Good evening to all, and may all your lights work. I encountered the age-old problem of half the strand not working. I discovered it before I put it up on the eaves. This year, I got an early start on my lightscape so I had time to troubleguess the offending strand. I inspected the wire for breaks. Then, I plugged it in to the wall socket. I removed one LED at a time, starting at the plug end. After the sixth LED, I was ready to quit. LED #7 proved to be the problem. The prongs of the LED were misaligned in the base, so they couldn't make contact with the socket. I pushed the prongs into position, put the LED in the socket, and the rest of the strand came to life. The whole task took 10 minutes. The best part is that I was able to live up to the expectation of my 7-year-old granddaughter who was observing the process. In her words, "Good job Granpa." I hope this answer is helpful to someone. Happy Holidays, from Phil in Kansas.
"This business of flipping the plug, using oscilloscopes, or noting hz is all indicative of not understanding Diodes. LED's (Light Emitting Diodes) only work with the current flowing through them in one direction... direct current. Alternating Current (your house current) fluctuates or oscillates 60 times a second.. hence ""60 hz"". In order for your LEDs to wok on that circuit they need half of those oscillations to be eliminated. They also need the voltage to be greatly reduced.... from 110 down to about 5. LED's also cannot be tested like an incandescent string of lights using an ohmmeter because they have no filament. Testing a bring of LED's would require setting up your multimeter as an ammeter, breaking and testing the light string only (not the other two lines.
Because the string is made to work AS A WHOLE UNIT with AC power, the observation that flipping the plug should alert you that this function has been destroyed. The fuse was there to prevent further damage (fires). The fact that you can replace them should also bring with it the caution that you need to find out what caused the failure in the first place.
A shorted bulb in one of your strings most likely caused a failure in a diode that changes that 110v AC to DC . That event likely caused the fuse to blow. Replacing the fuse or flipping the plug does not address the root problem, and my bet is that you will have to toss the string and buy new.
While you are inspecting your defunct string, break into and have a look at an LED. See that the two electrodes inside are different sizes. The large one is the negative side, the small is the positive. There is space in between... no filament. The polarization of the two poles, and not current flow from one to the otheris what makes that space in between give off light. In fact, if the voltage is too high (AC or DC) that space will be violated and the LED will literally ""pop its top"". Depending on the element in that matrix, you get different colours. Red is the cheapest light to produce. Clear light is one of the most expensive."
Same problem, new solution. I tried new fuses and still the one end of each string would not light up. So I thought...Since one string has the plug end that won't light and the other has the receptical end that won't light, what if I cut the strings and put the two ends that do work together? Making sure that I connected the one wire that runs straight thru the entire string to the same on the other side and the other wire that goes into the bulbs together I now have a complete string of working lights. Forgive me but...I somehow feel like a genius right now :). And a special thank you goes out to my daddy, who passed away on Christmas Eve in 1981, for letting me tinker in the garage with him when I was a child. And to all a good nighttttttttttt!
"Yes, LED christmas light strands are often two independent circuits.
The LEDs are connected in series, so if one is disconnected or somehow failed open circuit, that circuit will go out. Of course the same will happen if there is a break somewhere in the wire.
You could check with a voltmeter to see if you are getting 120vAC out of the socket on the tail end, which if zero would mean a wiring break.
But I think chances are you have one failed LED.
Further testing would mean cutting into the strand."
"The small catch in you plug is where the fuses are. You should find two of them in there. I am not sure where you are located but I get my replacement fuses at Walmart and its a lot cheaper and less time consuming to start with that. Give it a try and thanks for the Christmas Spirit....Good luck.
UPDATE
just added an image due to another question about this...."
