Approximate sensor on Xiaomi Poco X3 NFC: Where to find out how to check and replace

Approximation sensor in Xiaomi Poco X3 NFC — A small but critical component that automatically shuts down the screen during phone calls, so when you hold the device to your ear, the sensor detects the obstacle and extinguishes the backlight, preventing accidental tapping and saving battery life. However, over time, this module can fail: the screen does not turn off when calling, reacts with a delay or, conversely, goes out for no reason.

If you're facing problems like this, the first thing you need to do is check the physical condition of the sensor, but where exactly is it in the Poco case. X3 NFC? Unlike flagship models, where sensors are often integrated into a display module, the sensor is made separately in this device, its position is not obvious to most users, especially if you have not previously had to disassemble a smartphone. In this article, we will show the exact location of the sensor on the board and in the case, and also explain how to diagnose its operation without disassembling the device.

Design of the proximity sensor in Poco X3 NFC: technicality

At Xiaomi Poco X3 NFC Infrared approximation sensor of the model STK3338 (or its equivalent, which consists of two key elements:

• 🔦 Infrared LED (IR LED) — lights out.
• 👁️ Photodiode – captures the signal reflected from the obstacle.

When you hold the phone to your ear, the infrared beam bounces off the surface and goes back to the photodiode. The microcontroller analyzes the strength of the signal and sends a command to turn off the screen. X3 NFC The sensor works in tandem with the light sensor, which is also located nearby – this often causes confusion in the diagnosis.

The thing about the model is that the sensor is not soldered into the motherboard, but is connected through a flexible plume, which makes it easier to replace it, but makes it more vulnerable to mechanical damage, for example, if a phone falls, the plume can detach or break, which will lead to incorrect operation of the sensor.

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If the sensor stopped working after replacing the screen, check the integrity of the plume - it could be damaged during disassembly.

Where exactly is the proximity sensor: diagrams and photos

At Xiaomi Poco X3 NFC The proximity sensor is located at the top of the device, next to the speaker of the conversational type. If you look at the front of the phone, the sensor is located in the front of the phone:

• 📱 Left of the front camera (under the protective glass).
• 🔍 Under the decorative grid speaker - visually it is not visible, but it is hidden under a plastic grille.
• 🛠️ On the back of the display module – when disassembled, it can be seen as a small black rectangle (3×2 mm) with two contacts.

On the motherboard, the sensor is connected via a connector. CN201 (the marking may differ depending on the audit of the fee. Below is a layout scheme:

To identify the sensor accurately, look at the back of the display module after the screen is removed, and the sensor will be glued to a metal frame next to the plume connector. X3 NFC The sensor can be marked with white paint or an inscription PROX.

Signs of malfunction of the proximity sensor

If the proximity sensor starts to fail, it will manifest in one or more symptoms:

• 📵 The screen does not go out during the call, even when the phone is pressed to the ear.
• 🔄 The screen is spontaneously turned on/off for no reason.
• ⏳ Reaction delay – the screen goes out 2-3 seconds after the phone is lifted.
• 🔇 Automatic volume control does not work (if the light sensor is also defective).
• 📱 The sensor does not respond in test applications (e.g. #6484##).

Most often, problems arise due to:

1. Sensor contamination – dust or fat blocks the infrared signal.
2. Damage to the plume - an overbending or break of contacts.
3. Firmware failure - errors in the operation of the sensor driver.
4. Mechanical impact - the displacement of the sensor relative to the body.

Before you disassemble the phone, try a software diagnostics.

1. Open the Phone app and dial ##6484##.
2. Select the Proximity Sensor.
3. Close the sensor with your finger – the value should change from 5 (no obstacle) to 0 (there is an obstacle).

⚠️ Warning: If the sensor doesn't respond in the test menu, but it's physically intact, the problem may be in the firmware. Try resetting to factory settings or reflashing the device via Fastboot.

How to check the sensor without disassembling the phone

Before you take down Poco X3 NFC, Try diagnosing the proximity sensor without opening the body:

1. Verification through the engineering menu

The most reliable method is to use the hidden menu of Xiaomi:

1. Open the Phone app.
2. Enter the combination ##6484## (some firmware may not work, then use ##4636###).
3. Select Proximity Sensor.
4. Put your hand to the top of the screen, and the value should change from 5 to 0.

2. Testing with the help of applications

If the engineering menu is not available, install one of the applications:

• 📱 Phone Tester – Shows the status of all sensors.
• 🔍 Sensor Box for Android – Detailed Sensor Information.
• 🛠️ CPU-Z — In the Sensors section, the proximity sensor data is displayed.

3. Visual examination

Take a flashlight and shine it at an angle on the top of the screen, and if the sensor is contaminated, you'll see:

• 🕳️ Dust or dirt under a decorative speaker grille.
• 💧 Traces of fluid (if the phone fell into the water).
• 🔧 Shifting the protective glass – this can block the signal.

⚠️ Warning: If the sensor is responsive in test apps but doesn't work during the call, the problem may be with Android settings. → System system → Gestures → Turn off the screen when you bring it to your ear.

Step-by-step: how to get to the proximity sensor

If the software doesn't work, you'll have to take the phone apart.

• 🔧 Plastic blades (to open the body).
• 🔨 Cross screwdriver (for screws) T3 or T4).
• 🧲 Magnetic mat (so as not to lose the screws).
• 🔥 Hair dryer or thermo-air station (to unplug the screen).

Sequence of action:

Step 1: Removing the back cover

1. Turn off the phone and remove the SIM- card.

2. heat the tail dryer edge of the back cover (temperature) ~60°C).

3. Carefully tuck a plastic spatula from the lower corner and lead along the body.

Step 2: Battery disconnection

1 Unscrew 4 screws that fix the metal plate of the battery.

2. disconnect the battery connector (use a plastic blade to avoid damaging the contacts).

Step 3: Removal of the display module

1. Heat the screen around the perimeter (especially in the upper part where the sensor is located).

2. Tuck the display and gently lift it. Be careful - the sensor plume is very fragile!

3. disconnect the sensor plume connector (marking) CN201).

Step 4: Access to the sensor

1. On the back of the display module, you'll see a black rectangle -- that's the proximity sensor.

2. It's glued to a frame - gently tuck it in with a plastic spatula.

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Don't pull the sensor plume, it breaks easily, and you'd better gently stick it on the side.

If the sensor is damaged, it can be replaced with a new one (article: Xiaomi Poco) X3 NFC Proximity Sensor Flex Cable: Average cost of a spare part is 300-500 rubles.

Frequent errors when replacing the proximity sensor

Even experienced craftsmen sometimes make mistakes that lead to repeated failures.

• 🔥 Overheating the screen - temperature above 70°C may damage glue and plumes.
• 🔪 Using metal tools to tweak the sensor - this leads to circuits.
• 💦 Drain alcohol on the plume - it corrodes the insulation of conductors.
• 🔌 Connecting the battery to full assembly - the risk of short circuit.

Typical problems after replacement:

⚠️ Warning: If the screen reacts to late touch after the sensor is replaced, you may have damaged the touch layer plume, and you will need to replace the entire display module.

Alternative ways to solve the problem

If the proximity sensor is out of order, but you do not want to disassemble the phone, try these methods:

1.Switching off the sensor programmatically

You can completely deactivate the sensor through ADB:

adb shell settings put global proximity_sensor_disabled 1

After that, the screen will not go out during calls, but you can use the phone without disassembly.

2. Use of third-party applications

Install Proximity Sensor Fix from Google Play. The app emulates the sensor's operation, but requires root rights.

Calibration of the sensor

Sometimes resetting calibration helps:

1. Enter the phone application ##6484##.
2. Select Proximity Sensor Calibration.
3. Follow the instructions on the screen.

FAQ: Frequent questions about the proximity sensor in Poco X3 NFC