Seasonal query! Bulbs faulty?

[paul243]

So as usual the outside Christmas lights have several bulbs out. When I remove one to check it a section of lights in the string also go out. When re-inserted the section lights but the bulb is still out. If I make a connection across the contacts within he bulb holder the section again lights up. I've tested the faulty bulbs with a meter and they all show continuity and look ok.
So- can the bulbs be bad but still make contact to keep the string alight? or am I missing something obvious?
Thanks

 

[flameport]

If it lights up, it's working.
If not, replace it.

They intentionally fail short circuit, so that the others in that section still work.
Testing them for continuity will reveal nothing.

 

[paul243]

Understood, thanks. Merry Christmas!

 

[davelx]

So- can the bulbs be bad but still make contact to keep the string alight? or am I missing something obvious?
Thanks

Indeed, as FP says, incandescent Xmas tree lights are to be designed to do this - the filament is constructed so as to hold apart two lightly sprung contacts. When the filament breaks, those contacts close to ensure continuity so that all the lights do not go out. They also have a fuse bulb at the start or the string ( with a white painted top) that does not do this so that if too many lamps fail the fuse bulb will blow thus protecting the remaining lamps.

If the fuse bulb blows, it's important to get the correct replacement, according to the number of lamps in the string.

 

[Harry Bloomfield]

You need to count the number of lamps which are part of just that string, then take along your dud lamp to a shop which sells such items. Best of luck with finding one, there are not many left. I left without a working lamp, it will stress the remainder of the lamps in that section of lamps and shorten their life, so needs sorting sooner, rather than later.

 

[davelx]

You need to count the number of lamps which are part of just that string, then take along your dud lamp to a shop which sells such items. Best of luck with finding one, there are not many left. I left without a working lamp, it will stress the remainder of the lamps in that section of lamps and shorten their life, so needs sorting sooner, rather than later.

Amazon has quite a range, down to 2.5V. Important to check that the bases match.

 

[Harry Bloomfield]

Amazon has quite a range, down to 2.5V. Important to check that the bases match.

and the current rating too, which will be embossed around the base.

 

[paul243]

Thanks all,
They are E12 12V 3W and seem to be available, ordered some from Amazon