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It's that time of year again... Christmas tree lights

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NivagSwerdna:
So... dusted off the old Christmas Tree lights (incandescent strings), tested them, put them on the tree and then 24hrs later a segment doesn't work... so...

Although the incandescent technology won't be us beyond the last spare bulb (we have a few) it got me to wondering again how I could go about working out the broken bulb...  it seems that the wiring goes from the 240V plug to a set of parallel strings and that a single failure in one of the strings leads to the string going out.  I have read about gadgets that help diagnose but I don't know how they work.

I was wondering... maybe I could unplug the set from the mains and inject a signal into both sides of the string... say square wave on one side and an exactly out of phase signal into the other side.  Then I could measure the amplitude at the two pins of the light bulb which will give me two voltages for each of the phases... four measurements in total.

Does that sound enough to identify which direction the fault lies?  (I have to factor in the flow in the reverse direction around the correctly functioning strings)

rvalente:
Usually to fix the lights all you need is some patience, spare bulbs and a meter in continuity mode.

 I do not believe the segment is bigger them 15 lamps in series. So you could check eye naked for broken filaments.

As for testing in a fancier way, maybe using a waveform gen and a probe, you could try to find the electric field in the string. Just a thought

richnormand:
I use a AC voltage detector as sold in many home improvement stores. These are cheap and will beep when an outlet is live.

Separate, by hand, the wires between the live and the neutral.  Check to find out which is the live at the plug.
Follow it to the first bulb, then keep separating the wires and tracing until the signal dies down. The open bulb will be close.

This also works with LEDs as I found out this year (open blue LED in an old string).

james_s:
I use either a multimeter or I just get a known good bulb and swap it into one location at a time. Most of the time with the push-in miniature lamps it's not the bulb that has failed but one of the wire leads has broken or is bent around and not touching the contact. The type we've had here at least as far back as the early 70s has shunts in each lamp that prevent a burned out filament from opening the circuit.

While I've been LED everywhere else for years I'm not fond of LED christmas lights. They flicker, most of them are dim, they all have exactly the same colors immediately identifiable as LED, there's just something I find icky about them. I'm using 1970s C9 lights on the outside of my house and my tree has a mix of C6 strings from the 40s-50s and some 90s C7 bubble lights, all of it incandescent.

GreyWoolfe:

--- Quote from: james_s on December 20, 2019, 03:56:09 am ---I use either a multimeter or I just get a known good bulb and swap it into one location at a time. Most of the time with the push-in miniature lamps it's not the bulb that has failed but one of the wire leads has broken or is bent around and not touching the contact. The type we've had here at least as far back as the early 70s has shunts in each lamp that prevent a burned out filament from opening the circuit.

While I've been LED everywhere else for years I'm not fond of LED christmas lights. They flicker, most of them are dim, they all have exactly the same colors immediately identifiable as LED, there's just something I find icky about them. I'm using 1970s C9 lights on the outside of my house and my tree has a mix of C6 strings from the 40s-50s and some 90s C7 bubble lights, all of it incandescent.

--- End quote ---

We have just the opposite experience.  We have gotten rid of all of the incandescent lights.  We have lights on the tree that are very bright, garland hung around that are somewhat dim, which is perfect and some fairy lights on shelving units and all have a different shade of white.  The outside icicle lights are also quite bright along with the lights on the outside tree.  The LED lights on the reindeer are not as bright but still very noticeable from several houses away.  None of us notice any flicker at all.  I much prefer the LED lights.  I do miss the bubble lights of the 60's on the tree that I grew up with, though.

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