Sort of OT- string of 2.5 volt bulbs that won't light for Christmas

[Dave]

Bottom line, I've got a string of lights that tests good in all ways, but won't come on. (They worked fine last year...) There is voltage all the way to the end of the string, at the plug that goes to the next string. Just no lights lighting. Have already replaced a couple dozen of the 2.5 volt bulbs, and troubleshot it in every way I can think of. The fuses are good, and ohming out the entire string by plugging my meter into the far end and shorting the prongs with a paper clip gives me a reading of 1.1 ohms. Am guessing the the coiled nature of the bulb elements is what keeps the AC from throwing a breaker. I am an electronics technician, so feel that a string of holiday lights ought to be simple. Only it doesn't seem so. What gives? Any ideas? All ears...

Many thanks,

Best,

Dave

[Zootal]

There is a burned out bulb somewhere or a bad connection in a socket, causing the circuit lighting the bulbs to open, so no bulbs light. There is a third wire that passes the current to the end of the strand so that other strands plugged into it keep burning when the bulbs burn out.

The 1.1 ohms you read is not the circuit with the lights on it, it's cumulative resistance through the wire and maybe resistance at the connection of the paper clip. You can't test the lights that way.

To test them with a meter, remove the paper clip and put your meter across the two prongs that go into the outlet. If it is open, then your light strand is open somewhere. It's that simple. You can't measure resistance from one strand to the end because that circuit bypasses the bulbs themselves.

I have learned from cold hard experience that once you start playing musical bulbs with these things that you are better off throwing it in the trash and replacing it. Xmas lights are of such piss poor quality that you no sooner find the burned out bulb and go to hang the lights, but another bulb burns or opens and they lights go off again. All you have to do is bump it on something and it's dead again. Throw it in the trash and go buy another set of lights :)

[Dave]

Hmm. Yeah. Rats. Well, thanks for the input and feedback. :) I guess I was just hoping to be able to use the string that fit the application so perfectly. Oh well.

Again, many thanks. Truth isn't always what you want it to be, and all that...

Take it easy. Merry Christmas, or whatever.

Dave

[Art Todesco]

You really can't test using an ohmmeter. Many times problems like this are caused by bad connection in the socket (corrosion) or a bulb that is burned out and the internal shunt didn't short out. A number of years ago I build a test box that has a 120 to

240 volt autotransformer in it. If you put this directly to the lamps it would surely kill the entire string. However, I put a 1/2 wave rectifier and some resistors in series. The higher voltage helps to burn the shunt in a lamp where the filament is open. I also have a test lead on the box where you can probe individual sockets. Since that time there has been a great product on the market called Light Keeper. This unit put a high voltage spike into the string to help burn through the shunt in a bad lamp. I still use my test box for problems that the Light Keeper doesn't fix, however, those cases are much fewer now.

[N8N]

True dat. If you INISIST on troubleshooting it, step one is to find a string of lights that works, then remove one bulb, and take every single bulb from the dead string and test it. It's the only way.

nate

(was the official xmas tree light bulb tester as a kid. Now that I think about it, methodical troubleshooting is a skill that I use regularly in my Real Job(tm) even today. So there's that.)

[Jon Danniken]

And put on an album you like to listen to, makes the tedium go by more enjoyably.

Jon

[Ralph Mowery]

What keeps the low resistance of the bulbs from triping the breaker in the house is that as the filiment of the bulb heats up, the resistance goes way up. The coiled nature of the bulb elements has almost nothing to do with it. I would have thought an electronics technician would know this.

While it does not always work one thing that sometimes helps is to get one of the 'hot sticks' That is a device about 5 inches long and 3/4 inch in diameter. When you hold it close to a wire that has power in it, the tip of the stick glows. You plug in the string of lights and run the stick along the wire and when it stops glowing you are near the break in the wiring or bad bulb.

[Pavel314]

I remember trying to find the bad bulb in a string of those old fashioned pointy bulbs as a kid about 50 years ago.I didn't realize that they still made strings of Christmas lights like that, when one goes out, they all go out.

Paul

[hrhofmann]

All of the so-called Italian lights are series strings, only instead of 8 bulbs in series, they put anywhere from 25 to 50 bulbs in series

[Mark Lloyd]

I've fixed some light strings that way. You have to separate the wires enough that the tester doesn't pick up voltage from another wire.

Some strings just give inconsistent results, and need to be thrown away.

[Nate Nagel]

It's the only way to make them blink in unison. otherwise you'd have to use a flasher bulb in every position, and then they'd twinkle, not blink.

nate

[mcp6453]

At least take a look at the videos at

I bought one of these for myself this year and gave one to a friend. It's the easiest way to keep light strings going, particularly on a pre-lit tree. They're probably on clearance this time of year.

Christmas bulbs are more complicated that you would think. The shunts that keep the rest of the string burning when the bulb burns out don't activate half the time.

It sounds like you have a bad contact in the socket of one of the bulbs. Also, since the bulbs are in series, it is possible to have a string with every bulb bad. If you replace 1/4 of the bulbs and plug the string in, you will instantly blow every bulb. Been there done that.

I have no connection with Light Keeper Pro, but I am a satisfied customer. Even if you don't buy their tool, their free videos are very helpful in understanding Christmas tree lights.

[Mark Lloyd]

[snip]

I have over 3500 bulbs all blinking in unison (and another 3000 or so blinking EXACTLY out of phase). They're in about 180 series, not the one you claim.

There's a video at

(although be prepared for a 6MB download).