LED strip failed.

Discussion in 'Electrics UK' started by EFLImpudence, 12 Aug 2021.

  1. EFLImpudence

    EFLImpudence

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    Does anyone know how to repair or look for what is wrong, please?

    Third brake light. 12V in on yellow wire.


    None of them is working.
    I think maybe one of the groups failed before but might be mistaken.

    upload_2021-8-12_14-25-41.png

    Thanks.
     
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  3. RandomGrinch

    RandomGrinch

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    Individual LED's can be checked by carefully putting a CR2032 3V battery across it. Make sure you get polarity correct!
    The current available from the cell is insufficient to do damage if you get it wrong!
    Hopefully this should give you an idea if repair is viable.
     
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  4. pcaouolte

    pcaouolte

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    Often a dry solder joint, possibly on one of those surface mount resistors. Apply 12v to it and then put a little pressure on each component in turn, if it starts working when you press one of the components then you have found the item which need re-soldering. They use lead free solder when manufacturing them, which is carp. The resistors can be checked with a meter and the LED's can be metered to check that they pass current in one direction only.
     
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  5. bernardgreen

    bernardgreen

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    I suspect they are not normal LEDs as there are two groups each with 6 LEDs connected in parallel. No individual current control. These LEDs probably have some type of current limiting built into the LED element.

    Do the LEDs light up in some sort of sequence, possible with a variable voltage on the yellow wire.

    The only device that appears to be common to all the LEDs is the diode at the lead end of the PCB ( in series with the black lead ) If all the LEDs went dark at the same time then I would suspect that diode.
     
    Last edited: 12 Aug 2021
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  7. EFLImpudence

    EFLImpudence

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    Thanks for replies.

    I think what Bernard says must be relevant.

    I don't know why but with testing where the voltage was going with the meter in series with the battery, I found that touching the positive meter lead (with negative on the battery) to the negative of an LED, all except the far right six LEDs illuminated. Continuing this progressively right the situation stayed like that until the far right LED negative was touched.

    This was even though there was continuity between the supply negative and this right LED negative.

    Connecting a wire between this LED negative (I suppose any would have done) and the supply negative on the light side of the diode has made all except the right six work.

    I think this must have been the situation I was vaguely remembering when one section was out previously.

    I don't pretend to understand what happened.

    upload_2021-8-12_18-54-31.png
     
  8. Swwils

    Swwils

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    Often these "center high-mounted stop lamp" are not driven by discreet components anymore but one IC like a TPS92610 to save on cost / wiring.
     
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  9. EFLImpudence

    EFLImpudence

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    It's just a direct 12V supply from the fuse via brake pedal switch.
     
  10. EFLImpudence

    EFLImpudence

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    Thanks for that.

    Touching any of the LEDs lights that group, but no luck on the group of six which remains not working.
     
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