A bit of a low-tech, although seasonal, question for you:

I have a bunch of Noma LED Christmas light strings, each with 70 LEDs. With one string, exactly half of the LEDs don't light up when plugged into the AC. The whole string used to work, and it's only about a year or two old.

My understanding is that Christmas light strings like these are often two independent circuits, with fuses built into the plugs at either end. I notice that most of the way through the string there are three wires—but at the middle-point of the string, there are only two wires joining the 2 halves. So, this idea that there are actually two independent circuits seems to make sense to me. There must be a fault in the 2nd half of the string, or the fuse in that half must have blown.

My question is this:

Has anybody ever tried repairing this kind of LED Christmas light string? Is it worth it to try replacing the fuse? (Of course, it would only make sense doing so if there wasn't some other more serious fault in the circuit—but how would you debug the cause of the failure?)

The plug at the end with the problem looks like it has a small catch you could push in with a small screwdriver, but it appears almost impossible to pry open the plug without damaging it. Even if I did get the plug open and find the fuse, I'm wondering if the fuse is even some standard size or type that can be readily replaced. Is this just a one-shot type of fuse?

Failing repairing the 2nd half, I might cut the string in two and just insulate and seal the cut end with heat shrink. Has anybody done this to a broken string of LED lights?