I had this shake flashlight on my repair list for some time. Today I will troubleshoot the problem.
I attempted to load a video to show the problem but I found out that I can't embed a video unless the video is stored on a server such as utube and I don't have a utube channel. So I will explain the problem
The light will work when you depress the on button while shaking the flashlight. But if you press the on button and you are not shaking the flashlight, it will not light up.
This should tell you several things. 1) the LED bulbs is good 2) the wire coil is not broken (there are no breaks in the coil) 3) the circuit is intact and there are no faults with the components in the circuit used to light the LED 4) most likely fault is in the capacitor. I will go into a little detail as to how I arrived at these conclusions and the basis of how the flashlight works.
How the flashlight work
This flashlight has no battery instead it gets it's power from the coil of wire in conjunction with the movable magnet inside the coil. This is a result of induction. The magnet emits magnetic flux lines, these can be seen if you take the magnet and place a piece of paper over it. Sprinkle iron filings on the paper and they will reveal the flux lines. As you may have inferred these lines are polarized, they have a charge positive or negative. Just like the poles of a magnet. The wire is made up of a conductive material, in this case copper. The conduction is a result of floating electrons in the copper lattice structure. As you shake the flashlight the magnet is free to move inside the coil of wire. As it moves so does the magnetic flux lines. Due to the polarized charge of these flux lines they induce the floating electrons to move in the coil. This can be demonstrated by taking two magnets and placing them close to each other. If the poles are of opposite charge, they will pull together. If the poles are of the same charge, the will repel. Hence opposites attract and like repel. Now we look at the circuit. In order to get the LED to light we need a DC (direct current) supply. The voltage created by the magnet moving back and forth generates an AC (alternating current). So there is a rectifier or diode in the circuit. This diode only allows current moving in one direct to pass. This will work to apply pulses of charge to the capacitor. A capacitor is similar to a battery, the difference is that a capacitor does not generate power. It will only store power. The power that is stored in the capacitor will be use by the LED to cause it to light up. BTW LED is a light emitting diode. It is used in this type of flashlight because it requires less power than a halogen or an incandescent bulb. That is how these flashlights work.
Troubleshooting
Now we will start to troubleshoot before we disassemble anything. Start by observing the problem. As I noted, the flashlight goes on if you hold the on button down as you shake the flashlight. The light will not go on if you push the on button down but are not shaking the flashlight. Think about the problem and try to isolate the problem to a specific component. This is what I did by listing things I knew where working.
The LED went on so that tells me that the LED is not the problem.
The wire (and the magnet) are the source of the power. If the wire was broken there would no way for the power to be generated. Since the LED lit up when I shook the flashlight I can surmise that the wire / magnet were making power.
Since the LED lit up it also means that the components in circuit with the LED are operating and I assume are not related to the problem.
I suspect the capacitor is not doing its job because the charging system is working and the LED circuit is working. Recall the capacitor is used to store the energy (voltage) so it can be used later. The charging system appears to work so it should be charging the capacitor when the on button is not pressed. The on button appears to work as when we hold it down while shaking the flashlight the LED lights. So we conclude that the capacitor is not holding a charge or perhaps the circuit that charges the capacitor is open.
These are the basic steps to troubleshooting an electrical circuit. This is a very simple circuit but you can apply these troubleshooting methods to more complex circuits. The objective to troubleshooting is to limit the problem to small area and then concentrate on that area instead of wasting your efforts looking a the whole circuit.
Another good piece of advice is to examine the circuit board for any discoloration or any burnt smell. This could lead you to a burnt out component. Thanks for reading.