Multiple Leds in Series and 1 burned out

I opened up this LED bulb that I got and burnt out a few days ago. I cracked it open and tested the individual LEDs and they work, except one which had a noticeable black spot in it. So I tried to desolder it, which didnt go so well but I managed. I figured if I put a blob of solder over the 2 plates, the electricity would flow and Id get the others to light up.

Alas that did not work. Here is what it looks like now. Each individual led works.

IMG_7501.JPG

I am not surprised. If you had subjected it to such trauma that a LED visibly burned out, and since they are all in series, then whatever you did had by definition overloaded all the LEDs to the same degree. While they may all "work", you may find that they require a much higher current that before, or possibly a higher voltage.

As always - you have provided grossly insufficient detail. You require something of the order of 48 V to power it; what are you using to do this and what are you using for current limiting?

Contrary to Grumpy Mike's recurrent complaint, these units frequently use series strings of two paralleled LEDs. This one clearly does is an exception.

Maybe it's just the lighting, but it looks to me like some of the other lights have black spots on them.

My guess is it was exposed to a massive overcurrent event. Since they're all in series, it is likely that more than one of them were damaged. Throw it out and buy a new one, that doesn't look like it could possibly cost more than a few bucks.

Also, rest the soldering iron on LEDs sideways, after putting a big blob of solder on each side. After 5-10 seconds, the whole thing will come off. Since they're those plastic carriers, it'll smoke and stink, and the thing you get off will not be recognizable as an LED afterwards. That's a pretty easy way to take off 2-pin SMDs - get enough solder on the ends that the iron touches both ends at once.

Paul_B

Sorry you didnt think I provided enough info. I dont know what other info I can provide. I simply took apart a burnt LED bulb and wanted to test it.

We do have a lot of powerouts and power fluctuations in HN so its very probable they were burnt out during one of those events.

So what you are saying is that at best I could use them as individual SMD LEDs for some project, but they arent going to work unless I pump a higher voltage into them because they are in series.

Thats ok, Ill save them for parts. I wasnt looking to do anything with it. Just tinkering.

Thanks

Right, so if it was in a LED bulb, what about the other components in the bulb - presumably, a capacitor, a resistor and a bridge rectifier? It is almost certain that they would be damaged as well in order for the LEDs to be damaged. In fact, it could be a failure of those components and not necessarily a power surge, though that certainly is a possible primary cause.

And both DrAzzy and myself are suggesting that it is likely that all of the LEDs are damaged in some way and not particularly useful.

So I imagine that when you say "Alas that did not work" but "Each individual led works", you mean that you tried reconnecting the disc to the other components in the bulb. I was wondering what you meant - and failed to explain. That is precisely the "not enough info". Does that not immediately tell you that it is the other components that have also been damaged?

No it doesn't. I'm learning this stuff. :-). I'm a biochemist.

OK, sorry, I actually missed out on your original description where you did say that you had disassembled a LED bulb. :confused:

The point here is about "cascade" faults - what you observe is not the primary fault, but the result of at least one other failure.

We get a number of such enquiries here about broken Arduinos and when it involves excess voltage applied at some part of the power supply, the general advice is to consider that the board is no longer serviceable and any further use of it must be considered conditional - if it works, OK but do not use it in any situation where subsequent failure will be of any concern whatsoever and do not consider it to be a potential source of spare parts given the same caveat.