A D'Lighted Blog
As decorators move into the LED world, sometimes repairing them are nearly impossible.
Tim Fisher of Plymouth Lights shared an article about repairing LED's. Here's his technique... I'm making available the technique that Ive had some success with in diagnosing LED's. Note that so far I have only used this technique with SEALED LED's (that is, ones which don't have removable bulbs). I'm assuming it would also work with removable LED's, but have no experience with it.
To use this technique, you will first need to create a simple tool. To create this tool, you need two plastic push pins, of this style here. You also need a length of wire, about 3 feet is pretty good. Strip the ends of the wire, wrap each end around the metal part of the push pin, and solder it. Take your multimeter (you have one, right? if not, maybe this tutorial isn't for you), put it in continuity check mode, and verify that touching a lead to each push pin point gives you continuity. Now onto the technique. For the sake of this discussion, when I say "bulb" please realize I mean LED. Old habits die hard:
When an LED dies, it's sort of like a mini-light in that it breaks the series so the whole section goes out. So the trick is to find the bad 'bulb', or LED. You could try using a Lightkeeper Pro for this. I've heard some say they've had good luck with this, but I can't get it to work with any of the LED's I own, hence this much more complicated technique.In the following steps, I refer to the SERIES wire. This is the wire that will visit every bulb in the section. There are typically two other wires that go along the string but don't visit most bulbs. In fact with the Diogen-style sealed strings, they don't visit ANY bulbs but just the blobs along the string. Make sure you're ONLY piercing the series wire, not the other two.
1) First, push the pin through the series wire right before the first bulb in the dead section (if your lights are like mine, this will be between a "blob" and the bulb, and will be the center wire going into the blob). Make sure it goes through the conducting part of the wire and not just glances the insulation. Pierce this one all the way through so the push pin stays connected to the wire when you let go.
2) Now, jump forward 8 bulbs or so and quickly pierce between two bulbs on the series wire. One of two things will happen:
a) Nothing. That means the 'bad' bulb is not in that group of 8. Count off 8 more bulbs and try again.
b) The rest of the string (beyond your ' jumper' lights up). Congrats! You've narrowed it down to 8 bulbs. What I then do is back up one by one. If you back up and the rest of the string still lights, that's not the bad one. If you back up one bulb and nothing lights, that should be your bad bulb. You can confirm this by unplugging both tacks, and piercing the series wire on either side of the 'bad' LED. The whole section should light up minus that bulb.
3) Now you've found the bad diode. If you use sealed led's, you'll need to cut it off. Then go to your stash of dead LED strings that you probably have and cut off a diode from that one. Strip the wires and temporarily twist together (power off!). Then connect power. If everything works (including the new LED) you're good to go - use heat-shrink and solder to make it permanent. If not, reverse the 'new' diode and try again, that should work.
Couple hints on Step 2:
- Note that by bypassing groups of LED's, you're overdriving all the rest of them. So you want to do the tests very quickly to minimize stress on the good diodes.
- To further minimize stress on the diodes, one you get about halfway through the string (if you haven't found the bad section yet), remove the first pin from the start of the bad section and move it to after the last bulb in the bad section (if your lights are like mine, this will be between the last bulb and another 'blob'). That way you're never overdriving more than half the string with twice the voltage.
A few further disclaimers:- Make sure that your push-pin ONLY pierces the series wire. This is the wire that "visits" every bulb in the section. There are likely two other wires that, if your LED's are like mine, don't connect to ANY bulb in the section, but only to the rectifier blobs. These bulbs carry 120VAC power and if you 'jumper' one of these to the series string, you might just blow something up. If you jumper them to each other, you might just see small fireworks and blow the circuit breaker :)
- Use plastic push pins for your tool, and don't touch either metal point when power is connected!
DISCLAIMER: This write up is for educational use only. If you follow these steps, you do so at your own risks. Please read the ENTIRE write-up before following ANY instructions, most importantly the "additional tips" and "disclaimers" toward the bottom. If you end up destroying your LED's further, burning down your house, getting a shock, killing yourself, etc. etc. I cannot be held liable, even if these steps are grossly wrong, incomplete, or dangerous. Got it? Good. ***Finally*** please do not PM me with support questions about these steps. Feel free to post questions about them in the LOR-Users group and even tag me in the comments, but I don't have time to answer every PM that will certainly result from people trying, misunderstanding, not reading, etc.
This article cannot be republished without permission from Plymouth Lights.