The problem with the screen going out during a call on the Xiaomi Redmi Note 9 is one of the most common complaints of users of this model: you call, you hold the phone to your ear, and suddenly the display goes out, leaving you in the dark whether the conversation is still going, or the connection is interrupted. In some cases, the screen does not respond to touch, and you can only bring it back to life after the call is completed or the device is rebooted.
The reasons for this behavior can be both software (firmware failures, sensor errors) and hardware ( plume damage, sensor contamination). In this article, we will analyze all possible scenarios, from trivial settings to serious breakdowns, as well as give step-by-step instructions for diagnosing and troubleshooting, and pay special attention to the nuances specific to the Redmi Note 9 (codename merlin), including problems with the STK3338 proximity sensor and conflicts with the MIUI shell.
If you've tried to reboot your phone or reset your settings, but the problem is, don't rush to bring your device to service, 80 percent of the time you can do it yourself, following our recommendations, and for those who are ready for a more in-depth repair, we've prepared a detailed guide to disassembling and inspecting hardware components.
1. Approximation sensor: the main cause of the screen that went out
In 90% of cases, the proximity sensor, a small sensor next to the front camera that detects when you hold your phone to your ear, is to blame. The Redmi Note 9 uses the STK3338 sensor, which often fails due to contamination, damage or software errors.
How does it work? When you call and hold the phone to your head, the sensor picks up the obstacle and sends a signal to the system to turn off the screen (to avoid accidental taps). If the sensor is faulty, it may falsely fire or, conversely, not respond at all, as a result of which the screen goes out at the wrong time or does not turn back on.
- 🔍 Signs of sensor malfunction: the screen goes out immediately after the start of the call, does not turn on when the phone is taken away from the ear, reacts with a delay.
- 🛠️ How to check: Call your phone and swipe your hand over the top of the screen (where the front camera is located.
- ⚡ Quick solution: Turn off the sensor function in the settings (temporarily) to check if it is the case.
On the Redmi Note 9, the proximity sensor often suffers from dust or moisture under the protective glass, and if you've recently dropped your phone or used it in the rain, there's a high risk that the sensor is contaminated, in which case a careful cleaning or replacement of the sensor will help.
What does the proximity sensor look like on the Redmi Note 9?
2. Software failures: MIUI, firmware, and application conflicts
Xiaomi's MIUI shell is known for its features, which sometimes work incorrectly, one of which is to control the screen while you're calling, and if the proximity sensor is fine but the problem persists, it could be:
- 📱 Failures in MIUI: Errors in recent updates (especially relevant for versions) MIUI 12.5 and MIUI 13).
- 🔄 Application conflicts: Some programs (such as launchers or optimizers) may block the sensor from working.
- 📲 Incorrect settings: the call menu can activate the function "Switch off the screen when approaching", which works unstablely.
The first thing you need to do is to restart your phone in safe mode, and that will turn off all third-party apps, and you can see if the software is to blame.
- Press the power button before the off menu appears.
- Press and hold the "Switch off" option (a suggestion will appear to go to safe mode).
- Check and verify if the problem is recurring.
If the screen doesn't go out in safe mode, it's one of the apps you installed. Try to remember which programs you installed before the problem occurred, and delete them.
- 🎵 Music players with the function of "smart call management".
- 🔒 Apps to lock screen or save battery.
- 📞 Alternative calls (such as Truecaller or Drupe).
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Before you delete your apps, check their permissions in Settings → Apps → Permissions. If the program has access to your phone or sensors, it can affect screen performance.
3. Phone Settings: What Can Be Changed Without Repair
Before you disassemble the phone or drop it to factory settings, check a few key parameters. Often, the problem is solved in just two clicks.
Disabling the proximity sensor during the call:
- Open the phone app.
- Click on the three dots in the top right corner and select Settings.
- Go to Call Settings. → Additionally.
- Find the item "Switch off the screen when approaching" and turn it off.
If the screen stops going out after that, the problem is the sensor, so you can leave that function off (minus, the screen won't lock when you talk) or repair the sensor.
Reset sensor settings:
MIUI has a hidden menu for calibrating sensors.
- Open the phone app.
- Enter the code ##6484## (some firmware may not work).
- If the menu is open, select Proximity Sensor and calibrate.
If the code doesn’t work, try an alternative method through the engineering menu:
- Enter ##4636##.
- Go to the phone information.
- Scroll down to the Sensors block and check the Proximity sensor readings.
Turn off "Switch off the screen when approaching"
Check the operation of the sensor in the engineering menu
Remove suspicious applications
Update MIUI to the latest version
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Hardware malfunctions: from plume to battery
If the software methods didn't work, the problem is probably the hardware.
| Component | Signs of malfunction | How to check | Cost of repair (approximately) |
|---|---|---|---|
| Display plume | The screen flickers, goes out when the phone is tilted, artifacts appear | Shake the phone – if the image is distorted, the plume is damaged | 800–1500 ₽ |
| Approximation sensor | The screen goes out immediately when you call, does not respond to the withdrawal of the phone | Call the multimeter or replace it with a knowingly working | 500–1200 ₽ |
| Battery | The phone turns off at low charge, the screen goes out when loaded | Testing with a voltmeter or replacing it with a new battery | 1000–1800 ₽ |
| Display contact | The screen periodically turns off, reacts to pressing the body | Disassemble the phone and check the density of the plume | 300–800 ₽ (purification) |
The most common hardware problem is damage to the display plume. On the Redmi Note 9, it is often rubbed at the bend, especially if the phone is dropped or bent, and the screen can work normally but go out when you call due to the increased load on the GPU.
How to check the plume:
- 🔧 Carefully press the bottom of the screen (where the plume connects to the motherboard). If the image is distorted, the plume is damaged.
- 📱 Check if there are no stripes or flickering on the screen when tilting the phone.
If you're not afraid to take your phone apart, you can try reconnecting the plume yourself, and you'll need a plastic blade and a hair dryer (to soften the glue). On the Redmi Note 9, the plume is not only latched, but also glue--be careful not to tear it when it's disconnected.
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If the screen goes out only when you call, and the rest of the time it works normally, there's a 95% chance that the proximity sensor or its plume is a problem, and the display plume usually crashes all the time, not in specific scenarios.
5. Update firmware and reset settings
If the problem occurred after the MIUI update, there is a good chance that the firmware is to blame. Xiaomi often releases updates with bugs that the later fixes in the following versions. Redmi Note 9 is known for firmware problems:
- MIUI 12.0.8.0 – Massive complaints about the proximity sensor.
- MIUI 12.5.1.0 – The screen goes out when you call via Bluetooth headphones.
- MIUI 13.0.4.0 – conflict with Google Phone (default caller).
How to update the firmware correctly:
- Go to Settings → About the phone → System update.
- If a new version is available, upgrade. If not, click on the three dots in the upper right corner and select "Update Package".
- Download the latest stable firmware from Xiaomi’s official website (e.g. MIUI 14 for Redmi Note 9) and install it manually.
If the update didn’t work, try resetting to factory settings:
- Make a backup copy of the data (photos, contacts, messages).
- Go to Settings → Additional → Recovery and Reset.
- Select "Resetting" and confirm.
⚠️ Warning: After the reset, all data will be deleted, including accounts and apps. If you have a Mi Account linked, be sure to unplug it before the reset, otherwise the phone may be blocked.
6.Alternative solutions: from launchers to magnetic covers
If standard methods don't work, try non-obvious ways. Sometimes the problem is in the little things that users don't know.
- 📱 Launcher Change: Some shells (like Nova Launcher or Apex Launcher) conflict with system services MIUI. Try to return the standard launcher.
- 🧲 Magnetic cases: If you use a magnet case, it can affect the Hall sensor (responsible for closing the case) and indirectly the proximity sensor.
- 🔋 Power saving mode: In battery settings (Settings) → Battery → Power saving mode, you can activate an option that limits the sensors.
- 🎧 Bluetooth devices: If the screen only goes out when the headphones are connected, try turning them off or resetting your Bluetooth settings.
Extreme method: If nothing works, you can try installing custom firmware (like LineageOS or Pixel Experience). This is a radical solution, but it often saves you from MIUI bugs.
- Unlock the bootloader (bootloader).
- Install TWRP Recovery.
- Sweep through the alternative firmware.
⚠️ Warning: Installing custom firmware will void warranty and may lead to a phone breeze if you do something wrong.Do this only if you are confident in your abilities or under the guidance of an experienced user.
7. When is the time to bring the phone to service
If you've tried all the methods, but the screen still goes out when you call, it's probably a hardware problem.
- 🔧 The phone fell or was exposed to moisture.
- 📱 The screen flickers or artifacts appear (stripes, dots).
- ⚡ The problem is accompanied by spontaneous reboots.
- 🔋 The battery is quickly discharged or the phone turns off when the charge is low.
What to say to the master:
Describe the problem in as much detail as possible:
- When it appeared (after a drop, update, install the application).
- How the screen behaves (it goes out immediately, after a few seconds, does not turn back on).
- What you have tried to do (reset, update, check the sensor).
Average cost of repair in the service:
- Replacement of the proximity sensor: 500–1200 ₽.
- Replacement of the display plume: 800–1500 ₽.
- Diagnostics + cleaning contacts: 300-600 ₽.
If the phone is warranty, do not disassemble it yourself - this will void warranty obligations.
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Before visiting the service, make a backup copy of the data. In some cases, a complete reset of the phone is required for repair.