12VAC garden LED lights, burnt out components, anyone skilled enough to guess what they were?

Discussion in 'The Projects Forum' started by flappa, May 8, 2016.

  1. flappa

    Thread Starter New Member

    May 8, 2016
    6
    1
    Hi
    Hoping someone can help. I have attached a diagram of the circuit inside a rather expensive stainless steel garden light. So it's worth trying to fix it.
    It was damaged by an over voltage and two components on the internal circuit board were burnt out.

    What appears to be a 1w resistor and a very small diode (1N914 / 1N4148 size). The transistor cracked open but I could identify it as per the diagram.

    It's a 12v AC input light fitting with about 30leds. The internal circuit board converts the AC to 5V DC

    Any ideas anyone?
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It looks like you switched pinnames in your schematic.
    The correct pins are these:

    MJE13003_pinout.png

    The diode in the circuit will likely be a zenerdiode of about 5.6 Volts

    Bertus
     
  3. flappa

    Thread Starter New Member

    May 8, 2016
    6
    1
    Hi Bertus,

    The Transistor is a TO 92 package and it's the 'B' > 13003B. apparently from online spec sheet it's as per my diagram.
    I have uploaded a picture of the PCB. The Diode is on the other side.

    Any guesses on the resistor? I'm only assuming the output is 5v DC. And it's exactly 30 Superbright LEDS

    Thanks
    Frank
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Is it possible to post a photo of the top and bottom of the led board?
    Then we can see how the leds are connected and estimate the needed voltage.

    Bertus
     
  5. flappa

    Thread Starter New Member

    May 8, 2016
    6
    1
    Hi Bertus,

    Not possible, it's silicone sealed into the head of the tube fitting out of reach. It took some careful and painful work getting the PCB out from the underside without damaging the rest. I see what you are getting at. I'm thinking I'll have to pull apart another working unit to determine the resistor value and read the output voltage. What I was trying to avoid, but I may have no choice?

    Frank
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    On the powerboard there is a connector to the leds.
    Do you have a adjustable powersupply?
    Watch the polarity, it is given at the plug on the powerboard.
    If so, you could start at a low voltage and turn the voltage up, until the leds are at the brightness you are used to.
    The reached voltage must be made with the powerboard.

    Bertus
     
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  7. flappa

    Thread Starter New Member

    May 8, 2016
    6
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    Hi, I'll get my hands on an adjustable power supply and see how I go...thanks Bertus for your advice so far.
    It may be a couple of days before I can attempt it.




    +10 GMT
     
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  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I would start at about 3 Volts and slowly turn the voltage up.

    Success.

    Bertus
     
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  9. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    particulary bad circuit

    Use a stepdown dcdc module, increase the voltage carefully.
    You could measure the current, it will be wrong with DMM a bit.
    If it is normal LEDs 15mA or so is enough.

    throw away the bad PCB...
     
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  10. flappa

    Thread Starter New Member

    May 8, 2016
    6
    1
    Hi,

    So I have identified the Resistor to be 150ohm and the output is actually 12vDC (I resorted into pulling apart a working unit)
    So can I assume the diode is a Zener of 12volts?

    Frank
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Could you measure the AC input voltage?

    Bertus
     
  12. flappa

    Thread Starter New Member

    May 8, 2016
    6
    1
    Hi,

    The input is specified as 12v AC. The output from the working circuit is 12v DC.
    I have used a 12v Zener and now all is working fine on the repaired unit. I ended up using a BD639 to replace the transistor.
    Brightness matches the working unit.
    I'll make sure I don't feed in the incorrect voltage next time!!

    Thanks for all the suggestions and discussions of help folks.

    Problem solved.

    Frank
     
  13. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    @flappa
    An other option would be the use of an 7812 voltage regulator with 2 capacitors:

    3-pin_low_power_regulators_with_capacitors.png

    Bertus
     
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