Pedal LED conundrum

Paul_C

One of the many pedals I own has an intermittent LED and I'm wondering if there are any suggestions what the issue might be.

It works fine to begin with once the pedal is switched on, but after a minute or so it starts to flicker and eventually cuts out altogether.

I've re-flowed various solder joints but no joy so far - any suggestions what it might be ?

Switch perhaps ?

octatonic

Have you tried replacing the LED?

Winny_Pooh

Do the legs of the LED possibly touch each other once back in the enclosure? 

Paul_C

octatonic said:

Have you tried replacing the LED?

I tried an LED that was lying around, but it didn't work at all, so I'm assuming I need something more specific (I'll contact the builder to see).

Winny_Pooh said:

Do the legs of the LED possibly touch each other once back in the enclosure? 

No.

lasermonkey

What pedal is it? With that info, and possibly a photo of the LED, we would be in a much better position to help.

Many manufacturers use different methods to mount their LEDs and these can all have unique issues. For instance, I was recently given an EQD Hoof to repair where the LED was intermittently going on and off. The way it was mounted meant that it was easy to push the LED back, which led to the leads shorting against the PCB. I simply pushed the LED fully home into its bezel and hot-glued it in place.

I have also encountered LEDs where the electrodes aren't completely encapsulated within the body of the LED which means they are free to short against the enclosure if mounted directly. Not one of my easiest troubleshooting sessions, I have to say.

We will be able to get to the bottom of this, but the more info you can give us, the better.

Paul_C

It's a Dwarfcraft built DeviEver BDSM. The LED is 5mm clear/white which glows purple.

I have removed it, cleaned the board where it connects and re-attached it with leaded solder.

I'll take some pics later and if I have time I'll check that there's still 9v going to it when it dies.

lasermonkey

Just had a look at a few pics of the BDSM. Firstly, the LED isn't mounted in a bezel, so it is feasible that one or both of the electrodes is intermittently grounding against the enclosure. Secondly, it's worth checking that the pads that the LEDs are soldered to haven't separated from their tracks. You'll need a magnifying glass to check properly. The LED could possibly have taken a knock. I've seen this happen before.

Paul_C

The red circle is where the LED connects. I put my multimeter on it while it was plugged in and got 9.83V from the power supply, 7.25V between the 9v in on the board and the hot side of the LED and 2.5V across the LED legs.

There's continuity between the LED hot and the power supply, and between the LED ground and the board spot marked LED (and the switch).

As happens every time, it works perfectly well for a minute or so and then starts to lose some brilliance before going very dim or cutting out completely.

I tried gently pressing the LED and wiggling it about while it was not working (but switched on) to no effect.

Once it's just about failed completely it does flicker on now and again, but nothing I did physically made this happen.

Paul_C

Update: I found some LEDs in a drawer which I knew worked and swapped one for the one in the pedal - success!

It's blue instead of purple, but it's no longer cutting in and out

I've got it sitting lower in the case so there's little chance of it receiving a blow, so hopefully that's that, for now at least.

lasermonkey

There are very few components in the LED circuit: the LED itself; the current limiting resistor (CLR) and the switch. Assuming that you have good continuity on the switch, all that remains is the resistor and the LED itself. Resistors tend to either work or not, though it might be worth checking the joints on the CLR. Otherwise, that leaves the LED. I have seen intermittently working LEDs, although it is rare.

You mentioned that you replaced the LED with another at some point. Is it possible that you inadvertently got it the wrong way round or overheated it? LEDs are surprisingly prone to heat damage.