Repair Christmas Lights

7,692

54

23

About: I am an author and a maker. My current project is Santa's Shop. I'm working on a science fiction type book--more later. @EngineerRigsby

Your string of lights has a large "dead" section AND you can't find the replacement bulbs AND you don't know the location of the fault--but you hate to trash the entire string. You can probably fix them without too much hassle!

Step 1:

I have bags of replacement bulbs scattered through my garage, but the creativity of the light producers results in light sockets of many shapes and sizes, none an exact fit to the string under repair.

Step 2: Repairing an Individual Light

Fixing an individual light is easy. Let's assume the green socketed lamp on the left is bad.

Step 3:

Bend the wires down from the bad lamp (green socket) and good lamp (red tip).

Step 4:

Pull the glass lamps straight out.

Step 5:

Place the good lamp (red tip) into the green socket.

Step 6:

Bend the legs. You now have a working light that will fit your defective string.

Step 7: Finding the Bad Spot

If the bad string of lights is embedded in a tree, you might consider a light repair tool (I can't personally vouch for this--reviews are fairly positive).

These light strings are generally "groups of 50 in series." Each group represents about 120 ohms.

Step 8:

Use an ohm meter with pointed probes (multimeter on ohm setting).

Step 9:

Mark the start and end of the "dead" section using masking tape.

Step 10:

You will start with 50 dead lights. Unplug the lights. Go to the center of the bad area and remove one light (I use a tiny flat blade screwdriver to pry the bulb assembly from the socket). Press one probe (we'll call it probe A) against the right side of the lamp socket. Press the other probe (probe B) against one of the flat blades of the plug. If there is no reading, move probe B to the other blade of the plug. If there is no reading, the problem is to the right. Do the same process to the left. You should find continuity on one side of the lamp socket and no continuity on the other. Move the masking tape marker to this point, pointing toward the bad area. You have narrowed the problem to twenty-five bulbs.

Repeat this process and you will be down to twelve.

Repeat again and you are down to six; followed by three.

Step 11:

In theory, each bulb has a shunt, so filament failure should not cause a blackout.

Shunts sometimes fail. Filaments often burn out.

I have also seen (many times) a situation where the bulb (on the test bench) is good and the socket is good, but together they don't work. If the little wires on the bulb are very tight against the bulb, they may not make contact with the socket. Pull the wires out (like the second photo), insert the bulb and all should be well.

Have a brilliant holiday season!

Make it Glow Contest 2018

This is an entry in the
Make it Glow Contest 2018

Share

    Recommendations

    • Big and Small Contest

      Big and Small Contest
    • Holiday Decor

      Holiday Decor
    • Toys Contest

      Toys Contest

    23 Discussions

    0
    None
    SeanM364

    3 days ago on Step 6

    My favorite part of the holiday season! Some thoughts to add - that red tip bulb typically is a blinker bulb. It's filament heats up and curls back to break contact. It then cools to make contact again - thus, the blinker.

    The light repair tool you reference is worth it for the Maker types. It addresses the shunts that don't do their job as you describe. You to place an empty socket on it and pull a trigger. It is simply clicks a piezo (like the lighter on a gas grill) that sends a high voltage on the line. Any of those shunts that didn't work correctly you mentioned will be forced to close. In turn, the strand will be restored and single bulbs that are blow will be out. This will save you considerable troubleshooting time.

    Happy Holidays!
    Sean

    1 reply
    0
    None
    FlyboyronSeanM364

    Reply 2 days ago

    Lightkeeper Pro. First "As seen on TV" thing I've ever decided I can't live without.

    It actually does work! Most of the time.

    Especially if you don't wait until so many bulbs are out on a string that it overloads the rest and blows the all out.

    3
    None
    mewoodwork

    3 days ago on Step 11

    I teach electricity in school and this is the first time I have seen a schematic of the wiring of the light string. I have tried, but always gave up! This is great and I will never have to throw a string out again, filling a spot in the land fill. Thank you and great job.

    7 replies
    0
    None
    kermykiemewoodwork

    Reply 3 days ago

    With due respect, your comment about teaching electricity but not having seen a basic schematic of a series circuit gives me great concern. Series and parallel are something a teacher should know without needing a schematic.

    1
    None
    mewoodworkkermykie

    Reply 2 days ago

    I normally do not reply to "instructables" because of people such as yourself. I never mentioned not knowing series and parallel circuits. My comment "I teach electricity in school and this is the first time I have seen a schematic of the wiring of the light string. I have tried, but always gave up! This is great and I will never have to throw a string out again, filling a spot in the land fill. Thank you and great job." This is the first time I saw a schematic of the Christmas Tree Light circuit that was presented as clear as the one sketched. The light string is one of the many projects of reverse engineering that I have my 8th grade electronics students perform. Public education is still the only education system that helps students learn to work and get along with others. You sir, jump to conclusions you believe to be true and are not. Your "great concern" is not warrented. I apologize for this reply, but I am very proud of my students and my ability as an instructor.

    1
    None
    kermykiemewoodwork

    Reply 2 days ago

    Sincere apologies for any offence to you, my concern was directed generally at the education system in the UK which I have worked in. I now run an electrical engineering company. Sadly ed' here is filled with apathy, lack of control, increasing violence. So apologies to you personally and I do not want to get political and keep to the instructable which was good and informative.

    0
    None
    mewoodworkkermykie

    Reply 2 days ago

    Thank you for your reply and I accept your apology. Educating the young is very important to me and I agree with you, this site has to remain open with information and ability to share ideas with others.

    0
    None
    Flyboyronkermykie

    Reply 3 days ago

    With all due respect, this is a fairly complex combination of serial and parallel circuits that's much easier to understand when laid out this way.
    In my own case, I'm usually working on a pre-lit tree with about a dozen strings containing well over 1200 lights, so the actual wiring circuit is very difficult to trace in place on the tree.
    I appreciate the schematic, as I too have never known exactly how the multi-section circuit was wired.
    Thanks for the diagram!

    1
    None
    kermykieFlyboyron

    Reply 2 days ago

    Out of interest sir, a tool I find indispensable in my box is the RF cable tracker commonly used by telecom engineers. A quick way to localise the fault without even removing bulbs or invading insulation. Seasons greetings to all.

    0
    None
    kermykieFlyboyron

    Reply 2 days ago

    Fair comment sir, it may be that I have seen it before and it is usually the 3rd wire that catches people out. However my comment was about "teachers" these days. My own son is in his final year of school and I find that what they do not learn these days or what their teachers can not answer from pupils leaves the education system lacking. The instructable itself is very informative and useful, a great clear guide to many people of all skill levels.

    0
    None
    Thunderone2

    3 days ago

    Another problem that you will find with either the incandescent or LED bulb/sockets is that they will rust in the outdoor strings. Sometimes a simple swipe with fine sandpaper will produce a good contact. When I replace/repair any strings I place a coating of vaseline on the bulb wire ends, (very light coating). Seems to make the string last longer. This is a trick I used on the older incandescent bulbs so they can be removed without breaking the bulb during removal. Eliminates or reduces oxidation. I'm also a electrial engineer and really hate the process of fixing any sections of inoperative strings.
    Good instructable!!!!

    1 reply
    0
    None
    FlyboyronThunderone2

    Reply 3 days ago

    All the strings I've seen use copper or brass contacts. The DO sometimes corrode, but unless yours are steel, they won't rust.
    Using Vaseline is fine and it does help. There is also a product called "Bulb Grease" which is likely Silicone, that does the same thing and stays put longer in my experience than Vaseline in an outdoor setting.

    0
    None
    Flyboyron

    Tip 3 days ago on Step 2

    Keep in mind that the red tip bulbs are usually flashers, not standard bulbs. The do indeed work, but they will make that section flash on and off.
    I get my spares for these repairs from old sets of similar lights.
    When they're not worth fixing anymore, I strip out the bulbs and keep the working ones.
    As long as the voltage is the same (90% of 50 to 200 light strings are 2.5 Volts)
    you can replace them when you find the bad bulbs in your set.

    0
    None
    MikeD11Shawn Harper

    Reply 3 days ago

    No! LED'd are semiconductors, like a diode, and only conduct in one direction. Much harder to fix. You can take your volt meter and set it on the diode setting and get each individual LED to dimly light but all my LED strings don't have removable lights. Luckly these LED's don't fail until the rabbit eats the wire, ARGH! I did fix that string but I'm an electronic engineer and it wasn't easy!

    0
    None
    TCSC47Shawn Harper

    Reply 3 days ago

    I haven't tried it but I don't think it would work for LEDs. If you have your meter one way round you may have reverse bias of the LEDs and so no reading on your meter. The other way round and you will be forward biased but there will need to be 1 to 1.5 V across each diode before they conduct and your meter may not supply this voltage in its ohms test mode. So again you will get no reading on your meter.

    The other problem with LEDs is that they are all soldered in so you would have to cut the insulation to get at the wire, and it is going to get a bit messy, I would think.

    But of course the advantage of diodes is that they don't suffer anywhere as badly as filament bulbs and their unreliable sockets. I have just hung up my LED lights I bought 10 years ago and they are still working perfectly. Back in the day, I could get out of all the other Christmas chores trying to get the blessed tree lights working!

    1
    None
    sbelectrics

    3 days ago

    You should probably mention that the individual lamps come in a range of voltages, from as low as 1.2V up to about 12V, and must match the one you are replacing, give-or-take about 10%, or it will be very dim or blow almost immediately.

    1 reply
    0
    None
    TCSC47sbelectrics

    Reply 3 days ago

    Totally agree. Easy to check if you have an ohm meter. Measure the resitance of a bulb known to be working and check that the replacement bulb has the same resistance. My problem with this was getting a decent contact between my probes and the wire of the bulbs. Very fiddly.

    1
    None
    TCSC47

    3 days ago

    Good one. Many people think electrics and electronics are difficult, but a lot of problems are solved with the logical thinking shown here.

    I would add that if anybody asks why do we need something like this with the very reliable LED lights we have nowadays, I would counter that filament bulbs tend to have a gentler and softer illumination that many people prefer.

    0
    None
    ChrisB294

    3 days ago

    Very helpful. Thanks. I have so many faulty strings from over the years that I have not had the heart to throw out. Now, I can get to work.