noob: blue LED polarity

[Burnincoils]

Dual Mono 3886 kit ordered recently


alright i think i installed the blue LED backwards.


the long leg against the ">" arrow

from what i understood of the guide:
"arrow ">" this points towards where the long leg is soldered in.

multimeter gives reading(1.960) only when reversing the testing leads and dont light up LED.

when i was soldering the LED lit up briefly lol

is this a problem? is there another way to test it?

thanks

 

[counter culture]

A good way of testing LEDs is to use a lithium coin cell such as a 2016. I have dozens around here as I bought a batch of 50 keyring torches from dealextreme.com to use as doglights.

You can connect the LED momentarily directly across the coin cell. They have ~3.6V out which is sufficient to cause any LED to strike, but so little current drive capacity that destruction of the LED is unlikely unless it has a VERY low power rating, I've never blown one up doing this.

 

[Burnincoils]

hey counter culture,

nice tricks!(they are avaliable everywhere) i will try them for sure, but i'm more inclined to just cancel the led.

can i install a jumper wire instead?

here you can see a picture of the led i removed just now

the long leg supposed to go on the left against the arrow?

 

[Mooly]

If the LED is just purely cosmetic then you can just omit it with no further action.
You say the LED lit while soldering ? You soldered with it powered up or with the caps fully charged ? If the iron was earthed then you could have a low resistance path via the iron that zapped the LED.

 

[Burnincoils]

the board is not in a condition to be powered up still

no the boards still not wired to ac.

i just saw briefly a blue flash reflected off the worktable

the iron is 2 wire so maybe its not earth? strangest thing... anyhow yeah i will check if it is cosmetic then i dont need this.

maybe the tip is somehow carrying voltage? (no idea about this making sense or no)

 

[Marra]

Leave it out and whatever you do do not install a jumper wire unless you mean to connect to an led on the front panel.

 

[AndrewT]

That little white arrow seems to be non standard.
A LED is a diode. We usually find diode symbols and orientation to be quite unambiguous.

The LED symbol with a part circle with one flat edge is used. That flat edge corresponds to the bar of the diode.

 

[Burnincoils]

alright thanks guys, i will not install jumper and just cut it off and if the boards not working(after ac on) i'll update so we find a solution.

 

[pdul]

Looking at the closeup it seems that you just have to turn the led around to get + on the long leg.

 

[pdul]

It is very clear that you have + on the series resistor

 

[Mooly]

the board is not in a condition to be powered up still

no the boards still not wired to ac.

i just saw briefly a blue flash reflected off the worktable

the iron is 2 wire so maybe its not earth? strangest thing... anyhow yeah i will check if it is cosmetic then i dont need this.

maybe the tip is somehow carrying voltage? (no idea about this making sense or no)

Leakage from an iron can happen but it would need the PCB to have a return path somewhere. Might be worth measuring the AC voltage on the working iron to a known mains ground point. If you do read any voltage then I have a hazy recollection that the leakage current should be under 5 micro amps for a good iron.