Christmas light whole string is out, tests not helping

lumen aeternum

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Sep 29, 2012
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Before I put away the lights I replace the burnt out bulbs.
This string won't light at all. It was good when I put it up in December.
(miniature bulbs, about 2cm long that you remove from the plastic base & stick another bulb in, bending the wires around on the outside)

My continuity tester beeps all along the string, so I don't think its a broken wire. It should light intermittantly when I jostle it.
I looked at every bulb with a magnifying glass & removed, tested, replaced any dodgy filaments with tested good bulbs.
I even used the specialty tool to send a piezo current which is supposed to release any stuck shunts -- but unless the very first bulb has a stuck shunt, the bulbs upstream should still light.

Anybody got a clue as to this failure mode?

BTW how can you visually distinguish 2.5v from 3.5v miniature bulbs?
 

Lynx_Arc

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Sounds like a bad bulb somewhere to me. I would test each bulb individually or perhaps get a 12v power supply and cheap series sets of 6 bulbs till you find the bad "group" then you only have to check 6 individual bulbs.
And no, there is no easy way to know if a bulb is 2.5 or 3.5v other than comparing the output with a known voltage bulb.
 

brickbat

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Here in the US, these strings typically have a mini fuse in the plug. Might want to check for that...

Why don't you add your location to your profile?
 

lumen aeternum

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Now that you mention it... but the fuses are OK. Sure about the bulbs too. One bulb won't put out the WHOLE string, unless the shunt is stuck.
 

Lynx_Arc

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Now that you mention it... but the fuses are OK. Sure about the bulbs too. One bulb won't put out the WHOLE string, unless the shunt is stuck.
Basically you have to methodically test everything and you will find the culprit sooner or later. The Christmas lights I had never had shunts if one bulb went out the whole string wouldn't light and that included a badly placed wire not making contact on a socket when inserted.
 

Mark620

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Feb 22, 2006
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about xmas lights...the old incan miniature ones

if it is a single plug string - every other light is connected in series making a single wire loop - untwist one..

a double ended plug string -
50 light string the lights are connected sequentially in the string - usually in 1 section
100 light string the lights are connected sequentially in the string - usually in 2 sections, 2 wires on half and 3 wires on the other half
 
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lumen aeternum

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Yes this is 2 sections, but I don't think 100 lights. The fact that both sections are out is mysterious.
 
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