[twinboston]

Looking for some advice on troubleshooting a small pre-lit Christmas tree.

Tree Specs
3 segments, 150 lights with (assuming) 50 lights per segment
Top segment has only a male plug, middle and bottom have male and female
Bulbs are 2.5V, .425w
Each segment is wired in some type of parallel configuration

I assembled the tree as normal, and it was completely dead. I plugged in each segment momentarily, and all three were dead. I noticed that on the top segment, there were a number of bulbs burnt out (noticeable black residue on the bulb). I purchased two new sets of lights that met the same specifications for voltage and wattage, and replaced all the bulbs on that segment including the fuse bulb (was not soldered), using the existing bulb bases and the new donor bulbs. This fixed the top segment.

I did the same thing with the middle segment, but it was still dead. I checked the fuses by swapping the fuses from the top segment, still dead. I swapped the fuses back, and plugged the top segment into the middle section, and it illuminated, so I am getting voltage through the whole string. I double checked to make sure all the bulbs were seated correctly.

I have a BulbKeeper Pro, so I plugged a socket in and tried the shunt repair, which also did not work. Before I start tracing down broken wires or sockets, I'd like to clear up how exactly this tree is configured, as I've never run across this wiring configuration before.

The attached photo shows the first socket after the male plug:

A: Originates from the small "wing" off to the side of the bulb, continues on through the bulb series, but does not connect to any sockets
B: Originates at this socket, connects to next socket in line
C: Originates at the male plug
D: Originates at the male plug, connects to the last socket in the series, which mirrors this socket, except it does not have a fuse bulb
E: Originates at this socket, connects to female plug

My two questions are:

1. What type of wiring setup is this? Some type of dual-parallel?
2. Given what I have replaced/tested already, am I down to testing wires/sockets?

 

[dmxtothemax]

The picture shows a series configuration
Not a parrallel configuration.
Most light sets of that size use a
Combination of parrallel and series arrangements.

 

[twinboston]

The picture shows a series configuration
Not a parrallel configuration.
Most light sets of that size use a
Combination of parrallel and series arrangements.

Two things:

1. This almost has to be some type of parallel configuration, as I can remove a bulb from the working segment, and it stays lit. Just confirming, this is physically removing the bulb, not having a bulb burnt out and using the shunt.
2. I know that in a series configuration, one wire would connect from the plug directly into the socket (C), and one wire would lead on to the next socket in series (B). I also know that there would be a wire spliced in that would power the female receptacle (E). In that case, what do wires A and D do?

 

[dmxtothemax]

I would guess that the three segments
Are wired in a parrallel arrangement
Does each segment work indepently ?
As for the middle segment passing power
This could be because of a parrallel feed
Or because of the shunts in operation.

You may have to test each lamp
and make sure each lamp doesn't just
Pass current but actually lighs up.

 

[twinboston]

Well, the age-old adage is true: appearances aren't always what they seem. Wire "A" wasn't a wire; it was just some string-like fibers with the same coating as the stranded copper wires. What on Earth it was there for, I have no idea. It was throwing me because it didn't show any current when I was testing the start of the strand, and I was trying to figure out if it was supposed to be a neutral or if it was a broken positive.

Once that was out of the way, things made more sense. I was able to trace it down to a bad socket, which was easily fixed with a donor from the lights I scavenged the bulbs from.

 

[AllanJ]

I have never seen a "mini-light" string (bulbs about 1/4" in diameter) where all except perhaps one or two scattered bulbs are on and you remove one of the lit bulbs and all the bulbs that were lit stay lit.

But you can have a series-parallel string, let's say they are arranged:
A-B-C-D-E-F-G-H
and you remove bulb B and bulbs A, C, E, G stay lit.
If bulbs D, F, H were not on at the moment on then removing B might not cause anything else to happen.

Think of zones, where A, C, E, G are on one (series) zone and B, D, F, H are on another zone. Like furnace heating zones.

There do exist series light systems where the shunt is in the socket and remakes the circuit if a bulb is removed. This is a significant added expense and electromechanical complexity so I would not expect to find it in a string of Christmas lights.

In your picture , looks like you are holding the socket just before the female connector.

D is the home run from the female connector back to the power source, except for a stop at the first socket after the male plug where it is bonded to the actual hot line from the male plug.
C is the "neutral"
B is the series circuit for the sockets in this string.
E is bonded to C to continue the neutral over to the female connector.
I suppose A is a "suppport cord" to reduce stretching strain on the other lines.

 

[AllanJ]

In your picture , looks like you are holding the socket just before the female connector.

D is the home run from the female connector back to the power source, except for a stop at the first socket there to start the series circuit for the sockets in this string.
C is the "neutral"
B is the series circuit for the sockets in this string.
E is bonded to C to continue the neutral over to the female connector.
I suppose A is a "suppport cord" to reduce stretching strain on the other lines.

Exceeded the 30 minue elimit for editing so more corrections are here.