I'm just getting started with electronics and so for a simple project I tried to desolder the LED from a garden solar light in order to attach a female header (I trimmed it to 2 pins). My intention was to use the header as an easier way of experimenting with different 'loads', with the benefit of being easy to plug the LED back in when desired.
But after desoldering the LED and soldering on the header, when I attach the LED to the header it doesn't light (the battery was disconnected when soldering).
The voltage I measure across the header with the LED plugged back in is 1.26V, but in series with the LED I measure no current. When the LED is not connected, I measure a current of 46mA across the header.
(the original 1.2V 2/3AA Ni-MH battery is connected when measuring)
(the LEDs that were removed all work in a separate circuit, so the LEDs are not damaged – at least not obviously to me)
Another unmodified light I bought at the same time measures 1.2V across the LED and a current of 3.46mA.
I think I've damaged the circuit somehow (I suspect whatever is underneath the black blob), but I'm not sure how to diagnose the problem. Are there any tips I can follow here?
Could it be that I applied too much heat during soldering and the circuit was damaged? It is a small board and so I guess the heat isn't spread out a lot.
Thanks.
The inductor shown below is 56uH (green-blue-black-silver) and I measured its resistance to be 3.5 ohms (using the resistance setting on my multimeter).
Best Answer
These boards have five parts. The led, a axial inductor (the green resistor looking thing, likely 100 milli Henry), the solar panel, a NiMH battery, and the IC (Chip on Blob, it's just a common solar panel led boost driver).
Too much heat could certainly have damaged any of these parts. Assuming you disconnected the battery before soldering, the most likely part damaged is the IC bond wires. The inductor is easy to test, just measure it's resistance. This would be enough to know if it is open or not. Use the good boards inductor as a reference.
Other things to check. Battery should be above 0.8 Volts or the IC won't turn the led on. It's a under voltage lockout to prevent the battery from being drain to death. Measure the solar panel under light and load, like 470 ohm resistor. It should provide 2+ volts under full light. Compare that to the working boards battery and panel.
Consider it dead, it only cost you a dollar or so.