Repair - Multi-purpose Fault finding method

Here I'll show you a fault finding method which will cover all types of light bulb and LED strings. It uses low cost test equipment and the normal power supply for the lights. It is based upon sound electrical theory and many examples are given.

Method 3: Divide & Conquer

The principle is to connect a resistor to bypass about 50% of lights in the suspect group and see if the remaining group of lights glow when light string is energised.

How does it work: the resistor makes a parallel path to the bad light bulb/ LED and electricity can flow in remaining 50% of lights which obviously light up (the red line in the string below shows the current path.). This process is repeated until the bad light is found.

This is a very simple, quick method which works for all type of light bulb or LED strings... whether the bulbs/ LEDs are open or shorted; mains power or low voltage lights, AC or DC, 10 or 200 lights. For a 50 light series string, after 4 tests you will narrow it down to 3 possible bad bulbs!

Here's a detailed example of how to use this method. The photo shows the red resistor lead is plugged into back of plug.

  

 

 

Yes it's this simple to find a bad bulb or light fitting.

 

Resistors fitted with 3 metre lead + crocodile clip each end (to suit):

–12V LEDs – 2 of 1200 Ω 1/2W connected in parallel (= 600Ω)

–24V LEDs – 1 of 820 Ω 1W

–120V LEDs – 1 of 5,000 Ω 10W

–120V bulbs – 3 of 2,000 Ω 10W connected in parallel (= 666Ω)

(You will have to make the ones you want. Cost about $5 each for materials)

 

•Hint: it’s good to practise these techniques upon good strings where you can easily remove a bulb/ LED to make a fault. Then find it!

 

NEXT >> Second example