After years of use, my favorite Fat Max rechargeable flashlight stopped working. There was no warning, no dimming or flickering; one day it just wouldn't turn on. I was bummed because it had been a dependable tool. The rugged, waterproof case made it perfect for throwing a bright beam of light to check the creek-level during storms or to see what was making that noise along the fence-line in a blizzard.

Based on past experiences I anticipated that repairing the flashlight would be more expensive than buying a new one. Luckily, the problem turned out to be easy to diagnose and simple to repair. Even better, I already possessed all the tools and materials required.

Supplies

Screwdriver to disassemble the flashlight.

Cutting pliers (snips) to cut the broken electronic component

Soldering Iron and Solder to attach the new electronic part

Drill and Bit to create a new hole for wiring

Small File to enlarge one hole and smooth another

Magnifying Glass to better see the small electronic components

Containers to hold and organize screws and parts during the repair

Latching Pushbutton Switch with wiring tail to replace the broken part (preferably waterproof)

Although I didn't need them for this project, having the following tools is always a good idea when starting an electronics project.

A basic Multimeter to test for voltage and amperage, resistance and continuity

An Alternative Power Source or Batteries

Some Heat Shrink Tubing to insulate electrical connections

A set of Driver Bits for the ever-expanding types of fasteners

Miscellaneous Pliers and Tweezers and Spudgers are always good thing to have available

Step 1: Finding the Problem

My first thought was that the rechargeable batteries had died, or maybe the charging circuit had failed. Those are common problems with rechargeable devices. And that was bad, because buying replacement battery/charger parts is often as expensive as buying a new flashlight. But just to be sure, I took the flashlight apart to see if I could find a part number that I could look up and determine if I could replace them easily and cheaply.

Plus, I always disassemble broken items simply to see how they work and how they are made, maybe even learn something in the process. I can't always fix a broken device (sometimes can't even find the problem) but it's always educational and entertaining to see what's inside them.

While taking the flashlight apart I accidentally triggered something, and the light came on. It was still very bright and appeared to work fine. So, the batteries were obviously not at fault. I started looking for the real cause of the problem. Whenever I squeezed my hand around the main assembly, the light came on. Obviously, there was a loose connection somewhere. I started squeezing and poking on smaller and smaller portions of the assembly, narrowing down the location of the fault. It didn't take long to find the actual point of failure. A magnetic reed switch had broken.

The Stanley designers had used magnetically controlled reed switches to avoid penetrations in the case. Instead of piercing the case with mechanical connections, the designers had used magnets embedded into both the On/Off switch and the dimmer-knob. These magnets were strong enough to trigger the reed switch through the plastic case. This allowed the entire case to remain a single watertight enclosure with no pesky holes drilled through the skin.

The reed switch is very small, and I had to use a magnifying glass to determine that the glass tube surrounding the switch had shattered and the switch no longer responded to the magnet. I didn't remember dropping the flashlight, so I don't know why it shattered. It might have broken a long time ago and the reeds finally separated, or a piece of glass might have gotten wedged between the reeds.

However, I noticed that the both reed-switches for the dimmer-control had foam rubber pads between them and the PCB. But the broken On/Off reed-switch did not have a cushioning pad. That might explain why it broke while the other two remained intact.

I could still manually move the exposed metal reed until the two ends contacted and created a complete circuit. When I pressed them together, the light still came on. I tested with a gigantic neodymium magnet and I could make the reeds come together. But neither of those options, giant magnets or poking with a finger, seemed like a viable long-term solution to me.

Step 2: Creating a Solution

Now that I knew what the problem actually was, I just needed to fix it. I have reed switches in my parts bin, so for a moment, I considered replacing the broken one with a new one. But to be honest, I've never had much luck with reed switches unless I am designing the project from scratch. Magnetic reed switches are great for science experiments, wonderful for making mystery/magic/gag devices, or something like a toy burglar alarm or sensor. If you can control the magnet and reed-switch and are free to place them in any orientation at any distance required, they are easy and fun to use.

But every time I've tried replacing one in a commercial product I have gotten bad results. Getting the magnet and reeds perfectly matched and aligned within the constraints of an existing configuration seems to be beyond my capability. So I decided to find another solution.

I thought about drilling a hole through the case and installing a button or switch in place of the reed switch. A big honking toggle switch with a safety cover would look really cool. But I hated to make holes in the case and destroy the waterproofing. Being able to wander around outside in a drenching downpour was one of the main benefits of the Fat Max design.

After seeing how tightly and precisely packed the guts of the flashlight were, I also thought about discarding the shell and using just the guts of the flashlight as a cool desk lamp or hanging task-light. The guts were a big solid hunk of industrial goodness that slid out of the protective shell as a single assembled unit. Suspended on cables from the ceiling it would look very chic. But I really needed a rugged, long-throw flashlight for use around the property more than I needed a decorative task light.

So I returned my attention to finding of a way to repair the flashlight. As I studied the configuration and assembly, I discovered other challenges to redesigning the button location. The Stanley designers had packed the inside of the flashlight so tightly and so precisely that there was really no room left to add another button. There simply wasn't room for even the smallest button, so any new button would have to be mounted completely externally. It was an impressive feat of design, but really annoying for a tinkerer.

Also, since the internals of the flashlight slid out of the housing as a single unit, I could not add a switch and run the wire through the case without causing myself a bunch of headaches. If I mounted an external button and ran the wire through the case, I would have to cut and then re-attach the wiring every time I disassembled the case. Plus, I would need to mount the button to the case and the fasteners would create even more holes in the previously waterproof housing.

The only reasonable place to add a new penetration was through the back plate of the flashlight, where the charging port was already located, and the only place a channel between the outside world and the interior of the flashlight existed.

Step 3: Installing the Fix

Now that I knew where the button was going to be located, I could look through my switch and button collection. I salvage parts from all the devices that I can't fix, precisely for situations like this. I was sure I would have something that would work. I found several candidates, but this time the best solution was actually a new switch that I had bought for another project.

I needed a toggle switch or a big latching button, the type that stay on until you turn them off. It needed to be waterproof or have a waterproof housing. And it needed a wiring tail long enough to reach into the case and connect to where the reed switch used to be. I also wanted it to be easy to operate when I was wearing gloves, so no tiny slide switches. But every scavenged switch in my collection that met these cirteria were all panel mount and so large that they hid the charging port.

Finally, I decided to use a latching button that already had a semi-waterproof housing and long leads that I had bought from Adafruit. The wiring pigtail was long enough that the button hung a good half inch away from the back plate which iallowed me to move the button out of the way when charging but didn't get in the way when using the flashlight. I've used the same button in previous projects so I knew it was rugged and reliable for long-term use. And it has a nice solid click to it so it would be easy to find and operate in the dark while wearing gloves. Only the wires needed to penetrate the waterproof case, so the hole would be small and easy to plug with a dab of silicone. (Amazon has some multi-packs of similar switches here and here (affiliate link))

To test it, I simply wedged the bare ends of the button's wires under the leads of the broken reed switch. I clicked the button on and off several times and everything worked, nothing got hot and there was no smoke.

I clipped away the broken reed switch but left as much of the leads as I could so I would have something to solder to. I enlarged a hole in the back panel of the case and ran the leads of the button through the hole and through an existing hole in the charging port's PCB. Then I soldered the ends of the button's leads to the remaining leads of the reed switch.

I tested the button after the soldering, and it still worked. So I reassembled the flashlight and the case and the caps and tested it once again. The light still worked great. The button was easy to get to and use, but stayed out of the way and it was easy to move it out of the way to plug in the charger.

With a few minutes of work and one new part, I once again had a bright and still somewhat waterproof flashlight to use on rainy nights. It's not perfect, it's a little more delicate and awkward than the original. The button definitely looks hand-done, but adorably so. Like a cute hand-sewn patch on the knees of your work pants. Let's say it adds character and smile about it. And it's certainly a lot better than throwing away the entire device because one small part had failed. I call that a success.