It's that time of year again. Maybe past time, but it's really nice out today and I'm finally getting some lights up.

Over the years I've gotten quite skilled at repairing strings of those awful little incandescent bulbs. Now that prices have dropped, I'm switching to more and more LED strings. I was surprised to see a number of LEDs are out on my string that is only a few years old.

Does anyone know how these things are wired? I haven't even looked yet and would rather rely on the experience of others than reinvent the wheel for myself.

My current problem is one of those strings of twinkling icicles. In a string with maybe 30 icicles (which are 3-4 LEDs each), about 4 icicles are out. All adjacent. There are a lot of these inline bulges. Not every icicle, but maybe every 3rd.

 

The markings on the 'bulge' only refer to the heatshrink tubing covering whatever is inside. The only thing I can think is inside the bulge is a (waterproof) connection between the two wires.
A bulge every 'maybe third' icicle and 'about 4' icicles out seems very close to a coincidence. Do the missing lights tie up with the location of the bulges at all? Try wiggling/bending the adjacent bulges and see if that changes anything.

 

They may be LEDs, but you still have groups of them in series, and if any in that series group is open (bad LED or loose or backwards in socket) then the entire series group will go out. So check each one in the bad group(s) and see if you can find the culprit.

[The bulges do just look like splices, but they could also be current limiting resistors. You would need to try and 'draw out' the string wiring to make a reasonable guess as to whether they are just splices or resistors.]

 

I suspect the bulge contains a blocking diode and a resistor , plus maybe the flasher circuit, and not a wire splice. There's just way too many of them to be splices. I looked again and there's a bulge on almost every icicle string. I suppose I could start testing individual LEDs. Sigh.

 

Just some details. There are 4 conductors leaving the wall plug, which contains 2 fuses. Flashing appears to be LED-specific, since only a few of the individual LEDs flash randomly. Removing one LED took out ~4 icicles. So my problems are likely failed open LEDs as suggested by @Ylli. I don't know any way to diagnose this beyond brute force of removing each LED one by one and testing them. Groan. I thought I was free from this by going to LED.

 

Fixed 'em. The problem was corrosion of LED leads. So much for modern technology. An LED that will last forever with leads that last a couple years.

I had to find them by brute force, testing one LED at a time. I suppose using a meter might be a little faster.

 

Groan. I thought I was free from this by going to LED.

Probably a case of Computer Aided (Removal of Excess Quality) Design.
The, "on" LED in my audio amplifier burned out after only 37 years.

Anyway, thanks for the warning. A cheap light string is still cheap, even if it contains LEDs.