Since people seem to often have disagreement between them and their flashlight whether there shall be light or not I figured a troubleshooting guide could prove useful.
Therefore, for your convenience: Flashlight troubleshooting one-oh-one.
All brands, all models
Check the battery.
No, really: high power flashlight can easily run itself dry in less than an hour. Especially if you've been the battery before it can't hurt to take a brand new to try with. Most of the issues people have is with batteries anyway, not that everyone posts about it after discovery though.
Check the contacts.
See if the springs are okay and there is no debris in the threads or any other foreing material messing up the contacts. Doesn't hurt to wipe them clean and add a small amount of lube to any moving contact surfaces (like threads).
Incandescent lights
Check the bulb.
If it has any color (like blue) it's done for. Also pitch black is goner. Using a multimeter you can check for resistance between the terminals: some resistance is fine, infinite resistance is a burnt bulb.
Digitally regulated, microchip controlled, almost any led flashlight
Let the chip reset.
Take out the battery and leave the flashlight alone for a while. I've had a flashlight that would take over a minute while the spec said to wait for three seconds. Go figure QC on that.
Check the battery.
Yup, again. The electronics often like to perform most peculiar things when the voltage gets low. The "super saver offer" you got from a ebay or china could also be old stock and nearly dead to begin with.
4sevens Quark/Maelstrom, Fenix (practically all their tailcap clickies)
Tighten the tailcap's retaining ring.
Quarks and Fenixes have a plain aluminum colored ring with two notches in it. Maelstrom has a rubber hood over the ring, but it has cuts on the edge at corresponding positions. Using a needle-nose plies or a similar tool will help on tightening. Also you can try by-passing the tailcap with a paper clip to see if the light is functioning without the tailcap involved.
4sevens Quark, Fenix
Stuck on "head tight" mode.
Check for any conductive debris like machining chips in the head. If the outer rim is shorted to threads the flashlight can't recognize "head loose" position.
Nitecore piston drive models
Open up the light and clean the excessive amount of lube from the piston, body, and the O-ring. Then proceed to add small amount of lube in the O-ring and re-assemble the light.
Check the contact ring in the head and see if it's moving up and down smoothly. If it's not, cleaning and rotating it around might help.
Features. Albeit they might be annoying, they're more or less functions you can't get fixed
4sevens Quark, Fenix
The light flashes brightly and then drops down to the dimmer level when turned on (preflash).
Feature of the driver used, reportedly it comes as a side-effect for the high efficiency and dropping one results in losing another.
Light gets stuck on a mode when rapidly twisting the head between tight and loose.
Highly sophisticated computers can crash, resumes normal function once it runs out of power; see note earlier about taking off the battery.
Therefore, for your convenience: Flashlight troubleshooting one-oh-one.
All brands, all models
Check the battery.
No, really: high power flashlight can easily run itself dry in less than an hour. Especially if you've been the battery before it can't hurt to take a brand new to try with. Most of the issues people have is with batteries anyway, not that everyone posts about it after discovery though.
Check the contacts.
See if the springs are okay and there is no debris in the threads or any other foreing material messing up the contacts. Doesn't hurt to wipe them clean and add a small amount of lube to any moving contact surfaces (like threads).
Incandescent lights
Check the bulb.
If it has any color (like blue) it's done for. Also pitch black is goner. Using a multimeter you can check for resistance between the terminals: some resistance is fine, infinite resistance is a burnt bulb.
Digitally regulated, microchip controlled, almost any led flashlight
Let the chip reset.
Take out the battery and leave the flashlight alone for a while. I've had a flashlight that would take over a minute while the spec said to wait for three seconds. Go figure QC on that.
Check the battery.
Yup, again. The electronics often like to perform most peculiar things when the voltage gets low. The "super saver offer" you got from a ebay or china could also be old stock and nearly dead to begin with.
4sevens Quark/Maelstrom, Fenix (practically all their tailcap clickies)
Tighten the tailcap's retaining ring.
Quarks and Fenixes have a plain aluminum colored ring with two notches in it. Maelstrom has a rubber hood over the ring, but it has cuts on the edge at corresponding positions. Using a needle-nose plies or a similar tool will help on tightening. Also you can try by-passing the tailcap with a paper clip to see if the light is functioning without the tailcap involved.
4sevens Quark, Fenix
Stuck on "head tight" mode.
Check for any conductive debris like machining chips in the head. If the outer rim is shorted to threads the flashlight can't recognize "head loose" position.
Nitecore piston drive models
Open up the light and clean the excessive amount of lube from the piston, body, and the O-ring. Then proceed to add small amount of lube in the O-ring and re-assemble the light.
Check the contact ring in the head and see if it's moving up and down smoothly. If it's not, cleaning and rotating it around might help.
Features. Albeit they might be annoying, they're more or less functions you can't get fixed
4sevens Quark, Fenix
The light flashes brightly and then drops down to the dimmer level when turned on (preflash).
Feature of the driver used, reportedly it comes as a side-effect for the high efficiency and dropping one results in losing another.
Light gets stuck on a mode when rapidly twisting the head between tight and loose.
Highly sophisticated computers can crash, resumes normal function once it runs out of power; see note earlier about taking off the battery.
