Teardown: Failed MovNow W79 (Counterfeit Xiaomi) Fitness Tracker

Someone had commented on my review of the MovNow W79 about that to do about his fitness tracker which suddenly stopped working. An interesting coincidence? Mine also stopped working for some unknown reason.

I tried my best to revive it – different USB ports, applying pressure to the unit, trying to push it deeper in the charger, giving it a few days rest and trying to charge again. Nothing seemed to change its mind – no LED indications came up, and under BLE scanners, it didn’t turn up anymore.

I decided it was dead, and a total lost cause. I was sick of it, and much preferred the Xiaomi (genuine of course), which I use from day to day. As a result, I decided that there was no point in keeping it or trying to revive it, so I decided to take it apart.



Opening this unit up was no drama at all. In fact, I was surprised that it was even considered waterproof given that the only form of seal was a glue seal around the edge that was easily defeated with a flick of a flat-bladed screwdriver. There really isn’t much inside – the base has the two charging pins, the lid has holes for the LEDs to shine through, and the rest of the unit is on one PCB.


Getting out the macro lens for a closer look, we can see that there is a chip antenna at the far left, and the Bluetooth Low-Energy chipset (DA14580) from Dialog Semiconductor. Near that is a 16Mhz clock crystal, and a transistor, which probably controls the vibrator module. Below that is an ST Microelectronics chip marked 8427 C3H O4WA9 which I presume is a LIS3DH digital MEMS motion sensor. There is another chip marked 5F2 A4A J0G, which may be power management/battery charge control/LED drive related. A six-pinned IC is also visible near the power input, which may be the actual charge controller or just a simple MOSFET.


The rear has the Li-Poly battery and the vibrator unit mounted by self-adhesive tape.


The battery claims to be a 30mAh cell made in November 2014. It has its own cell protection board.


The rear of the PCB is marked BW79_V1.0 and is dated 25th October 2014 and doesn’t have any components.


In such a small space, there really isn’t much possibility for fitting in a large number of components. Indeed, what we’ve come to find is exactly what we expect. I was surprised that such a poor physical case could be considered waterproof given the ease of opening. Its failure may have been due to an over-discharged battery or a failure somewhere in regards to battery charge control. As I haven’t the time to hack around with it, I cut my losses, tore it apart and threw it out.

If you are having problems with your unit – try giving it a break for a week and then try charging it again in case it has hung. Try applying pressure on the unit in the charging socket, and clean the pins. If not, see if you can find it on a Bluetooth Low Energy scanning app. If all else fails … maybe it’s time for a new one … and maybe a genuine Xiaomi from a more reputable vendor this time.

About lui_gough

I'm a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!
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