Modern smartphones are unthinkable without a high-quality display, which is the main window into interaction with the device. When screen starts to act up, the user instantly loses contact with the outside world, since 99% of all operations are tied to the visual display of information. The first signs of a malfunction may be subtle changes in color rendition or rare missed clicks, which are easy to ignore for the time being.
Diagnostics of the state of the matrix and touch layer is not just a whim of a perfectionist, but a necessary measure when buying a used device or identifying the causes of strange system behavior. There are many ways checks, ranging from built-in engineering menus accessible through special codes, to installing specialized applications from Google Play. In this article, we will analyze all the available methods so that you can determine exactly where the problem lies.
Do not delay checking if you notice “ghost” touches or a change in the shade of white, as these symptoms often progress. Timely diagnostics will help you understand whether software calibration is required or whether an expensive module needs to be replaced. Let's look at the tools that will help you conduct a professional inspection of your gadget.
Built-in engineering diagnostics through codes
The fastest way to access the hidden functions of the device is to use USSD commands that open the engineering menu. This is a system section intended for testing engineers, where you can run automatic checks hardware without installing third-party software. To launch the tester, you usually need to dial a special code in the Phone application, after which a menu will open with buttons for testing various components.
The codes may vary depending on the manufacturer and shell version Android. For example, on devices Xiaomi the combination is often used ##6484##, and on Samsung — #0#. On pure Android (Pixel, Motorola) access may be limited, but it's worth a try. If the code does not work, the manufacturer may have blocked access to this section for regular users.
⚠️ Attention: Be careful in the engineering menu. Changing settings in sections marked "Config" or "Network" may result in network settings being reset or the radio module not operating correctly. Use only testing functions (Test/Check).
What to do if the code does not work?
If standard codes do not open the menu, try entering them without asterisks at the end or using call emulator applications that force a USSD request. Also, access may be blocked by the telecom operator or firmware.
Inside the diagnostic menu, you will be offered tests for each component separately. To check the display, you usually select "Display", "Screen" or "RGB". The system will automatically run the color screens, check the response to touches and display the result as “Pass” (success) or “Fail” (error). This is a basic level that helps to quickly eliminate critical failures.
Checking for broken and stuck pixels
One of the most common problems with matrices is defective dots that do not change their color or luminosity. Dead pixels are pixels that are permanently black and do not light up, while “stuck pixels” can glow red, green or blue even when they should be off. To detect them, you need to carefully examine the screen against a plain background.
There are several methods for identifying such defects. The easiest way is to take a screenshot of pure white, black and color pictures, and then view them in full screen mode, bringing your face as close to the display as possible. You can also use online services that fill the screen with a specific color, or download specialized applications from the market.
- 🔴 Red/Green/Blue: Check each primary color separately, since the defect can only appear in one channel.
- ⚫ Black color: Ideal for finding luminous points in the dark that indicate glare or loose fit of the matrix.
- ⚪ White color: Helps to identify dark spots and uneven backlighting along the edges of the screen.
If you find one or two stuck pixels, do not immediately panic. Sometimes gentle massage of the defect area (through a cloth) or the use of apps that quickly change colors in this area, “swinging” the crystals, helps. However, if there are many defective dots or they appear in groups, this is a sign of physical degradation of the matrix, and here software methods are no longer effective.
For the most accurate check for dead pixels, use a magnifying glass or macro photography on the camera of another phone. The human eye may not notice a micro-defect on modern high-resolution matrices (Full HD and higher).
Sensor and multi-touch diagnostics
Problems with the touchscan (sensor layer) often do not appear immediately. The device may begin to ignore touches on the edges, respond incorrectly to multi-touch, or perform actions on its own (“ghost touch”). To check the accuracy and responsiveness of the sensor, graphical tests that visualize touch zones are best suited.
One of the simplest ways to check with built-in tools is to use the developer menu. To activate it, you need to go to Settings → About phone and quickly click on "Build number" 7 times. After this, a new item “For Developers” will appear in the settings menu, where you need to find the option “Show touches” or “Pointer location”.
When this function is activated, a line following your finger will be displayed on the screen. This allows you to see if there are breaks in the line, jumps in coordinates, or erratic touches that you did not make. If the line is interrupted or jerks for no apparent reason, the problem may be a poor-quality protective glass, poor contact of the cable, or damage to the digitizer.
☑️ Checking the sensor
Special attention should be paid to the multi-touch test. Modern screens support from 5 to 10 simultaneous touches. To check, launch a game or application that supports multi-touch and touch the screen with all your fingers at once. If the system registers fewer touches than you made, or the cursors “jump”, the touchscreen controller does not work correctly.
Using third-party applications for testing
If the built-in tools are not enough, specialized utilities from Google Play come to the rescue. They provide more detailed statistics and automate the verification process. Applications like TestM, Phone Doctor Plus or Screen Test.
are popular. Such apps often have an integrated approach: they check not only the screen, but also the operation of the accelerometer, gyroscope, speakers and microphone. This is convenient when buying a used phone, when you need to quickly run a full diagnostic cycle. Applications provide a report in the form of percent health or a list of errors.
| Application | Main function | Presence of advertising | Weight (approximately) |
|---|---|---|---|
| TestM | Full hardware diagnostics | Yes | 15 MB |
| Screen Test | Test colors and gradients | No | 2 MB |
| Touch Screen Test | Multi-touch check | Minimum | 5 MB |
| Dead Pixel Test | Search defective pixels | Yes | 3 MB |
Using third-party software requires attention to permissions. Some applications may request access to contacts or geolocation, which is completely unnecessary for the screen test. Choose proven utilities with a high rating and read reviews before installation to avoid infecting your device with malware.
Visual assessment and checking for glare
In addition to software tests, visual inspection under different lighting plays an important role. Highlights (clouding) is uneven illumination, which is especially noticeable on a dark background in a darkened room. They look like light spots or “clouds”, most often along the edges or corners of the screen.
To check for glare, turn on a completely black image on your phone (you can download a black picture or video on YouTube) and reduce the brightness to minimum. In complete darkness, backlight defects become obvious. Small glare may be acceptable for IPS matrices, but if it interferes with reading text or watching video, it is considered a defect.
⚠️ Attention: Do not confuse glare with reflection of external light. For a correct test, there should be no other light sources in the room other than the smartphone screen itself. Also remove the protective glass, as it can create glare that simulates defects.
Another important aspect is checking for burn-in, which is typical for OLED and AMOLED screens. If a static element (for example, a navigation bar or keyboard icons) has been displayed on the screen for a long time, its outline may “imprint” and be visible in other colors. Light burnout can sometimes be masked by inverting colors or reducing brightness, but physically this is an irreversible process of degradation of organic LEDs.
What to do if problems are detected
If diagnostics have revealed serious problems, the algorithm of actions depends on the type of malfunction. Software glitches, such as an uncalibrated sensor or a glitchy touchscreen after an update, can often be fixed by resetting or flashing the device. In this case, a full Wipe Data (reset to factory settings) will help.
In case of physical damage (cracks, stripes on the matrix, groups of dead pixels), only replacing the module will help. If the phone is under warranty, do not try to repair it yourself or take it to questionable services - this will lead to loss of warranty status. Contact the manufacturer's authorized center.
A warranty case is a manufacturing defect (stains, stripes, non-working areas), but not mechanical damage (cracks, impacts, moisture ingress).
To temporarily solve problems with the sensor, you can use calibration through the engineering menu (item Touch Calibration) or third-party calibrator applications. However, remember that this is only a “crutch” that can extend the life of the device for a short time, but will not eliminate the cause of the breakdown.
Is it possible to restore dead pixels programmatically?
It is impossible to restore truly dead pixels (dead, black dots) programmatically, since the subpixel has burned out. However, “stuck” pixels (lighting in one color) can sometimes be revived by quickly changing colors (video strobe) within a few hours. The effectiveness of this method is about 40-50%.
Does protective glass affect the operation of the touchscreen?
Yes, poor-quality or too thick protective glass (especially with a metal frame around the edges) can shield the signal and cause “dead zones” or false alarms. If tests show problems, try removing the glass and checking the screen again.
Why does the screen react to water or moisture?
Capacitive screens work by changing the electrostatic field, which also conducts water. Drops on the screen are perceived by the sensor as finger touches. This is a normal physical phenomenon and not a defect. Waterproof phones have algorithms for ignoring moisture, but they do not work perfectly.