Buying a smartphone from hand is always a lottery, where the winner is the flagship model at the price of the budgetary, and the loser is the “brick” with a lot of hidden problems. The used electronics market is full of offers, and among them there are often devices that have been repaired, drowned or even stolen. Xiaomi, as one of the most popular brands, is especially often featured in sales ads, which attracts fraudsters and unscrupulous sellers. Careful diagnosis of the device before transferring money is the only way to protect yourself from disappointment.
Many customers make the mistake of just checking the phone and checking the phone, but modern technology allows them to hide serious defects, change the phone. IMEI-You need to know the specific engineering codes and the operating system to avoid becoming the owner of a problem gadget. MIUI In this article, we will discuss a step-by-step algorithm of actions that will help you to identify even those problems that the seller tried to hide.
You don't have to rely on the honesty of the seller, because they may not know all the details of their device, especially if you bought it in the same way. Xiaomi has a rich testing functionality that you need to be able to use. We'll look at both software methods for checking through hidden menus and physical inspection of components so you can get a full picture of the state of the gadget.
External inspection and inspection of the hull for repair
You should start familiarizing yourself with the device well before the screen is turned on. Carefully inspect the case in good light, preferably using the flashlight of another phone. Pay attention to the joints between the frame and the screen, as well as the back cover. If the gaps are irregular, there are protrusions or traces of glue, this is a sure sign of opening the case or poor replacement of parts. Xiaomi factory assembly is very accurate, and the "walking" gaps are unusual for it.
Pay special attention to the screws near the charging socket and speaker. Often, this is where the screwdriver marks in the form of a broken thread or scratches on the screw hats remain. This may indicate that the device was opened to replace the battery or repair the board. SIM-maps: it should open smoothly and its color should match perfectly with the color of the frame of the body.
⚠️ Warning: If you notice a greenish or whitish stain inside ports (chargers, headphones) or on contacts SIM-This is a sign of oxidation after contact with water. Even if the phone turns on, corrosion can slowly destroy the board, leading to sudden failures.
Check the volume and on buttons. Press them in turn: the stroke should be clear, without jamming, and the click should be audible and elastic. Shattered or soft buttons often indicate internal wear or fall effects. Shake the phone next to the ear: there should be nothing rattling inside. Having a foreign knock can mean the camera module, battery or just dust and dirt that gets inside, which is critical for tightness.
Diagnostics of the display and sensor through the engineering menu
The screen is the most expensive and fragile part of a smartphone. It's not enough to just look at the picture, you need to check the uniformity of the backlight and the touchscreen. To do this, Xiaomi has a built-in engineering menu. Open the Phone app and type in the code ##6484##. If the menu doesn’t open, try the code ##4636## or check in the About Phone settings – you need to click on the version several times. MIUI, to activate advanced options, although standard CIT-Menu is usually available by default.
In the menu that opens, select the item associated with the display testing (usually called Display or Touch). The screen will be filled with a monochromatic color. Look closely at the white background: it clearly shows “broken” pixels, spots (“clouding”) or uneven backlighting around the edges. By switching colors (red, green, blue), you can identify problems with color reproduction. AMOLED screens, which are on most Xiaomi models, also characterized by burnout of pixels over time, which manifests in the form of dull power of white backgrounds.
Then we go to the sensor test. In touch screen mode, swipe your finger across the entire screen surface. The line should be continuous, without breaks or jumps. Pay special attention to the corners and edges, which are the most common problems with the detachment of the plume. Also check the multi-touch: try to pinch several points at once. If the phone does not respond to all touches or "gluts" when typing is active, this is a bad sign.
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When checking the screen, turn on maximum brightness. Higher values show better matrix defects and uneven backlights, which are invisible in dim light.
Don't forget to check the proximity sensor and autobrightness. There are tests in the engineering menu. Cover the top of the screen with your hand, the screen should go out, and when you move your hand away, it should light up. If the sensor sticks or works over and over, you'll have your screen constantly turning off or not going out during a conversation, which will lead to accidental cheek pressing.
Checking IMEI and status of the device in the Xiaomi database
One of the most important steps is to check that the device is legal. IMEI-code on the box (if any), in the system settings and on the case (if the tray) SIM-The code can be dialed through dialer: *#06#. If the codes do not match or one of them is missing, you either have a machine recovered from different parts or a device with changed identifiers.
Then you need to break through the device on the official Xiaomi database. Go to mi.com/global/verify (or the regional version of the site) and enter IMEI or serial number. The system will show the device model, color and, most importantly, the date of activation and end of the warranty. If the site says that the device is not found, or shows a model different from the one you have in your hands, this is a reason to be alert.
| Status in the database | What does it mean? | Risks. |
|---|---|---|
| Active / In Warranty | The device is active, the warranty is valid | Minimum, phone legal. |
| Out of Warranty | The guarantee is over. | It is normal for the used, but check the date of purchase. |
| Not Found | No database or changed IMEI | High risk of theft or deep flashing |
| Blacklisted | Blacklisted | The phone can be blocked by the operator. |
⚠️ Note: If the seller claims that the phone is a “global version”, but when checking the phone, the IMEI The Chinese model pops up, so the firmware was reflashed from the Chinese version to the global one (CN This often leads to problems with notifications, work. NFC and banking applications, as well as blocking when updating.
You should also check the status of Mi Account. Go to the settings and see if the phone is tied to someone else's account. If the previous owner hasn't untied the device, you won't be able to use it fully, and a factory reset will lock the phone (Mi Cloud Lock). Demand a full logout and reset with you.
Analysis of battery and charging system status
The battery is a consumable, and its condition directly affects the comfort of use. Unlike the iPhone, Android doesn't have a built-in Health feature on the standard menu, but there are ways to find out the approximate condition ##6485##) I can find parameters. MB_06 (battery status; and MF_02 (The number of charging cycles, if supported by the controller. The "Good" value at the status point is the minimum you'll be satisfied with.
Pay attention to charging speeds. Xiaomi is famous for its Quick Charge, Power Delivery, proprietary HyperCharge technology. Connect an original (or quality certified) power supply and cable. The screen should show a quick charge animation (such as "Turbo Charge" or "Mi Turbo Charge"). If the phone is charging slowly ("Charging through" USB») Even from a powerful unit, the problem may be in the connector, plume or power controller.
☑️ Checklist for battery check
Watch the phone as it charges, it shouldn't get too hot, especially in the top of the battery, overheating can indicate battery degradation or board problems, and listen to it: quiet hissing or crackling inside the case is not acceptable.
Testing of communication modules, cameras and sound
Multimedia and communication checks take time. Start with cameras: open a standard app and take some pictures in good light and low light. The photos should be clear, without soap or artifacts. Try to shoot 4K video — if the phone turns off or freezes, it's a sign of CPU problems or overheating. Check all lenses (width, TV, macro) by switching between them.
The sound is checked through a voice recorder and music playback. Turn the volume to maximum: the speaker should not wheez, rattle or distort the sound. The speaker is checked by calling another number or time service. Be sure to check the microphone by recording a voice message - you should be able to hear well without noise or interruptions.
Communication modules (Wi-Fi, Bluetooth, GPS, NFC) also require attention. Try connecting to a 5GHz Wi-Fi network, this will check the antenna. Turn on Bluetooth and try to transfer the file. To check the GPS, run the maps and wait for the location to be found - the satellites should be caught quickly enough. NFC check the payment attempt (if the card is not available, you can try emulating the intercom key, if you have the opportunity).
Why is it important to check NFC on Xiaomi?
Identification of hidden defects and restored devices
The most difficult step is to find what the seller carefully concealed. Refurbished phones are often assembled from different donors, signs of such a device can be: unoriginal assembly (backlash, gaps), different screen shade from frames, lack of moisture protection (checking is impossible without equipment, but indirectly - no markings or traces of moisture), and should be alerted too low price for the stated equipment.
Check the sensors through the same engineering menu. Swipe your hand over the light sensor -- the numbers must change. Check the vibrator motor: it must work clearly, without any outside clang. If your phone has an IR port, try using it as a remote, a unique feature of Xiaomi that you often forget to check.
Be sure to connect your phone to your computer and run the Mi PC Suite or just look at the device's properties in Device Manager. The computer must correctly identify the model. You can also use third-party utilities like CPU-Z or AIDA64 to check the claimed characteristics (RAM volume, CPU type) with real ones. There are times when a re-imbursed budgetary is sold as a flagship.
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The main sign of high-quality used Xiaomi is a transparent history and the absence of traces of interference in the system (no root rights, unlocked bootloader, if this is not agreed).
Final Software Verification
Before buying, make sure to reset your phone (Settings → About phone → Factory reset) in the presence of the seller, which will delete all other people’s accounts, passwords and possible miner viruses that may have been installed before. After the reset, the phone must reboot and prompt you to choose a language. If after the reset, a request for a Mi Account that you can’t bypass, the transaction is canceled.
Check the software version. Go to Settings → About phone. If it says “Global Stable” but there are Chinese apps or strange fonts on the menu — probably a re-shopped Chinese version. These devices may have problems with notifications (Google’s push services may not work well) and banking applications (SafetyNet/Play Integrity may not work).
⚠️ Avoid buying phones with an unlocked bootloader unless you are an experienced user. This reduces data security, makes the device vulnerable to account theft, and can lead to denial of warranty service (if the warranty is still relevant) and problems with the operation of some banking applications.
In the initial setup process, after the reset, try connecting to Wi-Fi and logging into your Google account. This is the final test for the performance of network modules and the absence of locks from Google (FRP Lock). If the phone goes through all the stages, runs quickly, does not bask in simple and pleases the quality of the screen — congratulations, you found a great copy!