Expert: Master Bob - 12/6/2004

Question
A string of my mini christmas lights are not working. I have a bulb tester and every bulb seems to be good. So how do I test the sockets to see where the problem might be?

Answer
Hi Jeffery,

 Sorry just responding...had to replace the cooling fan/ heatsink assembly in our main computer system tonight...took a little longer then expected - just getting it all back up and online.

 Bad Christmas light strings are pretty common...seems like every year we have a set that's not working when they were all working when we put them away. Strange how that works...

You didn't state what type of Christmas lights you have- and there are several dozen different configurations...some screw in...some snap in. Most newer sets are now fused - with a small fuse right up at the plug (does yours have this feature..?)

 The bulk of light strings are wired in series ( I haven't seen one that wasn't) so that if one bulb or socket is bad - none of the lights work....because the electrical path is interrupted. What we've found very handy for testing this is a "voltage detector stick" ( a handheld tester that looks like a fat pen...ticks and lights up in the presence of voltage...most hardware stores sell them for ~$10 )...you can run it down the string until you find the area that shows no voltage...and you found the bad bulb or socket area. These work for troubleshooting most light sets...and they are also handy for checking other circuits around the house as well (I don't travel without one - keep one in my shirt pocket...lets me know ahead of time when a circuits live or dead...without having to undo any connections).

 Without knowing which type of light string you have...that's what I'd recommend for troubleshooting.  I've been able to find and fix all our light strings using one of them. (we use a red GB GVD-504A "Circuit Alert" (item #300343 at Home Depot for $9.95) - but other brands work equally as well)

 Hope this helps...if you need more details, please follow-up with what type/model of light strings you have...just far too many different types on the market.

Best Wishes,

Bob Osgood
Master Electrician

RKO ELECTRIC

www.rkoelectric.com