Repair: Types of faults

In this section we'll look at common types of faults which will help us fault find later.
Light bulb or LED failure



LHS bad alignment RHS good

Causes:

• old age, 
• overstressed due to too high a voltage / current or incorrect replacement bulbs/ LEDs used in string,
• pulling too hard on wiring and a wire/ connection breaks, 
• bad contact alignment in light fitting or a plug/ socket; 
• loose fitting of light holder into base fitting.

Result: usually go open.

Note 1: overstressed LEDs will initially reduce light output then go open.
         2: some light bulbs are fitted with a shunt - see Basics, Light bulb section for details. The shunt shorts an open bulb (ie unlit) and overstresses remaining bulbs. So replace shunted bulbs ASAP.
         3: Light string with a flasher will cause bulbs to fail more frequently and flasher will eventually fail due to old age.

Wiring in light string has a short circuit
Causes:

• in a new string: typically bad workmanship is the cause, eg a solder thorn cuts insulation to make a short circuit - see example below. The short circuit may affect 1 LED or a group of LEDs depending upon its location. It could also blow up the electronic switch in the controller.
• when hanging lights, eg a staple is inadvertently driven into a wire. 
• a stray strand of wire in termination touches the other terminal.

Result: damage occurs and may be difficult to find!

Controller fails due to component failure or short circuit in string - see above.

Water induced corrosion of contacts
The light fittings or plugs are poorly sealed due to being lowest cost products. So any lights used in the open usually suffer corrosion which may dim or prevent the lights working. It may be practicable to clean all contacts and apply a smear of Vaseline or similar to contact surfaces. This can give temporary protection.

Also transformers and controllers are not usually designed for installation in the open or where rain/ snow can be blown onto them. Consult the product manual or look at their IP rating (see Safety section).

Solder joints

Causes:

• bad workmanship as shown 
• pulling too hard on wiring causes stress on solder joint which is a low tensile joint. Also, it's best practice to stress relieve any solder joints in wiring.

Result: usually goes open

Power supply
Causes:

• Total load of lights exceeds power rating of transformer or switching power supply. 
• Poor cooling due to transformer(s) or switching power supply was/ were put into a (small) box with poor ventilation. These items are rated for open environment and when 1 or more are put into a box, the rating reduces dramatically. We'll cover cooling requirements in the Design section. 

Result:

• Transformer either burns out or internal thermal link goes open (crude protection; may reset). 
• Electronic protection operates for switching power supply - may reset then operate again.

Fuse in supply plug

Causes:

• Fuse blows due to overload (too many lights), smaller amperage fuse (than rating) was used.
• Fuse goes open due to old age or bad workmanship. I've experienced rare events of the fuse element corroding or poor welding at the end cap of a glass fuse.  This could only be detected by continuity test with a DMM.

Result: usually go open.
Note: always replace a fuse with the same type and amperage. Fuses operate on the value of current squared. So if you replace a 10A fuse with a 12A fuse, it usually gives (144/100 or 1.44) times less protection!

Solar Lights
Causes:

• poor location of solar cells, dirt or shade from tree growth reduces amount of sun recharge per day;
• internal battery ages;
• water corrosion as above

Results: lights don't work or soon go out.

Vermin damage

Cause: poor storage of items enables damage by mice, cockroaches, geckos etc. Breakage of glass bulb.
Result: throw out items and cry.

NEXT >> Fault finding methods