What to check when buying a used phone Xiaomi: the complete guide

The used electronics market in Russia is growing at leaps and bounds, and Xiaomi devices occupy a significant share there. It is logical: for relatively little money you can get a device with top-end hardware, which is still relevant. However, it is the popularity of the brand that attracts many scammers and sellers who hide the real defects of the gadget. Buying a smartphone from hand is always a lottery, where the winnings depend on your attention and technical knowledge.

Many customers make the same mistake: they only check the appearance and ability to call, which is categorically not enough for modern sophisticated technology. Hidden problems such as a restored IMEI, a tired power controller or a glued display of poor quality can surface a week after purchase. To avoid turning a bargain into an expensive “brick”, you need to conduct a deep diagnosis right when you meet the seller.

In this article, we're going to look at a step-by-step algorithm that will weed out 90 percent of the problem devices, and we're not going to rely on "maybe" but on engineering menus, special codes, and visual magnification, and remember that a salesperson who has nothing to hide will be comfortable with your meticulous check.

External inspection of the body and display

Starting a used Xiaomi phone with a thorough visual inspection in good lighting is always a red flag, looking for chips, deep scratches and scuffs, especially in the corners of the case. The presence of autopsy marks, such as broken seals on the screws or unnaturally wide gaps between the frame and the screen, which may mean that the phone was opened for poor repair or replacement of the battery with a cheap counterpart.

Pay special attention to the screen. Turn on the white picture at maximum brightness and carefully examine the matrix. On the AMOLED panels that are equipped with many Redmi and Poco models, the blue subpixel often burns out, which leads to a pink hue. Also check the touchscreen for dead zones and plume detachments, which can manifest as stripes or improper multi-touch operation.

• 🔍 Take a close look at the charging connector USB Type-C: inside should not be oxides, blackness or loose tongue.
• 🔍 Check the tray. SIM-maps: it should sit tight, without backlashes, and the map itself should be determined instantly.
• 🔍 Examine the camera: there should be no dust or condensate under the protective glass, which indicates a violation of the tightness of the body.

If you notice that the phone's frame has paint marks in places where they shouldn't be (like inside the speaker connector), it's a sure sign of artisanal repainting. These devices are often recovered from broken donors, and their reliability is a big question.

Diagnostics of the screen and touch layer

After an external inspection, you need to go to the software check of the display. In the shell of MIUI and its successor HyperOS, there is a built-in engineering menu that allows you to conduct a rapid test of all components. To start the diagnosis, enter the code ##6484## in the Phone application. If the code does not work, try ##4636# or go through Settings → About Phone → MIUI version (you need to quickly press 10 times, but this does not work on all versions).

In the CIT (Customer Inspection Test) menu, select the item associated with the display check (usually "Display" or "Touch"), and you will be asked to swipe across the screen to make sure there are no gaps in the grid coordinates, which is a critical step, since even the slightest defect in the plume can cause the phone to stop responding to touch in a certain area after a month.

⚠️ Note: If the seller claims that the screen has been changed, but the engineering menu color test shows uneven backlight or "lights" on the edges, then a cheap copy of the low-quality matrix is installed.

Also check the proximity sensor. During the test, hold your finger to the top of the screen to go out and light up. A faulty proximity sensor is a common problem after poor repairs, which can cause the phone to turn on the speaker itself during a conversation or not turn off the screen in your pocket.

Checking the battery and charging system

Battery status is one of the main parameters when buying a used smartphone. Lithium-ion batteries degrade over time, and even if the phone "holds charge" according to the seller, the actual capacity can be significantly lower than stated. In the CIT engineering menu, select "Battery" or "Battery Indicator" to see the current status and voltage.

Pay attention to the behavior of the smartphone while charging. Connect the original (or quality certified) power supply. If the phone does not start quick charging (Quick Charge or Power Delivery), although it used to work, the problem may be in the power controller or the connector itself.

For a more accurate estimate, you can use third-party utilities if you can install them, or just watch the percentage of charge. A sharp jump, for example, from 40% immediately to 15% or turn off the phone at 20% charge, indicate the degradation of the battery cells and the need to replace it.

• 🔋 Check if the battery is swelling: put the phone on a flat surface and try to spin it - it should not rotate like a yule.
• 🔋 Make sure the cable does not move away with light movement in the connector.
• 🔋 Za. 5-10 The charge should not fall more than a minute. 10-12%.

Device authentication and IMEI verification

One of the riskiest things is to buy a stolen or refurbished phone to avoid police problems or lockdowns. IMEI, You need to check the identifiers. Type *#06# and compare the displayed code. IMEI with the number on the box (if any) and on the sticker in the tray SIM-All three values must match perfectly.

Next, check the phone by official databases. For Xiaomi devices, it is important to check the status of the Mi Account binding. If the previous owner did not log out of his account and did not delete the device from the trusted list, you will get a locked device after the reset. Make sure that there is no other person’s data in the Settings → Mi Account section, and the status of the device is “Activated” (or the device does not appear in the list of others).

Also check for FRP (Factory Reset Protection) locking.This is Google protection, which requires you to enter a password from an account that was synced to the phone before the reset. If the seller offers to reset the phone in front of you, make sure that after turning it on, they don't ask for someone else's Google account.

Testing of cameras, sound and communication modules

Multimedia is what we love about smartphones. Start by focusing your camera: point your lens at close range, then at a distant object. Autofocus should be fast and clear. Take some pictures in good light and low light — you shouldn't have black spots (dust on the matrix) or purple stripes.

The sound system is tested in a complex way. Turn on the music at maximum volume through the speaker — there should be no wheezing or rattling. Then make a test call: check the main microphone, the bottom (noise reduction) and the speaker in the ear. If the person hears you poorly or the sound is "floating", it is possible that the microphone holes are jammed or the plume is damaged.

⚠️ Warning: If the app crashes when the camera is turned on or a black screen with the words "Cannot connect to camera" appears, this is a sign of a hardware malfunction of the module or plume, often occurring after a fall.

Don't forget to check the wireless modules. Connect to the Wi-Fi network and try to download a large file. Turn on Bluetooth and try to transfer the file to another phone. Lack of GPS signal or its very poor quality (if you're not in the basement) can indicate a severed antenna contact inside the housing.

Checking for flooding and hidden defects

Water is the main enemy of electronics, and the traces of contact with liquid may not appear immediately. SIM-card or near the charging connector is often a humidity indicator (LCI). It's normally white or silver, and if it's bright pink or red, it's got a precise contact with water.

Even if the indicator didn't work, smell the charging connector and speaker, smell damp, mold or vice versa, the sharp smell of chemistry (an attempt to wash in ultrasound) should alert you. oxidation of contacts can begin a week after purchase, killing the motherboard.

• 💧 Examine the cameras: inside the lenses should not be condensate or drops.
• 💧 Check the speakers: the sound should be clean, without the effect of "gurgling".
• 💧 Put the flashlight on. 2-3 minutes: if the phone starts to warm unevenly or the screen starts to blink, problems with the power chains may occur.

It's also worth checking the vibrator, and it should vibrate smoothly, without cracking or jamming, and when you're running the vibrato, you might be able to see that there's dust or moisture going into the machine.

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Use AIDA64 or CPU-Z to view detailed hardware information, and these utilities will show the actual CPU model, screen type, and battery wear, which will help identify broken performance in fake devices.

Unlocking the bootloader and device status

For advanced users, Bootloader status is important. If you plan to install custom firmware, you need an unlocked bootloader. However, if the phone is bought for normal use, having an unlocked bootloader can be a downside: some banking applications stop working and data security is reduced.

You can check the status by holding down the Volume Down + Power buttons at the same time when the phone is turned off. The Fastboot logo and the hare in the header will appear on the screen. The status bar will say Locked (locked) or Unlocked (unlocked). If the bootloader is unlocked, check with the seller the reason - perhaps the phone was used for mining or tests, which reduces the memory resource.

Also check if the phone is blacklisted, especially for devices imported from abroad, but you can check IMEI on the websites of major carriers or through specialized verification services.

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Buying a phone with an unlocked bootloader (Unlocked) is only justified if you are enthusiastic and understand the risks.For the average user, Locked status is safer and more stable.

Frequently Asked Questions (FAQ)