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Four Parts:Testing the BatteriesTesting the LEDs and LDRReplacing the LDRReassembling

If you have an antique stained glass solar garden LED light that no longer lights up, you don't necessarily have to throw it out. Since such lights now sell for $30.00 and up, it's worth trying to fix it yourself. Different lights might require a slightly different method, but this example project, which replaces the Light Dependent Resistors (aka photocells or photoresistors), can help you on your way.

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EditPart 1 of 4: Testing the Batteries

  1. 1
    Pull the stake out of the garden, and turn the square box over.  You'll generally find information about the batteries; for example: "2 AA Ni-Cd 600 mAh.  For best performance, replace with Ni-Cd or Ni-Mh rechargeable batteries, every year". 
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  2. 2
    Holding the top cap, carefully twist the stained glass cube counter-clockwise sliding the 4 prongs in their slots till they are released. This will expose the 2 LEDs and battery cage, under a columnar reflector.  
    • In these project, the LEDs were 600 mAh Wintonic types.
    • To test if they're working, put them in a Ni-Cd  Charger, over night, and then try them in a camera. If the batteries test okay, put them back into the battery cage.  The LEDs should light up in darkness, so if they don't, your trouble-shooting continues.

EditPart 2 of 4: Testing the LEDs and LDR

  1. 1
    Take the cover off the bottom of the cap.
  2. 2
    Using a Philips screwdriver, remove the 4 corner screws, and carefully lift off the bottom plate. Once loose, one side will resist as there are wires connected to it, that are tarred into the casing. 
    • Loosen the tar, if necessary without tension on the wires.  On this example light, the circuit board LR-79719/7296 2003-12-22 shows 2 transistors and 3 or 4 resistors, as well as a diode or 2.   One resistor, labelled R3, is close to transistor Q1.  Poking at this example with an analog multimeter set at Rx1K showed that it was connected to the base of that transistor, and has a resistance of 50,000 ohms (50KR).  It showed yellow violet orange color bars, which means it is 46,000 Ohms + or -.[1].  
    • Referring to the circuit 2 in Solar Circuits, it is the job of the Light Dependent Resistor (LDR) (aka photoresistor) to turn off the LEDs in daylight. The LDR is part of a voltage divider circuit, so a resistance of 25000 ohms can be calculated to be needed, using voltage divider calculator, for a 2 V input and a 0.7 V out at the base of Q1, a voltage that usually activates a transistor. So the LDR is not reducing its resistance to that amount or less, in daylight. 
  3. 3
    Tracing the blue wires to the LDR, punch 2 needles or sharp pins from a sewing kit, one into each wire, at the border of the bottom plate (the reason is explained later).  Touch the 2 needles/pins together; Lo!  The short circuit on the LDR turns off the 2 LEDs. 

EditPart 3 of 4: Replacing the LDR

  1. 1
    Discharge the batteries down to 1.0V or less. In other words, shine the LEDs a few days.
  2. 2
    Secure the bottom plate, upside down, or sideways to the cap using one of the screw holes, and a longer screw (or hay wire). 
  3. 3
    Take the rig into the morning sunshine, with the LEDs off via the short circuit. 
  4. 4
    Add a new LDR to the circuit from an Arduino Starter Kit.
  5. 5
    Drill 2 1/16"(2 mm) holes, 1/4" (6 mm) apart, in the bottom plate near the crossing of the blue wires and the puncture needles/pins.
  6. 6
    Ensure these holes are not covered by the stained glass cube attachment mechanism. 
  7. 7
    Thread the new LDR through from the bottom side. 
  8. 8
    Gently force the 2 prongs of the LDR through the 2 pin holes in the blue wires, one prong in each. The LEDs should turn off.

EditPart 4 of 4: Reassembling

  1. 1
    Shield the new LDR by cupping your hands over it. The LEDs should turn on in low light!   
  2. 2
    Re-assemble the detached plate, using the 4 screws.  Re-attach the columnar light reflector over the 2 LED's and batteries.  Re-attach the stake with stained glass box by hitching the prongs into the bottom plate and turning clockwise.  
  3. 3
    Set the antique stained glass solar garden light in a sunny place in the garden. 
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EditTips

  • Add a SPDT (or SPST on/off) slide/toggle switch to the new circuit, bypassing the LDR; turn off the LED's during cloudy periods, since charging of the batteries may not add enough milliAmpHour's to equal the load of the LED's; or, use it to charge batteries.

EditWarnings

  • Grasp the stained glass cube as close to the cap as possible to avoid warp of the flimsy structure.

EditSources and Citations

  1. ↑ http://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-resistor-color-code-4-band resistor color chart

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Categories: Lighting and Light Switches

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