The used electronics market is booming, and Xiaomi smartphones are leading the way because of their high price-performance ratio. Buying a handheld device saves up to 40-50% of the cost of a new model while providing flagship features that are not available in the budget segment of new equipment. However, it is the brand’s popularity that attracts scammers and resellers selling restored or problematic gadgets under the guise of “near new”.
The problem is that a functional machine can have hidden iron defects or software limitations that the seller is silent about. AMOLED-screen, water flooding in the past or, most unpleasantly, binding to someone else's account Mi. Without careful verification, you risk turning a profitable deal into a constant fight against system glitches.
In this article, we'll look at all the nuances of diagnostics, from visual inspection to the use of engineering menus, you'll learn to identify glued displays, check the number of charging cycles, and determine whether your phone is wanted. A competent approach to choosing will allow you to purchase a reliable assistant that will last for many years, and will not become a source of headache.
Visual diagnostics of the case and screen
The first meeting with a potential purchase should be in good daylight, as artificial light often hides small defects. Carefully examine the device ends, charging connectors and speakers for scuffs and chips. The presence of scratches around the lens of the main camera often indicates that the phone was dropped and the impact occurred on this area, which could damage the optics stabilizer.
Pay special attention to the screen. When turned off, hold your phone to the light and look at it from an angle: the AMOLED arrays used in most modern Xiaomi often show cracks or black spots that are invisible when you look at the screen, if the screen has been changed, the gaps between the frame and the glass can be uneven, and the color reproduction can be different from the reference one.
⚠️ Warning: If the seller claims to have put on the protective glass immediately after purchase, ask to remove it or at least show the edges.
Check the waterproofing by indirect methods. SIM-maps: if the rubber seal inside the tray is deformed, dried or missing, the phone is likely to have been opened or exposed to moisture. USB-C: The oxidation of contacts speaks for itself.
Checking the display for burnout and touch screen
The screen is the most expensive component of a smartphone, and its condition directly affects the comfort of use. On panels like AMOLED, over time, the burn-in effect can manifest itself, when static interface elements (state bar, navigation buttons) leave a barely noticeable trace. To check this, open a pure white image at maximum brightness.
Touchscreen testing is best done using Xiaomi’s built-in engineering menu, which is the most reliable way to make sure all zones are responsive to touch and there are no “dead” areas. Enter the code ##6484## in the Caller app to switch to CIT (Customer Integration Test).
In the test menu, select the item associated with the display (usually called "Display" or "Touch"). Swipe your finger over the entire surface: the line should be solid, without breaks and jumps. Also check the multi-touch operation by touching the screen with several fingers at the same time - the smartphone should correctly display all the dots.
- 🔍 Look for uneven backlighting: Turn on a dark theme and view the screen in the dark - there should be no bright spots or "clouds».
- 👆 Sensitivity Test: Try typing text quickly or drawing complex shapes to detect reaction delays.
- 🌈 Color rendering check: Compare the display of colors to another serviceable Xiaomi phone of the same series, if possible.
Diagnosis of the battery and charging
Battery status is one of the main criteria when buying used equipment. Lithium-ion batteries degrade over time, regardless of whether you used the phone or it was on the shelf. In Xiaomi smartphones, you can find out the exact state of the battery through an engineering menu or special utilities.
In the same CIT menu (call ##6484##), find the Battery or Battery Indicator section, which shows the current status, voltage and, most importantly, the number of charging cycles. If the meter shows more than 500 cycles, the actual battery capacity could drop to 80% or below, leading to a quick discharge.
Be sure to check the fast charging. Connect the original (or certified) power supply and cable. The Mi Turbo Charge logo (Quick Charge) should appear on the screen. If charging is slow or interrupted when the cable is moving, the problem may be the connector or the power controller.
Also pay attention to heating. When used actively or fast, the phone should not become scorching hot at the top of where the battery is located. Excessive heating may indicate an internal short circuit or degradation of battery chemistry.
| Parameter | Norma. | Critical (rejection) |
|---|---|---|
| Charging cycles | 0 - 300 | More than 500. |
| Residual receptacle | 90-100% | Less than 80% |
| Tension at rest | 3.7B - 4.2B | Below 3.5B |
| Charging speed | Conforms to the stated | Only 5B/1A |
Checking cameras, speakers and microphones
Multimedia is something we love about modern smartphones, so checking cameras is a must. Open the Camera app and switch to all the lenses in sequence: main, wide-angle, TV and macro. Take pictures of a white sheet of paper that show the dust under the lenses or the defects in the matrix.
Record a short video using each microphone. The main microphone is on the bottom, the top (noise suppressing) is on the end, and the third can be integrated into the body. Speak to the phone with your finger covering the different holes to make sure the sound is recorded and transmitted on the air.
Speakers are checked for maximum volume. Turn on music with a wide frequency range. Wheezing, rattling or "crowding" sound indicates that the speaker is either worn out or was filled with liquid in the past. Vibromotor should also work clearly, without extraneous friction sounds.
⚠️ Attention: If the camera focuses in jerks, emits a mechanical crack or the image "floats" with the stabilizer on, most likely, the camera module is physically damaged.
Don't forget to check the sensors. Hold your phone to your ear when you call, the screen should go out (the proximity sensor is working). Check the autobrightness by covering the top of the screen with your hand. Sensor failures can make using the phone extremely uncomfortable.
Search for hidden blockings and account status
The most dangerous scenario when buying a used Xiaomi is to purchase a device with a link to someone else's Mi Account, the owner can remotely lock the device, turning it into a "brick", even after resetting the settings, the "Find the device" function must be disabled before selling.
To check the settings of the phone: Settings → Mi Account. If it shows someone else’s email or phone number, ask him to untie it with you. After that, be sure to perform a full reset (Wipe Data) and the first activation enter your data.
Check status. IMEI It's on the official Xiaomi website or through special services, which will let you know if the phone is listed in the database of stolen or lost devices. IMEI, slacked SIM-cards (if any), in the settings About the phone and on the box - they must match.
If the phone was bought on credit, it can also be blocked by the bank. Make sure the device is not collateral. Ask the seller for a purchase check or a contract proving ownership, although this is rare in the secondary market.
Software analysis and firmware reflashing
Many Xiaomi used products are imported from China and have a global firmware installed by the vendor. This is normal practice, but it is important to understand how the software was changed. If the global version (Global ROM) was put on top of the Chinese version by unlocking the bootloader, the bootloader menu (Loudness Down + Power buttons) will be an orange warning.
Having an unlocked bootloader reduces device security and can cause problems with banking applications (Google Pay, Mir Pay), although workarounds exist. In addition, over-stitched phones may not receive over-the-air updates (OTAs).
Version check: Settings → About the phone → MIUI versionNotice that there are fewer ads in system applications, but if you have custom built them, you can build them on a system level, and check if Google services work, because some Chinese versions need to be installed separately.
In conclusion, take your time to buy. A thorough check of all features will take 15-20 minutes, but will save you from losing money. If the seller refuses to diagnose or rushes, this is a sure sign that something is wrong with the phone.