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...
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
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 :)
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
Take it easy. Merry Christmas, or whatever.
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.
(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.)
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.
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
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.
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 http://notstupid.us/graphics/xmas2009.mp4 (although
be prepared for a 6MB download).
On Tue, 22 Dec 2009 10:42:51 -0500, "Ralph Mowery"
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
At least take a look at the videos at http://lightkeeperpro.com . 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
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.
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