Repair Stanley Fat Max Flashlight Reed Switch

After years of steady usage, my big powerful Fat Max rechargeable flashlight suddenly stopped working. I was bummed because it had been a dependable waterproof tool that had thrown a bright beam of light for a quarter mile or more; just the thing for checking the creek level during storms or to see what was making that noise along the fence-line.

The front lens and bumper screw off and the internal components slide out as a single unit. A plastic end is held in place with three screws. When you remove that end cap you can also remove all the internal components. 

I thought the rechargeable batteries had probably died so I took it apart to see if I could replace them. While taking it apart I accidentally triggered the light. It was still very, very bright. The batteries were obviously not the problem, so I started looking for for the real cause of the problem.

It didn't take long. A magnetic reed switch had broken. The Stanley designers had used reed switches to avoid making penetrations in the case. Magnets in the On/Off switch and the dimmer dial triggered the reed switched through the plastic case. It was an unexpected feature and I  thought it was a nifty design.

There is no hole under the on/off or dimmer switch. Instead, the reed switch senses the magnetic force directly through the plastic. Only the front and back of the case have openings, and they are both well sealed when the flashlight is fully assembled.

The On/Off and dimmer switches hold magnets, but neither penetrates the waterproof case..

The magnets in the On/Off and dimmer switches are strong enough to trigger magnetic reed switches that are mounted on their own PCB directly above the switch, At lower center is the broken on/off reed and the two at the upper edge of the board are for the dimmer switch. Note that both of the intact reed switches have rubber pads underneath while the broken one does not have any cushioning, 

The glass tube surrounding the switch had shattered and the switch no longer responded to the weak magnet in the on/off switch. I didn't remember dropping or impacting the flashlight, so I don't know hy 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. 

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

The glass tube surrounding the reed switch had shattered and the switch no longer responded to the magnet of the on/off switch.

This is what the reed switch is supposed to look like. Notice how the two leaves (reeds) are slightly separated. But when a magnetic force is applied, the two metallic reeds are drawn together to form a complete circuit.

I could still manually move the exposed reed to form a contact and the light still came on. And a big neodymium magnet could make the leaves move together. But neither of those options seemed like a viable long-term solution to me.

Now that I knew what the problem actually was, I just needed to fix it. I have reed switches in my parts bin, and 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. They are great for science experiments, wonderful for making mystery/magic/gag devices, or maybe a toy burglar alarm. 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 seems to be beyond my capability. So I had to find another solution.

I thought about drilling a hole through the case and mounting a button or switch in place of the original. Or maybe placing a switch somewhere else. But I hated to add holes and destroy the waterproofed case. Being able to wander around outside in a drenching downpour was one of the main benefits of the Fat Max design. And after seeing how tightly packed the insides of the flashlight were and realizing that the entire contents were a single object, I could not think of a way to mount a dependable switch that didn't require me to rewire the switch every time I took it apart. The only existing penetration in the case was at the back end where the charging port came through. That seemed like the best bet for adding a new switch, if I could find a way to get the switch out of the way of the charging port.

I also thought about using just the guts of the flashlight and turning it into a cool desk lamp or hanging task light. The guts were a big solid hunk of industrial goodness. Suspended on cables from the ceiling it would look very chic. But I really needed a rugged, long-throw flashlight for around the property.

After looking through my switch and button collection. I wanted a toggle switch or a big latching button, but they were all panel mount and so large that they hid the charging port. There simply wasn't room for them. Finally, decided to use a latching button that already had a semi-waterproof housing and long leads from Adafruit. It allowed me to move the button out of the way when charging, and it has a nice solid click to it so it would be easy to find and operate in the dark.

(Amazon has some multi-packs of similar switches here and here (affiliate links))

I had a latching button that was perfect for an on/off switch. It was encased in a semi-waterproof case and had two long leads already installed.

I tested it by wedging the leads under the remains of the red switch leads.

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 plastic 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 snipped off the remains of the broken reed switch, but left as much of its metal leads as possible so I could easily solder the hew switch to them.

I routed the wires for the new switch through a widened hole in the back end cap and then through exiting holes on the PCB for the charger port. I made sure to leave enough wire so that the button could be moved out of the way during charging, but not too long that the button became obtrusive.

I soldered the button leads onto the remains of the reed switch and slid the entire assembly back into the body of the flashlight.

The new button has a nice feel when clicked, is easy to find and operate in complete darkness, reasonably waterproof, and stays out of the way when recharging the batteries.

I reassembled the flashlight and tested it. The light worked great, the button was easy to get to but stayed out of the way, and it was easy to plug in the charger. With a few minutes work and one new part, I once again had a bright and still somewhat waterproof flashlight to use on rainy nights.

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