Cheap eBay LED tester fixed

Found this from eBay for about 2 dollars: New Mini Handy 2~150mA LED Tester Test Box for Light-emitting Diode Bulb Lamp

Description:

  • 100% brand new and high quality
  • Material: Plastic
  • Color: White
  • Handy device for testing LED’s. Simply plug your LED into the correct holes (all of which are marked) and push the button to see its brightness, illuminant color, etc.
  • Handy device for testing LED’s (2-150mA)
  • Simply plug your LED into the correct holes (all of which are marked) and push the button to test its brightness, illuminant color, etc
  • The top row is for 2 pin LED’s with currents ranging from 2mA – 30mA
  • The bottom row is for 4 pin LED’s (piranha LED’s) with currents ranging from 20mA – 150mA
  • Lightweight & compact
  • Powered by a 9V battery (not included)
  • Item size(L*W*H) : Approx. 8 x 5.5 x 2.2cm / 3.15″ x 2.16″ x 0.87″
  • Quantity: 1PC

 

Something wrong. LEDs get power at opposite polarity compared to what is printed to front panel. Let’s look what is inside.

Let’s look closer to the circuit. There seems to be one board with switch + LED + resistor. The other board contains a set of resistors that limit the current coming to the specified current. Because those are just resistors, the current will vary somewhat depending on the LED voltage (higher the LED voltage lower current it gets).

It seems that there is polarity mixup here. What start on power switch board as red wire from battery ends up being connected to black wire to LED test connector board.

Fixed

Now everything works as planned.

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