Open compass and turn iPhone. The pointer does not move.

First we measure whether the power supply of compass control chip is normal. Through circuit diagram, we know that compass control chip U1901 requires the power supply from PP3V0_IMU and PP1V8_OSCAR, as shown in picture 4-56.

Through PCB bitmap, we know that the power supply of PP3V0_IMU and PP1V8_OSCAR can be measured at C1902 and C1901 near U1901, as shown in picture 4-57. The material object of capacitors C1902 and C1901 is shown in picture 4-58. Energizing iPhone, measure the voltages and they are normal. Replace the compass control chip and measure again. The problem is still the same.

Measure the diode data to ground of four circuits of SPI bus that communicates with compass control chip. With the normal power supply and bus and the replaced chip, we presume that other components cause the problem. Checking the circuit diagram again, we find that SPI bus connects co-processor U2201, gyroscope chip U2203, baroceptor U2204 and accelerator U2205, as shown in picture 4-59~62.

Through schematic diagram, we know that any of the four chips on SPI bus, the other three chips will be affected through SPI bus. Open compass and turn iPhone. The pointer does not move, as shown in picture 4-63.

Turn off iPhone and replace gyroscope chip U2203. The material object of U2203 is shown in picture 4-64.

Then assemble iPhone and get into IOS to test. Gyroscope and compass function recovers. Trouble is removed.