Troubleshooting LED light issue

[MattM]

Hi,

I have been asked to have a look at a LED Christmas light string on a 2ft snowman. It is a basic LED string wrapped around a wire frame.

The PSU is a 240v stepdown to 24v 580ma 10.4VA.

The voltage at the string appears to be fine but the string won't light. The string is not open circuit. I was told that it lit for about 30 minutes and then failed and has not come back again.

I am guessing I have a duff LED/resistor in the string but have no idea how to fault find this easily. If it was AC I would have used a tester pen at each LED but clearly I can't do that as it is DC.

Any suggestions would be gratefully received.

Thank you

[stj]

Re: Troubleshooting LED light issue

i use a pair of syringes used as needles to poke through the insulation onto the led legs - then short them to bypass the led.

most common failures for me where blue - for some reason, as they in theory have the higher operating voltage.

[MattM]

Re: Troubleshooting LED light issue

Thanks very much for this, will give it a go

[MattM]

Re: Troubleshooting LED light issue

I spent some time with this and established that the PSU was in fact at fault along with a bridge rectifier which was inline with the cable to the lights.
I removed the bridge rectifier and the unit now works but the lights flicker presumably because the bridge rectifiers is not in series.
It was installed inside a weather proofing fitment and I had to cut it out. It is a DB107S. What I don't know though is what the wiring diagram for it was as I had to cut it out. Has anyone any ideas and if I simply leave it out is there any risk to lights - the flickering isn't that bad?
Thank you

[CapLeaker]

Re: Troubleshooting LED light issue

add a capacitor? What does this thing look like? Any pics?