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 En-Route

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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. 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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  13. iamtheari

    iamtheari Pattern Altitude

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  14. 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?
     
  15. 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.
     
  16. 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.
     
  17. 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.
     
  18. iamtheari

    iamtheari Pattern Altitude

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    Contact cleaner and insert/remove bulb a half dozen times seems to make it shine equal to the other two lights when the panel lights are off. When they are on, it still looks dimmer (as in the other two are barely visible and the problem bulb appears off), but that's in a lit hangar. Once the annual is done, I'll have to fly with it during the day and night a bit to see if there is a real improvement or not.
     
  19. Arrow76R

    Arrow76R Pre-Flight

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    Since you swapped bulbs, and the problem stays with the left main bulb, I suggest that the left main "down lock" switch could be bad resulting in a high resistance circuit from the 12 volt bus to the bulb. The microswitches for the gear are sealed but they do age (like all of us). You might check that BUT, as the OP stated, do it with the plane on jacks just to be safe!! upload_2019-6-17_17-59-6.png
     
  20. iamtheari

    iamtheari Pattern Altitude

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    Thanks for the diagram. Is the ground on the bottom of that diagram (through the resistor) or the top? If I were designing it, I would put it at the top and ground the switches to a common point in the wings to save on wire weight.

    My thought now is that, assuming the contact cleaner did not fix the issue, I can measure the resistance from the bulb socket to ground, a path which would be nothing but wire and one switch, and compare the left main to the right main and nose. Since the light has been consistently dim, not flickering (at least not flickering slowly enough for the eye to discern), this should at least narrow it down to the side of the circuit between the bulb and ground. And that's something I can easily test in the plane with the master switch off. No need for jacks.

    If I narrow it down to the switch, I can write it up for my next annual so it can be done when the plane is already on jacks.
     
  21. Arrow76R

    Arrow76R Pre-Flight

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    Yes, I agree with your plan. The "low side" connection of the socket is through a fixed resistor when nav lights are ON or direct to ground via the nav light switch if nav lights are off thus making the lights dim when nav lights are on.
     
  22. iamtheari

    iamtheari Pattern Altitude

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    So, I had it backwards and the switches connect to positive voltage on their common terminals, which complicates things slightly. But it's still a workable plan. And I am thinking about changing out or short-circuiting that stupid resistor while I'm at it...I wonder if I can find an IA to sign off on that. I've never been landing at night and thought to myself "I am sure glad those gear indicator lights are extremely dim, that really inspires confidence!"

    But basically I can leave the panel light switch off and test the following resistances:

    A - Left neg to ground: should be close to 0
    B - Right neg to ground: should be close to 0
    C - Nose neg to ground: should be close to 0

    D - Left to nose: should be close to 0
    E - Left to right: should be close to 0
    F - Nose to right: should be close to 0

    If A, B, C, and F are all 0 and both D and E are significantly above 0 and similar to each other, then I will have isolated the problem to the left main switch and its wiring. If all of these are indeed close to 0, then the bulb socket is the most likely culprit. (Although I really do suspect the switch since it lives out in the elements, gets an oily bath if the strut leaks fluid, and otherwise has probably had a much rougher life than the bulb socket over the past 50 years.)

    It looks like switches are reasonably priced in airplane terms:
    https://www.knots2u.net/switch-down-limit-main-gear-piper-67411-04-67411-004/
     
  23. Arrow76R

    Arrow76R Pre-Flight

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    Agreed although it might also be the "handshake" connector for the downlock switch wiring. Located on the gear itself. You might check that too. It is usually covered with some type of plastic tubing that protects the connector but I suppose it could have become corroded, etc.
     
  24. iamtheari

    iamtheari Pattern Altitude

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    I finally got around to measuring the resistances. All three bulb socket negative sides measure 0.1 ohm or less resistance between each other. The nose and right bulb socket positive sides measure low or no resistance between each other. The positive side of the left bulb socket measures 220 ohms to either of the other two bulb sockets. So the bulb and socket are eliminated from contention, and we can say with certainty that the problem is in the positive side of the circuit for the left bulb. Next step might be to soak the switch down in contact cleaner and go up to cycle the gear a few times.

    What is the ‘handshake’ connector?
     
  25. Arrow76R

    Arrow76R Pre-Flight

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    The "handshake" connector looks kind of like a pair of scissors in that the two ends close down on each other. They are used on the gear switches on my Arrow and are covered with clear tubing the ends of which are tied tightly to keep (or minimize) moisture, grease, etc.

    [​IMG]
     
    Last edited: Jun 30, 2019
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  26. LTAPilot

    LTAPilot Filing Flight Plan

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    I'm having the same problem except it's the nose wheel light that is very dim. Did you find the problem with yours? Thanks! 1969 PA-28r-180
     
    Last edited: Jul 18, 2019
  27. iamtheari

    iamtheari Pattern Altitude

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    No solution yet. I did spray the switch with contact cleaner before my last flight, no improvement. I'll do that a few more times before I give up and order a new switch.
     
  28. LTAPilot

    LTAPilot Filing Flight Plan

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    Thanks Iamtheart, If you find something, Please post it, and I'll do the same thing. I've also sprayed the socket and it didn't make any difference. The nut on back of the socket is loose, but the other day I didn't have anything to tighten it up with. I hope to trouble shoot it more this Sunday and Monday. Best of Luck!
     
  29. LTAPilot

    LTAPilot Filing Flight Plan

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    Hey Iamtheari, I posted on Facebook PA-28 page and got a couple of responses that I've copy and pasted here, Maybe this will help us both: From A.S. Had this happen to me, with the light getting dimmer and dimmer over time. Problem went away when we replaced the gear switch. From L.Hunt,, Had the same problem. Retract the gear and right gear light would stay on but would be dim. A&P tried to clean the switch but this last annual had it replaced. No more problem. I guess I'll try and get a new switch
    and have it replaced this week.