Tip & How-To about Kitchen Appliances - Others

Christmas Light Problem

Finding the Bad Bulb Ideally, the bad bulb will be dark while the rest of the string remains lit. But often that does not happen. The lights in these strings are basically in series, and any open connection, whether in a wire, at a socket, or even inside a bulb, will turn off that whole circuit. Normally the bulbs have a "shunt" which shorts the bulb when it experiences full line voltage. That leaves the bad bulb OFF, and the rest of that circuit ON, which shows which bulb to replace. Unfortunately, the shunt often fails to operate, and then an entire circuit is off. One possibility is to go down the string light-by-light and remove a bulb, test it, then put it back if it tests good. But not only is that a heck of a lot of work, it has the potential to make things much worse: When the string does not light up we cannot know that we have seated a bulb properly. These strings generally have sockets that work well enough as long as we leave the bulbs in the socket. But when we put a bulb in, we may have to try several times before the socket makes contact. Only when the string lights up do we know we have been successful in seating a bulb. So if we are working on a dark string, we might find the bad bulb, and yet have the string still not light because several of the bulbs we re-seated are not making good contact.

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how to fix Christmas lights


Just replace the bad bulb. Finding the bad bulb is a different matter if it is a series string. They sell testers for a few bucks, with a little practice they work good.

Dec 18, 2014 | Christmas Lights Etc Toys

1 Answer

Christmas light string was half lit. Mid way between the unlit section we found a loose bulb. We replaced it, but now half the string blinks and the other half remains lit. Help!


There could possibly be a short in the wiring. Have you checked for any exposed wires or holes in the plastic covering? Moisture could have gotten in there and shorted something out

Nov 25, 2012 | Home

1 Answer

how wiring diagram for christmas lights work


All the bulbs in a section of lights are connected in series, meaning one after the other, like links in a chain. If one bulb goes out the chain is broken and that section goes out. All modern light sets have bulbs which have a built-in feature called a shunt. The shunt in the bulb is supposed to short out if the bulb filament burns out. The advertising wording would be something like 'if one bulb burns out, the others stay lit'. It usually works, but there are limits. Sometimes the shunt in the burned-out bulb fails to work and the chain remains broken. You have to find the bad bulb and replace it. Also, every time a bulb burns out, if the shunt is working and the other bulbs stay on, the power to each remaining lit bulb increases. This puts a strain on the remaining bulbs, which is why you should always replace burned out bulbs as soon as you discover them. If you don't and more bulbs in the same section burn out, you can reach a point where there's too much power for the remaining bulbs to handle, and all (or at least many) of the remaining bulbs will burn out, necessitating a replacement of the string.

Dec 15, 2011 | Christmas Lights Etc Santa's Toy Truck

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