I cleaned off what I could of the solder on the removed electrolytic capacitor, and manually soldered it back on to the board, using Blu-Tak to steady the side as I did so.
I de-soldered the dud LED, and checked it afterwards - it really is dud. I checked a new one, which lit, and soldered it into place, again using a tiny bit of Blu-Tak against its side. Now it doesn't light. Hmmm - methinks my logic is off, possibly because of the rest of the circuit. I just can't believe this LED is as dead as the other after simply soldering it on. Unfortunately I don't have a 12V supply with which I can check this part of the board, which is the power circuit.
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It is quite likely the circuit stops it lighting. With no power the series resistor is effectively in parallel. If it is a low enough value it will prevent the voltage getting high enough to light the LED. Green LEDs need about 2V to light up. Anything less and they don't light at all, unlike a bulb which would just be dim.
ReplyDeleteI think LEDs are particularly sensitive to temperature. In fact they are the only devices I can remember damaging myself, and I have been hand soldering for 38 years!