PA-28R Dim Gear Light

Discussion in 'Maintenance Bay' started by iamtheari, May 16, 2019.

  1. iamtheari

    iamtheari Pattern Altitude

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    In my Piper Arrow (the original Hershey bar wing, 180hp version), the left main gear indicator light is dim, maybe 1/4 the intensity of the other two lights. Moving the bulbs around keeps the dim light at the left main position. Turning on the nav lights dims all three indicators further, so I don't think it's somehow failing to undim the left main light. I have not noticed any flicker or other weirdness.

    Other than pulling all new wires to diagnose with my checkbook, does anyone have suggestions for causes to rule out?
     
  2. gkainz

    gkainz Final Approach

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    corrosion in the left main bulb housing?
     
  3. iamtheari

    iamtheari Pattern Altitude

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    Could be. I suppose the way to rule that out is a multimeter at the housing to check if there's 12V at that point with the master switch on, and to compare resistance to the other two housings with the master switch off.
     
  4. bnt83

    bnt83 Final Approach PoA Supporter

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    Swap light bulbs from one to another?
     
  5. iamtheari

    iamtheari Pattern Altitude

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    Did that already. The dim light is whichever one you put into the left main socket.
     
  6. Skip Miller

    Skip Miller En-Route

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    First step would be to clean the metal contacts in the dim light circuit, and look for corrosion in the connections to that bulb. It is too easy to get a false resistance/voltage measurement when your contact is the pointy end of the multimeter probe. -Skip
     
  7. iamtheari

    iamtheari Pattern Altitude

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    I trust my multimeter more than my eyes. My theory is that, if the multimeter shows full voltage at the socket, it means that the socket is the problem and I have ruled out the rest of the circuit (wire and microswitch). But I will also try to look in the socket for corrosion or other contamination and give it a squirt of contact cleaner for good measure.
     
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  8. mondtster

    mondtster Pattern Altitude

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    Skip has a point, although the way he wrote it may be too subtle unless you’re pretty familiar with electricity and troubleshooting. Unless you test the full functioning circuit full voltage at the socket may not mean much since there is no load.
     
  9. iamtheari

    iamtheari Pattern Altitude

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    Good point, thanks. I'm mostly trying to find objective metrics I can use to rule out likely causes without needing an expert eye to make subjective judgment calls.
     
  10. bnt83

    bnt83 Final Approach PoA Supporter

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  11. frfly172

    frfly172 Touchdown! Greaser! PoA Supporter

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    try a simple application of contact cleaner.
     
  12. Doug Reid

    Doug Reid Pre-takeoff checklist

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    Voltage and current are two different things. You can sometimes read correct voltage when the connection is so poor no reasonable current flows. Think of a piece of stranded 20 gage wire..maybe 24 strands in the wire but all are broken at the connection except for one. Voltage is read as normal, but not enough current carrying wire there to do any type of work.
     
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  13. JAWS

    JAWS Line Up and Wait

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    Get the maintenance manual for your aircraft . Find the correct wiring diagrams for your serial number. Figure out the possible places that could cause a poor connection, starting from easiest to check and most likely.

    My money is on a connector or switch that comes in contact with wind, moisture, etc. Wheel well, gear leg, cowling. As I recall, those switches are pretty Mickey Mouse affairs.

    Might be best to jack the aircraft for safety before touching. Don't want to wear the piper.
     
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  14. iamtheari

    iamtheari Pattern Altitude

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  15. luvflyin

    luvflyin Final Approach

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    Has it always been that way. Or did it just start doing that? If you adjust the panel dimmer does it change it's intensity at all?
     
  16. iamtheari

    iamtheari Pattern Altitude

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    It started suddenly, but not recently. See my earlier 2017 thread that @Spring Ford found. Same thing, I just haven't figured it out yet. The panel dimmer has no effect on it, other than the fact it dims proportionally with the other two lights in the well-known Piper Arrow "crap my gear isn't going down!" effect of turning on the nav lights. That is, all three lights have two settings. High and low. And the affected one is also both high and low, but both settings are much dimmer than its neighbors.
     
  17. Spring Ford

    Spring Ford Pre-takeoff checklist

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    On second thoughts. I have been having a quick look at the schematics for some random PA-28R.

    Under NO CIRCUMSTANCES troubleshoot this with the electrical system live.

    One wrong move and the gear could retract.

    The indication system is of course intimately bound with the actuation system

    You should probably leave this to a professional.
     
  18. luvflyin

    luvflyin Final Approach

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    Gotcha. It isn’t what I thought it might have been then. Good luck tracking it down soon.