how to troubleshoot LED Christmas strings
Hi! I have several strings of blue LED Christmas lights that either don't work or are incredibly dim. I have a collegiate diploma in electronics even though I don't work in that field anymore, so I started troubleshooting them to discover why they fail so frequently. They consist of two 35-light strings end to end on a single cord, and have no electronics because I can "see the sine wave go through them" so to speak.
So I thought I could check them with a multimeter, but on the diode setting I get an open circuit both ways, and I checked with a regular LED and I get .7 volts direct and open circuit on reverse, so I know my meter is good. However, on these Christmas LED's, the only scale that registers anything is the 20M ohm scale, where I initially get 65 Megohms, that tapers down to 17.2 in one direction, and 10 Megohms, that tapers down to 3.8 in the other direction, which seems to indicate that they contain some capacitors. However I ground one socket down only to find it only contains a tiny LED molded in plastic with a lens fitted over the LED.
Is it possible that these LED's don't work as regular LED'S since they are made to work on AC circuits (neither the plugs nor the wires have any integrated components of some sort) and if so, would anybody know how I could troubleshoot these strings to replace the failed LED's? At $20 a string, it seems to me they should last more than three years. Thanks for your help.