fēnix® 3 HR: A Non-Destructive Teardown

Introduction

The Garmin® fēnix® 3 HR can be purchased either as a stand-alone watch or in a bundle. The bundle adds a heart rate monitor chest strap, the HRM-Run™, to the package. The boxes are similar, the bundle being the larger one. Here is what both boxes look like, front and back:

The HRM-Run™ chest strap monitor already comes paired with the watch in the “performer bundle,” which is a really nice touch.

There were some differences between the watch-only and the performer bundle packages I purchased. For example, the power supplies didn’t look the same. The form factor of the power supply included in the stand-alone package was new to me:

Inspection of the specs indicates they are designed to do the same job, the larger one being able to accomodate different wall power plug formats:

And a quick output check didn’t point to any significant differences.

Another curiosity was the fact that the bundled watch had some extra labeling on the bottom. Again, no harm done.

And as far as I could tell, the backlight brightness and color tone were very similar between the two.

Having two watches made it convenient for me to get a measurement of the height of the Elevate™ optical HR sensor bump on the back of the watch case. I measured the distance between the two watches’ back covers on the photo below as 3.1 mm. So the bump is about half of that: 1.55 mm.

Similarly, I placed the adidas® miCoach Smart Run over the fēnix® 3 HR, and measured about 4 mm between back covers. So the adidas® miCoach Smart Run watch optical sensor would be about 2.45 mm tall, almost a millimeter taller than the bump on the fēnix® 3 HR, although it seems to have a more stepped profile. I personally can hardly notice any of the two on my wrist.

The brightness of the LEDs seemed similar between the two watches and other optical sensors I own.

As a note, the adidas® miCoach Smart Run only has two LEDs, as opposed to three LEDs present in the Elevate™ sensor.

Wrist-based, optical HR sensors need a certain degree of proximity to the skin, and mechanical stability around the wrist, in order to accurately detect heart rate. That is perhaps one of the reason why most watches I have seen with optical sensors also have monolithic bands. The material used is typically silicone and the thickness is whatever the vendor considered necessary in order to provide sufficient mechanical stability to the watch over and around the wrist. And as a side-effect, typically you cannot easily remove them. Garmin® included a silicone band with the fēnix®3 HR that is not monolithic with the watch case, looks very much like any other watch band, and feels quite comfortable to me. Additionally, the distance between two consecutive holes for band length adjustment is about 5 mm. That allows for quite a bit of tension adjustment, and overall, for the types of physical activities I perform, works well for me. I don’t always wear it when sleeping. I can also see how some people would like to have a possibility for finer adjustment. If you are looking to change bands on your fēnix® 3 HR, keep in mind the optical sensor accuracy could be affected depending on the specs of the new band you choose.

The pins of the fēnix® 3 HR watch band are more robust than the usual watch band pin. But they are not as thick as the pins on the epix™ (pictured on the left, on the photo below). For reference, a bike chain pin is placed in between the bands.

But a chain is just as strong as its weakest link so those two pins on the case wouldn’t help if the pin holding the buckle didn’t match them in strength. In the case of the fēnix® 3 HR, all three pins composing the band seem to be of similar construction.

Other dimensions and weights all seemed to match values listed online and I didn’t find anything unusual or unexpected.

“Unpacking”

Now let’s turn off all watches and take a good look inside. Although I describe the steps I performed, this article should not be used as disassembly instructions. The first step is to remove the five screws that fix the bezel to the case.

I worked those out in a star pattern.

Then I just had to pry the bezel away from the rear case to get my first glimpse at the internals of the fēnix® 3 HR.

There was a flat cable connecting the display to the motherboard.

That cable connector comes off easily from the motherboard by gently pushing it away from the board with a small dull tool, one side at a time, and back again, until it pops.

The red sealing gasket came off with the bezel. But the easiest way to put it back when closing the watch is to actually position it on the rear case.

Back to the watch case, the top piece is the GPS antenna, or part of it. The GPS antenna is described as an omni-directional stainless steel EXO™ antenna, suggesting electromagnetic coupling with the external, PVD-stainless steel bezel. But stainless steel is a relatively poor conductor of electricity, with lower electrical conductivity than copper. So perhaps the particulars of the PVD process used also play a role. The internal piece comes off easily without removing any other screws, as the electronic connection is made through the three prongs seen on the top right of the motherboard.

There are however two screws now holding the motherboard to the rear plastic case. Those need to be removed before we can continue.

That allows for the motherboard to be turned over gently, as it is still connected to the case via a second flat cable. The hidden side of the optical sensor is then revealed for the first time. The flat cable connects the motherboard to the optical sensor that is located on the bottom of the case, being that the distinctive difference with respect to its predecessor: the fēnix® 3. This side of the motherboard also shows that the vibration motor is connected to the motherboard (instead of being fixed to the case, like it is on the epix™ or on the Smart Run, for example) and the specs printed on the battery were slightly different than what I was expecting, overall reminding me of the general impressions I got from the Moto360.

I carefully removed a small piece of tape that seemed to have been placed so to further secure the connection of the optical sensor’s flat cable to the motherboard.

After the tape was removed, I just had to gently push the connector away from the board for it to pop up.

And there you have the case and the motherboard disconnected from each other.

Before we continue with the motherboard, let’s inspect the rear case. It is made of ultra-strong, glass fiber reinforced plastic, and provides housing for the electronics.

Besides the optical sensor, the barometer is also situated in a small cylindrical compartment, seen on the right in the photo above. But as I was making my way to the little barometer, I found the mechanical buttons pretty interesting. Like the bezel, they are also PVD-stainless steel, and all colors match very nicely.

I slightly moved the small metal piece that holds the ‘Down’ button in place.

And as I totally removed it from its place, I was able to slide the button off its hole, along with a spring.

I would be interested in customizing the appearance of the mechanical buttons on my watches.

Now back to the barometer. It is secured in place in its compartment by a small plastic piece that is screwed to the case. It also makes an electronic connection to the motherboard via three prongs. Barometers need to take into account their operating temperature in order to improve the accuracy of air pressure measurements. A metal spring functions as a probe for the embedded thermometer.

The barometer has a very small o-ring for preventing water leak through its compartment and into the watch. When assembling it back, the little nozzle simply slides inside the cylindrical compartment, creating a very nice seal.

Now back to the motherboard. On one side, the battery seems to be connected to it by a strong adhesive. It didn’t look to me like there was anything to be learned by separating it from the motherboard, so I left it in place (and its cable always connected and powering the motherboard).

On the other side of the motherboard, we can see the typical metal plate commonly used to house important chipsets, shielding them from electromagnetic interference coming from the Bluetooth®/ANT ® radio communications. It also contains a really tiny speaker, which looks like just an extra circular plate of a different material built into the metal shield.

After the metal shield is removed, the most important chipsets are finally visible.

Conclusion

No fēnixes were harmed during this teardown. A watch teardown often entails destroying it. But that is so, often because there is no other choice. It is the only way for the more curious end-users to get a chance to inspect watch’s internals, once they reach their end of life, and are ready to be recycled anyway. Since I just purchased my fēnix® 3 HR, from the start it was an important goal for me to be able to not only put the watch back together again, but for it to then be fully functional. Think of it as disassembling a PC to do an upgrade. All went well and I have already used it for all the functions it was designed to provide, including several long pool swims. That really speaks to how solid, robust, and well engineered this watch is, inside and out. It is as rugged and tough inside as it is on the outside. That fact alone made me pretty happy as an end-user, and even more proud of it as an owner. It also makes me hopeful that some day we will indeed be able to swap out internals of our watches as we see fit. The most challenging step for me when taking the watch apart was to remove the metal shield. It holds the speaker so it would be nice to be able to replace it more easily. I also think the ability to replace and upgrade the Li-Ion battery at home would be awesome. The most challenging step when putting it all back together again was to plug the connector for the optical sensor back and tape it in place. I was stubborn, didn’t want to use magnifying glasses for that, and the flat cable kept getting in my way. But ultimately I succeed! It did however remind me of the first time I had to plug a VESA video board on a PC motherboard, one of my dearest childhood memories, relived again via a 6-pin, millimetric connector. Good, pre-PCI bus times.