"Repair" mystery

Discussion in 'General Electronics Chat' started by BobK, Jan 8, 2017.

  1. BobK

    BobK

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    This year, for the holiday season, the lovely wife Morticia and I put these nifty LED candles in each window of our house. They have a flickering LED "flame" on top, two AA batteries, a switch on the bottom. The bulb screws into the candle shaft and has a circle in the middle of the bottom that contacts the + battery terminal, and an outer ring that contacts a loop of wire coming up the shaft when screwed in fully. They are nifty because they light for 5 hours from the time they are first turned on, repeating every 24 hours.

    But we have some cramped passages in our house, and walking past the windows often knocked the candles off. Three of them ended up not working after taking a fall. Both Morticia and I tried taking them apart removing the batteries, replacing them and reassembling multiple times and we could not get them to light. These are new this year, and all of the contacts were clean and shiny.

    So I took them upstairs to the lab for diagnostics. I set my bench supply to 3V and touched leads to the bulb of the first one. It lighted. So I connected my multimeter to the battery terminal and outer terminal and it read 2.8V. I reassembled the candle, and voila, it worked! Second candle exactly the same procedure and it worked again.

    I now had a theory that the circuitry somehow got in a funny state that it would not come out of with 2.8V but would with 3.0V, so I set out to test this theory on the third candle. Just to make sure once again that it was not the disassembly / reassembly that fixed them (the obvious first guess), I redid this a couple more times with the third candle. Then, I thought I would check the voltage before applying a voltage from the lab supply. This one checked out at 2.5V. Now, I reassembled and, to my amazement it started working.

    I can't help but think it is still the multiple disassembly / assemblies that fixed them. But three of them each working only after checking the voltage seems a bit too coincidental.

    Any ideas?

    Bob
     
    BobK, Jan 8, 2017
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  2. BobK

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Is the timing magic in the bulb? Child of have decided it was an off time?
     
    (*steve*), Jan 8, 2017
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  3. BobK

    BobK

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    The timing starts when they are powered on and they repeat the 24 hour cycle as long as power is maintained. If you switch them off and on, the timing is reset.

    Edit: Interestingly the timing appears to be crystal accurate. We powered them on in sequence then placed them in the windows so the came on one at a time from left to right then bottom to top, about 10 seconds apart, and this order continued over multiple days.

    Bob
     
    BobK, Jan 8, 2017
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  4. BobK

    shrtrnd

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    I'm thinking like *steve*. Something in the timing/on-off circuitry.
    Knocking them to the floor dislodged the batteries WHILE they were in their timing mode.
    Then just reinserting the batteries confused them.
    I think it'd be something in the design. Turning them on and off, but not considering in the design phase
    what would happen to a disruption in the battery power during their operation/timing mode.
    You asked for ideas. That's mine.
     
    shrtrnd, Jan 9, 2017
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  5. BobK

    BobK

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    No, I can take the batteries out and put them back in all day long and it will reset the timing correctly. Except it did not do so for the 3 candles that had fallen and gone off. So there is some difference there. I can see that a very short interruption when the hit the floor and the mechanical shock disconnected power briefly might put them in some odd state, but how could that persist after removing the batteries? And what got it out of that state in the end?

    Bob
     
    BobK, Jan 9, 2017
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  6. BobK

    shrtrnd

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    Are you sure these were Christmas decorations? ....
    Wait a minute. These were probably made in China. I'll bet they were the same circuit as their Halloween
    devices.
    BobK. If you don't have Ghosts From Christmas Past working here, you've got left-over spirits from Halloween at work.
    You're probably going to have to wait until you knock them off their perch next year, to try continuing troubleshooting this problem.
     
    shrtrnd, Jan 9, 2017
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  7. BobK

    BobK

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    Well, Morticia agrees whit you. She believes in the magic smoke theory. The falls released the smoke, and my multimeter doubles as a smoke injector.

    Bob
     
    BobK, Jan 9, 2017
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  8. BobK

    shrtrnd

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    Kinda puts a crimp in your own magical troubleshooting and creative abilities.
    Maybe a séance is in order here.
    Remind the beautiful Morticia that you DID make them work again.
     
    shrtrnd, Jan 9, 2017
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