# LED was working, now dead



## BurntFingers (Nov 26, 2019)

I finished a build today. It was working great. I moved the pedals on my board around to do this one on and now the led doesn't work. The pedal still works as it should, just the light is busted.

Not sure if you can see it easily but it's down there in the corner.

One thing I did notice was this led was dimmer than my other ones, but I put that down to the led and nothing else since it was working fine.

Is it possible for me to have overheated the led, and then it just died later on after having current through it? Je suis at a loss.


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## Barry (Nov 27, 2019)

Have you checked that it's still getting voltage? If you don't have DMM handy just touch another LED to the terminals and see if it lights


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## phi1 (Nov 27, 2019)

I would first check the resistance from +9V to the Anode of the LED.  See the schematic.  This resistance should be the value of R101 (4k7).  This resistor limits the current to the LED.  If a very low resistor was soldered here on accident, then the LED could get too much current and fry.

FWIW, it looks to me like you might have the correct 4k7 resistor in that spot, but then again it's tricky for me to read the color bands.

Barry's advice is good especially if the resistance from +9V to the Anode is correct.  To measure voltage at the LED, use the DMM with one probe connected to ground, and the other connected to the Anode of the LED.

If all that seems fine, maybe it's just a bad LED and you can try replacing it (and quickly test by Barry's method).


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## BurntFingers (Nov 27, 2019)

phi1 said:


> I would first check the resistance from +9V to the Anode of the LED.  See the schematic.  This resistance should be the value of R101 (4k7).  This resistor limits the current to the LED.  If a very low resistor was soldered here on accident, then the LED could get too much current and fry.
> 
> FWIW, it looks to me like you might have the correct 4k7 resistor in that spot, but then again it's tricky for me to read the color bands.
> 
> ...



Well I just checked. With the effect engaged I'm getting a reading of 8.8v from +9v (red lead of dmm) to the anode of the led (black lead of dmm).

I'm guessing that means 8.8v is going to the led and killing it?


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## phi1 (Nov 27, 2019)

Hmm no...

read my post again for where to hook up the leads to check voltage at the anode of the led. But the fact that it reads 8.8v from 9V+ to the anode indicates to me that maybe the led is already bad.

Did you check the resistance from 9V+ to anode?


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## BurntFingers (Nov 27, 2019)

"I would first check the resistance from +9V to the Anode of the LED."

I misread that, and measured the 8.81v from 9v+ to anode. 

From ground to anode ive got 2.56v showing.

I tried the trick from above to attach another led to the same terminals and I can't get it to light up if that's indicative of anything.


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## phi1 (Nov 27, 2019)

Weird, the only components in that branch of the circuit are the resistor and the led.  You measured 8.8v drop across the resistor and 2.56v drop across the led, which is more than 9v total, so that doesn’t make any sense.

did you try measuring the resistance?  If the resistance from 9v+ to the anode is good (4.7k), then just cut the wires to the led and wire in a new one.


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## BurntFingers (Nov 27, 2019)

Hmmm...lemme check the resistance before I finalise this other led. 

Thanks for your help.


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## Aria51 (Nov 27, 2019)

Time to get handy with a meter. I see splices in the leads so check them end-to-end for continuity.
With a meter set for diode test, test both directions across the led. It may actually light up a bit in one direction.
I think you should expect like 1.7v one way (and a little light) and something closer to infinity the other way. 

Have fun. I like fixing broken stuff.


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## BurntFingers (Nov 27, 2019)

phi1 said:


> Weird, the only components in that branch of the circuit are the resistor and the led.  You measured 8.8v drop across the resistor and 2.56v drop across the led, which is more than 9v total, so that doesn’t make any sense.
> 
> did you try measuring the resistance?  If the resistance from 9v+ to the anode is good (4.7k), then just cut the wires to the led and wire in a new one.



And 4.6k resistance. All things pointing to a crappy led in the first instance. I'll wire a new one in this afternoon.

Thanks for your patience with this.


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## BurntFingers (Nov 27, 2019)

And success. When I was in there though it turns out the 1uf cap was loose and causing the effect to cut in and out (in a bad way). Once that was resoldered and I spliced a new led on to the wires all is now good. 

I spent more time fixing this pedal than I did making it


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## moonlightpedalbuilds (Nov 27, 2019)

BurntFingers said:


> And success. When I was in there though it turns out the 1uf cap was loose and causing the effect to cut in and out (in a bad way). Once that was resoldered and I spliced a new led on to the wires all is now good.
> 
> I spent more time fixing this pedal than I did making it



Fixing time is the fun part ?


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