a squeeze locking mechanism that you squeeze to push on or to pull off and if you don't get the connector fully seated before you let go, it doesn't securely latch on both sides and can potentially back out slightly on one side. You could probably unscrew the CDI mounting screws from the panel and slide it back and down, allowing you to get a better look at it and try re-seating the connector. Or just take it to the shop :)