Christmas tree light question

You have encountered the dreaded fuse-bulb. It is a bulb without the auto-shorting device the normal bulbs have to keep the string lit so that if too many bulbs fail and short, it will blow instead of the string overheating and the string isn't a hazard. In the old days before the lawyers got in on the act the fuse-bulb used to be replaceable. Unfortunately a few idiots put a 'normal' bulb in there and sued and you are now stuck with the result. The manufacturers understandably made it tamper-proof rather than just changing the socket to prevent 'normal' bulbs being fitted. I put '' round normal because a normal bulb for anything EXCEPT series lighting strings is the SAME as a fuse bulb and DOES NOT have the shorting device.

If you are experienced enough to replace it safely, all you need is a miniature bulb of exactly the same current rating as the string without a shorting link and a suitable holder with adequate insulation for mains use. You said you have gone LED for everything else. If you still have any old strings, you will probably be able to rob something suitable from one of them. If you lack the skills, parts and tools required then PLEASE forget about fixing this string and instead resurrect one of the old strings with a separate power lead to light the unlit part of your tree. Your family, insurance company and local emergency services would all thank you if they knew . . .

Brother I feel your pain. You sound like you are on your last nerve. Hey, many days left 'till Christmas, lets work it out. There are so many variations of the trees that you describe it is difficult to help. Some common points. In the USA they have to meet UL specs and probably have a fusible link for each circuit. If the bulb you describe is the fusible link maybe something is wrong with that circuit. Examine it carefully for shorts. Look for physical damage. The three wires are a common way to complete the circuit if a bulb fails. Calm down, look at the tree with fresh eyes and report back. There are some Non UL ways to fix this but I would suggest them for academic purposes only.

Tom

IanM wrote in news:hev9h6$2lct$ snipped-for-privacy@energise.enta.net:

I have met the dreaded fuse-bulb and have been defeated.

My soultion was to carefully unwind the SIQ from the 6 branches it was "installed" in. I put the brancehs back on the tree, connected a string of similar number bulbs, and draped them over the branches. Since the brancehs were the top tier just below the treetop, it is hard to detect any less density of the rpelacement string, even though it has fewer bulbs.

All is well again and I thank all who replied with timely and accurate answers.

Happy Holidays

PS My wife went out looking for a new tree today and she concluded that our tree has a better shape and density than anything else she saw, so it looks like more unwinding when strings fail to light on the tree. This time I'll use LED lights. So far they seem to look nicer and should hold up longer than the old minibulbs.

I'm glad you have found a workable, safe solution. However it looks like improved light testing skills are in your future in the interests of domestic harmony.

DONT let blown bulbs accumulate in any string or the fuse bulbs will fail sooner. You can probably 'nurse' what you have for a couple of seasons. A torch battery of a suitable voltage (a bit less than the bulb's working voltage) wired with a small series resistor (protection against the auto-shorting 'feature') to a socket taken from the dead string makes a far better bulb tester than trying them 'live' in circuit. The tester must actually light the bulb as the shorting device gives misleading results with common circuit testers. It turns bulb testing into a much simpler chore.

The other useful gadget for testing is a bulb base, glass removed with two leads with plugs to suit your multimeter going to the two contacts. Its used with the string disconnected and it lets you measure resistance between any bulb socket and the supply terminals of the string in both directions to quickly locate sockets with bad contact to the bulb or failed bulbs that haven't shorted.

For about 20 years from the 70s to the 90s I kept several WW2 vintage Osram strings in safe and good working order until I couldn't get any compatible bulbs any longer. The pre WW2 string was scrapped for spare sockets circa 1990 to keep the other strings in safe condition. I'd bet I could get one of those string going nearly 20 years later without much hassle. The old bulbs were much better than those produced after the mid 80's and usually outlasted several replacements even though they were ancient when I inherited the lights.

I'm not so sure the LED strings will last well. Chinese crap built down to a price, designed for minimum parts count not lifetime. They mostly over-drive the LEDS to save a few cents on brighter ones and they are usually NOT replaceable. There have to be some better ones out there as I see some used for decor effects 365 days a year, but I'd bet they have a premium price and without going to a specialist supplier you will probably get ripped off. I don't see any free or very cheap extended warranties on the LED strings either ;-)