Buying a smartphone in the secondary market is always a lottery, where the risk of running into a restored or problematic device is especially high. The market in 2020 is full of models that have already passed through the hands of the first owners, which means that they have hidden defects or signs of active use. Careful diagnosis before transferring money can save you from buying a brick or device with replaced components.
Many models released during this period, such as the Xiaomi Mi 10, Redmi Note 9 Pro or Poco F2 Pro, are still relevant in their characteristics, but their condition can be radically different. It is important not just to turn on the phone, but to conduct a deep analysis of its hardware and software shell. In this article, we will discuss all the nuances that will help you make an informed decision.
Don't rely on the seller's assurances that the phone was "a girl" or "laid in the closet"; only special codes, an engineering menu and a physical examination will show the real picture. The critical step is to check the IMEI on the box, in the system and on the engineering menu, since discrepancies here often indicate artisanal repairs or stolen devices.
External inspection and inspection of the hull
The first step is to start with visual analysis. Even if the seller claims to have carried the phone in a case, traces of exploitation are almost always visible in good lighting. Check the ends of the case and connectors for scuffs, chips or dents. The presence of scratches around the camera lens is often indicative of carelessness.
Pay special attention to the joints between the frame and the screen, and the back cover. If you notice gaps, sticking glue or irregular indentations, this is a sure sign that the device was opened. The seal of the factory assembly should not be violated, and any interference could lead to damage to the plumes or moisture entering the interior.
Check the volume control and on buttons. They should have a clear, elastic stroke. Luft, sticking or pressing too tightly indicates wear of the mechanisms or moisture. Also check the USB Type-C charging connector: there should be no oxides, dirt or strain of the contacts inside.
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Use the flashlight of another phone to illuminate the connectors and speaker – so you can see the dust and oxidation of the contacts, which are not noticeable in ordinary light.
The glass of the cameras must be clean and crackless. Even a microscopic chip on the main camera's protective glass can lead to glare in photos or focusing errors. SIM-The cards open smoothly and fit tightly in a closed state.
Diagnostics of the display and touch screen
The screen is the most expensive and vulnerable element of the smartphone. In 2020, many Xiaomi models were equipped with AMOLED arrays that are prone to pixel burnout. Turn on the white image at maximum brightness and carefully examine the screen. If you notice pinkish or yellowish spots, then the resource of the pixels is already partially exhausted.
To do this, type ##6484## in the call app. This will open CIT (Customer Inspection Test) and select the Touch or Touchpanel test and swipe your finger through all sectors of the screen. The line should be continuous, without breaks or spontaneous jumps.
- 🔍 Check for “dead zones” where the screen does not respond to touch.
- 🎨 Evaluate the uniformity of the lighting and the absence of color stripes.
- 🖐️ Make sure the multi-touch is working correctly (can be checked in-game or in-game test).
If the display has been changed, this is often indicated by a less saturated color or difference in the shade temperature from the factory settings. Xiaomi's original screens have excellent calibration, which is difficult to repeat in cheap analogues. Also check the proximity sensor: hold your finger to the upper end during the call, the screen should go out.
IMEI verification and device authentication
One of the most important steps is to verify the device on the back (or on the tray). SIM-maps in new models) and the box should be indicated IMEI. The same number is duplicated in the system. Type *#06# and compare the numbers to the ones on the box.
But matching numbers doesn't guarantee originality. Chinese craftsmen have learned to stitch IMEIs onto copies. So be sure to go to Xiaomi's official verification site and type in the code. The system should show the model, color and activation date. If the site says "not found" or shows another model, you have a fake or a machine with "broken" firmware.
Note the Mi Account status. If the phone is tied to someone else's account, the seller must untie it in front of you. Otherwise, after resetting, the device will lock and you will not be able to use it. Demand a complete logout from all Google and Mi accounts before buying.
| Parameter | Original | Quality copy | Low-quality copy |
|---|---|---|---|
| Mi logo | Clear, smooth, under glass | Painted. | Erased or curved |
| Settings menu | Adapted, no Chinese characters (in Global) | There may be artifacts of translation | Chinese, strange fonts, strange fonts |
| Camera. | Clear photo, zoom works | Interpolation, zoom soap | One work camera, the rest of the decor |
| Speed of operation | Quick interface response | Slowdowns in heavy applications | Lags are even on the menu. |
Testing of cameras and multimedia
The camera is one of Xiaomi's top smartphone trump cards: Launch the camera app and take some pictures in good light and when it's not enough. Pay attention to the focus speed. If the camera is looking for focus for a long time, this may indicate problems with the autofocus module or software failures.
Check all lenses if there are multiple lenses. Switch between wide-angle, main and telephoto lenses. The image should be clear, without black spots (dust on the matrix) and stripes. Video shooting is a great test of performance: try recording video in 4K 60 fps. If the phone starts to warm up a lot or the recording is interrupted, there may be problems with the cooling system or the processor.
The secret of checking the speakers
Remember to check the microphones. Record the dictaphone note in a quiet, noisy room. The sound should be clean, without severe interference. Also test the vibration: it should be palpable, but not sluggish. A weak vibration can indicate wear of the motor.
Checking the headphones is also important, especially if there are none in the kit and you'll be using yours.Put in the plug or plug in the Bluetooth headset.The sound should be stereo, without skewing into one channel.The 3.5mm connector (if any) should sit tight, without backlash.
Analysis of battery status and charging
Battery is a consumable, and by 2026, the batteries of the 2020 models could already have lost a significant amount of capacity, a standard loss of about 20% in two to three years of active use, and you can check the exact wear through the engineering menu or special applications, but the most reliable way is a time test.
Put your phone on charge and time tag. Original Quick Charge or Power Delivery fast-charging devices should show the corresponding status on the screen (like Quick Charge or Turbo charge). If the phone charges slowly, try replacing the cable, but if the problem persists, the power controller or battery itself may be worn out.
- 🔋 Check the heating of the case during charging (let us assume light heating in the area of the camera).
- ⚡ Make sure the phone does not discharge on its own when turned off.
- 📉 Pay attention to the jumps in percentage charge (for example, from 40% sharply to 15%).
Battery bloating is a critical defect. Put your phone on a flat surface and try to spin it. If it spins like a jula, it's a swelling battery that's pressing on the back cover, and you can't buy one of these phones because it's fire-prone.
☑️ Checklist for battery check
Checking communications, Wi-Fi and sensors
The smartphone has to ring and go online. Put your own. SIM-Check the signal level, run a test call to see if the connection is good, switch the mobile Internet to the Internet. 4G/LTE And check the speed of the pages, and the antenna problems often manifest themselves in constant communication interruptions or inability to catch the network where other phones are working.
Wi-Fi and Bluetooth testing is also mandatory. Connect to a wireless network, walk around the apartment. The signal should not be lost in the next room. Turn on Bluetooth and try to transfer the file to another device or connect the headphones. Sound delay or connection breaks will indicate a malfunction of the module.
⚠️ Note: If the Wi-Fi connection starts to warm up strongly in the upper part (where the antenna is located), this may indicate a short circuit in the power supply of the communication module.
Be sure to check all sensors through the engineering menu (##6484##). Accelerometer, gyroscope, compass, light sensor – all of them must respond to changes in position and environment. A faulty gyroscope, for example, will make it impossible to use the navigator in 3D mode or some games.
Programming and the presence of hidden problems
Check the firmware version. Go to Settings → About the phone. It should indicate which version is installed: Global, China or EU. If the seller says it is Global, and in the settings Chinese characters or the Mi Store app store instead of Google Play, you are being deceived. Flashing from Chinese to global often requires unlocking the bootloader, which does not always go smoothly.
Try resetting to factory settings right at the seller, which will delete all of the seller's data and show if the device has hidden locks or viruses, and if the phone requires a password from the previous owner's account after the reset, the deal won't happen until he enters it.
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Resetting to factory settings is the only way to ensure that the device is free of other people’s accounts, hidden spy apps or system errors caused by third-party software.
Check for root rights. Having superuser rights often means that the phone was used by enthusiasts, could change system files, which reduces the stability of the work. For the average user, having root is more a risk than an advantage.
How to quickly check for Root rights?
What to do if IMEI is not readable?
Can I check my phone without SIM-map?
Is it OK if the 2020 phone has scuffles?
Buying a used Xiaomi smartphone is a great way to save money by getting a powerful device. But saving should not turn into buying a problem device. Careful checking on the items described above will take only 15-20 minutes, but will save your nerves and money. Feel free to ask questions to the seller and demand time for diagnosis - an honest owner has nothing to hide.