Help with light string

[IndianaChristmas]

I have several of the spheres shown in the picture.  After last year some of them only lit up on one side.  I took the spheres apart to see what might be wrong.
This is not a normal strand of lights, you might see that in the picture as

I checked all the light bulbs and they work.  All the lights on the lit side are lit.  I checked the voltage at the socket with the arrow pointing at it as well as the socket at the "top" of the 1/2 sphere that has the jumper to the lit side; both measure zero.

Any obvious ideas why only 1/2 the sphere lights?

[deplanche]

It might not look like a regular strand of lights, but it acts just like one of the longer strings of lights, that half will go out at a time if a bulb blows.  The wires just might not be tangled as nicely.

My guess if that if you checked all of the bulbs, there is a bad contact between one of the bulbs and the sockets.

I've used a light keeper pro to find the problem on some of the old wire frame figured that have had similar problems.

[chrisatpsu]

can only be 3 things.

bulb,
socket
loose or broken wire.