How can I fix my prelit xmas tree with one section that isn't lighting up?

These things are such a pain. The bulbs are designed to still conduct even when burned out - so more often than not the problem is a loose, missing, or broken bulb. Look really closely at each bulb and push each one in extra good.

No luck? O.K. you need a bulb tester, but you don't have one. However you do have other sections that do work. Take all bulbs out of the dead section and put them in a bowl. Swap one bulb from the bowl with a bulb from a working section. Does the bulb work? If yes, put the one you just pulled out into a socket of the dead section and test the next bulb. If no, throw it away and try another. Pretty soon you've filled most of the dead section with known good bulbs and thrown away one or two bad ones. Now finish the dead section with new bulbs and say a little Christmas prayer.

If you have a bunch of burned out bulbs in one circuit the set will get to the point where every other bulb will almost instantly burn out.

This is because as each bulb burns out, there is a shunt in the bottom of the bulb with a non-conductive coating on it, but when the bulb burns out, all of the voltage in the whole circuit piles up at this shunt and burns off the non-conductive coating, allowing current to bypass the burned out bulb.

This shunt doesn't provide as much resistance as a bulb, and what happens is that instead of say 120 volts over 20 bulbs, you will have 120 volts over 15 bulbs if 5 are burned out. So instead of 6 volts per bulb, you now have 8 volts per bulb.

This will greatly increase the electricity to each bulb causing it to burn way brighter than design and lower it's life. Eventually the voltage to the remaining lights gets so high they just ping right down the line and every bulb on the whole string is burned out.

Moral of the story, it's important to change out burned out mini lights to avoid burning out the whole string.

I should mention, if you have a section of a string where every bulb looks black (burned out) the only way to light that section is to change out every bulb with the power off to the string. You'd obviously not do this with a cheap string, only an expensive one, and the cheapest approach would be to buy a cheap string with the same number of bulbs per section, and use them as replacements. Just make sure the bulb voltage is the same on the original string and the one you are using as a replacement.

You may have a loose bulb. If not, take a new bulb and change it along the line and hope you can find the bad one. Maybe broken. I had a string like that. Takes time but, I found it. Good luck.

first its christmas next get a bulb you know works move from socket to socket till the section lights up. be careful those little wires from the bulb are delicate and if they are off just a bit or broken NO LIGHT

wow that seems to be my yearly problem .. changing bulbs, tracking cable with multimeter in the end now i dont bother .. just buy new ones .. maybe im luckier than you the are cheap where i am

Ma dads plugged 5 sets of lights in just now,but al guarantee he gets more

something is not making the connection. Chuck out the broken bit and buy a new piece