Why am I blowing out LEDs?

[CheapSuitG]

Built a pedal this evening, test fit in the enclosure but don’t tighten everything down. Fires right up. Woohoo!

Tightening everything down, midway the led turns off, won’t come back on. Pull it, test it, it’s dead.

Reason I keep power on is because it’s happened before, usually backing off a little on the nut I was tightening helps and the led turns back on.

What am I doing wrong? Replaced the LED 3 times tonight. The last time it was the footswitch. Before that was one of the pots. It seems to happen 2 out of three builds for me.

Am I shorting something out? My pots have pot condoms on them so there shouldn’t be a short there.

Also - the pedal works it’s just the LED.

Any help would be greatly appreciated.

 

[Erik S]

What kinda bezel situation we dealing with?

 

[Stickman393]

Thought:

If you're using a CLR on the cathode side of the LED, and your cathode is shorted to ground, then you'll no longer be current limiting that LED.

Shot in the dark.

 

[Cybercow]

Is there a CLR in place? Photos? Schematic?

 

[CheapSuitG]

Plastic and chrome

What kinda bezel situation we dealing with?

 

[CheapSuitG]

Yes there is a clr

It’s multiple builds.

They work fine out of the enclosure, it’s wgen I tighten down that they blow.

Is there a CLR in place? Photos? Schematic?

 

[CheapSuitG]

Would that fry the LED?

Thought:

If you're using a CLR on the cathode side of the LED, and your cathode is shorted to ground, then you'll no longer be current limiting that LED.

Shot in the dark.

 

[Robert]

Would that fry the LED?

Yep.

 

[giovanni]

Could it be that when you tighten the board the two legs of the LED end up touching each other and then shorting?

 

[Stickman393]

Could it be that when you tighten the board the two legs of the LED end up touching each other and then shorting?

That wouldn't fry the LED, though. It'd just cause the thing not to light in the moment.

Shorting the cathode to ground before the CLR, though, wil give ya the full 9vdc across the LED. That'll make the fucker real bright until it don't done go bright no mores.

Like I said: dunno if that's the case here, don't have a schematic or photos. But it's a possibility. Maybe tightening them pots leads to the cathode bending in such a way that it makes contact with something conductive that is connected to ground.

The opposite is also possible, if less likely: if the LED has an anode-side CLR and somehow the anode makes contact with the +9vdc rail.

 

[PedalBuilder]

Threads like this really need pictures.

 

[szukalski]

I thought this was a weird fetish thread.

 

[GAStan]

I thought this was a weird fetish thread.

Threads like this really need pictures.

Things that make you go "hmmmm".

 

[comradehoser]

In another discussion I was having troubleshooting why a PTP build's LED wouldn't light up, I noticed that the PPCB schematics variably indicate the CLR on the anode side or the cathode side.

Does it matter/is there a preferred best practice?

Personally, I always put it on the anode side in PTP because in my highly non-electrical engineering brain, that's the side that sees the 9v first (not sure that's true actually), but I'm sure that it doesn't really matter from the circuit's point of view.

 

[GAStan]

In a PTP build i would put the CLR as physically near the 9vdc source as practical. Reason being wiring is more likely to touch a ground than 9vdc.

On a PCB I think the physical layout of the board is the determining factor of where it actually is in the circuit.

I agree from a circuit's point of view it does not matter.

 

[CheapSuitG]

I’ll take pics tonight for this particular build.

It’s just happened on so many others that I thought I may be some step I’m missing/doing wrong.

 

[Barry]

When you tighten things up the legs of the LED may be bowing and hitting the bezel

 

[jwin615]

Are they coming out your anode or your cathode?
These may help if you mount them straight up off the board
100 for about a buck
Get 7.5, 8mm range iirc
Depends on your led height...

 

[PedalBuilder]

View attachment 92148
Are they coming out your anode or your cathode?
These may help if you mount them straight up off the board
100 for about a buck
Get 7.5, 8mm range iirc
Depends on your led height...

This is also a good use for the stripped insulation left over from the hookup wire.

 

[CheapSuitG]

Ordered.

View attachment 92148
Are they coming out your anode or your cathode?
These may help if you mount them straight up off the board
100 for about a buck
Get 7.5, 8mm range iirc
Depends on your led height...