Finding accelerometer location inside a phone

[Haversin]

I'm off by 7mm in my measurement. Meaning I would have soldered out the wrong chip  

Fantastic work Physikator ! 
I'm still looking for images of my motherboard so I can do the same error measurement.

[Haversin]

I found two good images of my phone's logic board on ebay. The positioning of the logic board inside the phone was estimated from a teardown video. The rear side of the board with all six accelerometer position estimates plotted to scale are shown here.
   
Only three of the positions were on the logic board and only two of those landed on a chip. The IMU chip used on my phone is a LSM6DSL. The data sheet for the LSM6DSL gives it's size as 2.5 mm by 3.0 mm by 0.8 mm. This matches the size of the chip that the accelerometer minus bias position estimates fell on. I'm fairly confident that this is the accelerometer/gyro chip. The front side of logic board is shown below with the three positions estimates that landed on the board. None of these positions landed on a chip for this side of the board.
   

[Physikator]

That also looks pretty convincing! I'm still looking for a decent turntable.

I tried using a cordless screwdriver with an adapter for a grinding disk and some velcro to generate the rotation. The result is horrible because the thing accelerates and decelarates rather promptly. And (theoretically) not knowing where the accelerometer sits you have to use the absolute value of the acceleration. The various circle do not cross in a single point, but only within 10mm.

[solid]

Very interesting! Precise location of the accelerometer in a smartphone is very important for correct measurements using it. To the information given here and many other places I would like to add a reference:
Sidney Mau, et al. Locating a smartphone’s accelerometer. Physics Teacher, vol.54, p. 247 (2016); doi: 10.1119/1.4944372

[solid]

Two more references for this important subject:

1.  Christopher Isaac Larnder, and Brian Larade
   "On the determination of accelerometer positions within host devices,"
   American Journal of Physics 87, 130 (2019); https://doi.org/10.1119/1.5082536
   
2. Chris Isaac Larnder
   "A Purely Geometrical Method of Locating a Smartphone Accelerometer,"
   The Physics Teacher 58, 52 (2020); https://doi.org/10.1119/1.5141974