LED working only when connecting multimeter in continuity mode!

[Antoine]

Hello everyone!
I have been surfing this forum for some time and finding great answers so thanks to everyone for that!

I finally registered because i have an issue i can't find the answer to just researching the forum.
I finished building a Honey Bee clone (Aion Procyon) and it works fine and sounds great, except for the power LED which doesn't turn on.
The associated resistor value is 4.7k. I've checked the components and the soldering and it seems fine.
The weird thing is that, when checking for continuity, I noticed the LED does turn on if i connect the multimeter through the LED (like checking the continuity through it). I really don't understand in what way connecting the multimeter could have an influence on the circuit..
If anybody has some explanation, i'd be really happy to hear it!
Cheers,
Antoine

[antonis]

Hi & Welcome..

Could you plz be more specific about connecting DMM "through" the LED..??

[DIY Bass]

In continuity mode you meter is putting out a voltage and measuring whether or not that voltage appears on the other lead.  If it does then you have continuity.  If you put that voltage across an LED (with the correct polarity) then the LED will turn on - same as if you put any voltage across an LED (standard disclaimer about the voltage being too small or too large).  Essentially you have proved the the LED works and that the reason it is not turning on is a wiring fault (or you damaged the switch soldering it - been there done that).

[Antoine]

In continuity mode you meter is putting out a voltage and measuring whether or not that voltage appears on the other lead.  If it does then you have continuity.  If you put that voltage across an LED (with the correct polarity) then the LED will turn on - same as if you put any voltage across an LED (standard disclaimer about the voltage being too small or too large).  Essentially you have proved the the LED works and that the reason it is not turning on is a wiring fault (or you damaged the switch soldering it - been there done that).

Thanks for the answer!
You're right, i had the idea and tested a spare LED, it didn't light up but because i had the wrong polarity!
Now i have to figure out what's wrong with the circuit..

[Antoine]

Hi & Welcome..

Could you plz be more specific about connecting DMM "through" the LED..??

[Antoine]

In continuity mode you meter is putting out a voltage and measuring whether or not that voltage appears on the other lead.  If it does then you have continuity.  If you put that voltage across an LED (with the correct polarity) then the LED will turn on - same as if you put any voltage across an LED (standard disclaimer about the voltage being too small or too large).  Essentially you have proved the the LED works and that the reason it is not turning on is a wiring fault (or you damaged the switch soldering it - been there done that).

Found the problem! The square and circle markings for the LED on the PCB are inverted. I switched it over and it works now ! Thanks guys!

[anotherjim]

I think there's always a chance of confusion with any kind of diode polarity markings. A common one is a "+" denoting the cathode! I think this one come comes from thinking of diodes as rectifiers - there would be AC in on the anode and +DC out of the cathode!
It pays to doubt the PCB marking and, as you did, confirm with DMM continuity.