Ambika voicecard: burnt note LED [solved]

I’ve assebled 3 voicecards which were working fine, but on one voicecard the note LED stopped lighting. I mesured 5V on this led while it should be 1,8V. Any suggestions?

Is the voicecard supposed to receive a note? Does it play sounds?

Yes, I receives notes and plays sounds.

https://dl.dropboxusercontent.com/u/49267129/IMG_1540.JPG
https://dl.dropboxusercontent.com/u/49267129/IMG_1541.JPG

Maybe the LED was damaged by too much heat when you soldered it?

I don’t think so. As I mentioned before, I measured the voltages on the note LEDs, while I let my sequencer playing a long note, and the voltage on the damaged LED was 5V, while the voltage on the others was 1,8V.

This means that no current is flowing through the LED. Which means it is damaged or badly soldered. No?

You’re right, so I just need to replace the LED.
It’s damaged, it doesn’t light in the diode-test mode of my multimeter. Is it possible that the voltage is to high for the LEDs? Because all are lighting very bright.

LEDs do burn out. As a test you can touch another LED onto the pads and see if it lights up. Be careful though.

> Is it possible that the voltage is to high for the LEDs? Because all are lighting very bright.

What makes LEDs burn and smoke is excess of current; and the 470R resistor does a good job at limiting it. You measured the voltage on a working LED at 1.8V. Hooked to 5V through a 470 ohm resistor, that’s only 6mA of current. Some of the measurements given in the LED datasheet were taken at 20mA current, so they are actually not running excessively bright. Some LEDs can light much much brighter with even less current - the LEDs that come with the kits are actually categorized as “indication/low intensity” (as opposed to the ones used specifically for lighting).

A working circuit will not endanger the life of the LEDs!

There’s always a very small probability of a manufacturing defect; and in my own experience some LEDs don’t like receive heat for too long during soldering (I remember having damaged a few white LEDs when building some 4PM Shruthi, and a few times when obsessively soldering again and again some Shruthi LEDs to line them up correctly)

It could still very well be a bad solder joint to the ground plane… Just try to resolder it and see if it works.

And again, I learned something new. Thanks!

6581punk: it lights up.shiftr: there’s no hope for the LED, it’s dead. :frowning:

great you found what it was!

the new led is a bit bigger, but it works. one more voicecard and it’s complete!

https://dl.dropboxusercontent.com/u/49267129/IMG_1543.JPG