I started putting up outdoor Xmas lights (small candle shape) today, and noticed 1/2 the string, 50, probably 100 in total, were out. Nicely divided into two halves. I took the string to the h/w store to see if they knew what happened. Nope. They just refunded my money. They may have been blinking lights.
This afternoon I went out to put up a string of blinking lights, maybe
1" tall and upside down U shaped. They were all blinking. When I raised them on a pole, 50 stopped working. I counted them. What's going on? Both, I think, had 3 wires. The last set certainly did.
We still have lights from at least forty years ago. I can't remember when they were bought, I can remember the serial strings where if one bulb went bad the whole string went bad, so sometime in the sixties the non-series lights came into the house. And they've stood up well.
The small bulbs of more recent origins look nice, but yes, they are trouble (at the very least bad contacts, unlike the screw in bulbs of old) and of course, result in a semi-serial arrangement, back to "which is the bad bulb". But they are cheap, which has its advantages, but also the problems.
LED bulbs are down to what good Christmas lights used to be, they only seem expensive compared to the really cheap small throwaway strings of recent times. Buy a set of LED Christmas lights, and they'll last practically forever, just like those 1960s strings that are still running fine. But unlike the old lights, the LEDs will take forever before a light burns out, since they are LED, and unlike a lot of uses, the lights only get used for a couple of weeks each year, so the life span of the LEDs is nearly infinite.
Most now have bulbs that fail short (or some other mechanism) so that one burned out bulb doesn't make the whole string go out. A loose bulb still opens then entire (half) string, though.
1) Swap each bulb with a new bulb. Use one spare, replace first bulb, take that one and move to second, continue rotate left. Assumption #1: Only one is bad. Assumption #2: The string itself isn't bad.
2) Get a non-contact voltage probe. Electricians use these things to check for live circuits. Move it down the chain until it lights up.
Two? Both sides of the line (non-polarized plug)?
You can get the non-contact testers at the HD or Lowes for about a third of that.
I have ornaments my parents bought for me ("ooh pretty") from 50 years ago that have been used every year since. Most of the (unlit and non-tinsel) ornaments are hand-made and >30 years old. I throw out lights as soon as they start making trouble. They're too cheap (the day after Christmas) to bother with or risk.
Since we are off topic already, My father lived with his older sister as a young boy since he was an orphan at an early age. His sister gave him $5.00 to buy some Christmas lights and expected quite a bit of change in return. (1930's) She was not too happy to find out that he had spent nearly all the money on the lights. They still work today.
I bought a Light Keeper Pro at an ACE h/w store yesterday. It isolated the problem to the first four bulbs in the string that was out. My problem may now be finding four bulbs. I guess I can cut them out of the string and solder things back together.
Our local ACE store was out but selling them for $22. I happened to be on a short trip 15 miles away and found them at an ACE for $17. One of our local stores sold them at Xmas time,but was out. Not an ACE.
Interesting unit. It can solder pins down the string.
You could, but that would cause other bulbs in the remaining string of 46 to burn out prematurely. Also with a 3 wire string, you need to be able to figure out where to connect the wire (or the resistance described below to bypass the open bulbs. With some of the strings I've seen, the twisted wires make that too damn hard in my opinion.
Regarding premature burnout and resistors to replace the bulbs: Each bulb in the original string of 50 drops a certain amount of voltage. If the original string contains only bulbs and wires, then each bulb drops ~ 2.4 volts (120/50). With 4 bulbs gone, you want to find another way to drop ~9.6 (4*2.4) volts. Otherwise, the 46 bulbs are each subjected to voltage a bit higher than normal, and will burn out more quickly.
Probably easiest to buy another string, but if you want to proceed and use a resistance to drop the voltage, you'll need to measure the current drawn by a fully operational string. That will be I in the formula E = IR. Solving for R: R = E/I. E is the voltage drop, assumed to be 9.6 volts. It would be better to measure the voltage drop across 4 bulbs in the fully operational string, and use that measurement for E in the formula. R is the resistance required to drop E volts at I current. The wattage dissipated would be I^2*R and the resistor(s) would need to be rated at least twice that for a safety factor. Since the resistance might touch flammable material, you probably want a lot higher rating. More on that follows.
I don't know the specifics of your string, so I'll make up a value for I: 200 mA. Using 200 mA and 9.6 volts, the required resistance would be 9.6/.2 or 48 ohms, and the power dissipated would be 1.92 watts. I'd use 5 ten ohm, one watt resistors in series. That way the dissipation would be spread across 5 resistors which would keep the temperature lower. Whatever the actual number turn out to be, you want to spread the heat out over a large enough area to keep the temperature well within safe limits.
Replacing the bad bulbs with identical new bulbs, or replacing the string, avoids all of that.