Diagnostics, Troubleshooting and Repair of Cell Phones

Hello, in this article we tell how to fix and diagnostics cell phone. Like any complex technique, cell phones often fail when used actively. This can happen for a variety of reasons, such as factory marriages, long service lives or the careless handling of the owner with the phone. The main reasons for the breakdown are frequent falls, water entering the phone, bathing the phone in water (fell into the river, got into the washing machine), non-observance of the rules of operation of a particular model or simple negligence, because many phone models are very fragile in circulation. For example, clamshell models are often broken by carelessness.

If the phone breaks down, the owner begins to look for a repair location for cell phones and comes to the service center to a repairman for help. And in this situation, the master must quickly and skillfully conduct a primary diagnosis of the cell phone and repair it if necessary.

In general, the diagnosis of malfunctions is a kind of art, based, first of all, on a deep understanding of the operating principles of the device. Without this, it is impossible to master the art of repair perfectly. Below we give a general approach to the repair procedure using the example of the Nokia 6020 phone, and training in our courses, as well as your patience, accuracy and attentiveness will allow you to gain experience and polish your skills.

Malfunctions of mobile phones can be conditionally divided into three types:
– mechanical damage;
– failure of electronic components;
– Incorrect operation of the phone software.

Mechanical damage
Mechanical damage is detected by visual inspection, including by means of optical instruments – a magnifying glass and a microscope. It should be noted that even small external damages that appear after the impact or fall of the phone, as a result, can lead to the formation of a microcrack in some contact track, which in turn leads to a total inoperability of the phone. Most often, the chips suffer from the chips of transmitters and antenna switches assembled on a ceramic base.

Failure of electronic components
Universal Test
The failure of electronic components, as a rule, is accompanied by a change in the current consumed by the phone. There are so-called rapid tests, which are based on the measurement of the current consumed. Some manufacturers, such as Nokia, in the technical manuals give algorithms for such tests. However, as a result of the test, we can only talk about the probability of failure of one or another element, although this probability can be quite high. For testing, it is necessary to take out the battery and connect an external power supply with a voltage of 4.2 V to the battery contacts of the phone, preferably it is a stabilized power source, with indication of the current output.

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The phone is switched off.
The current consumed by the switched off phone is 0. In the phones, two chips are directly connected to the battery – a power amplifier (transmitter) and a power controller. A faulty power controller consumes approximately 300 – 400 mA, and a faulty power amplifier may give a short-circuit (short circuit). That is, if the phone immediately consumes 300-400 mA when it connects to the power source (we do not press the power button at the same time), then the power controller is likely to be faulty and it needs to be replaced, in this model the power controller is called UEM. And if, when connected, the power supply stabilizes and stops feeding current to the phone, and the multimeter in the continuity mode shows a low resistance and “peeps”, it is possible to remove the power amplifier and check the phone for activation. If the phone is switched on, then we install a new power amplifier.

The initial current is 0.
Push the power button. If the current is still 0, then either the breaker, the closing circuit, or the power controller is faulty. You can check this chain by disassembling the phone.

Start disassembling the phone
Next, you should visually inspect the power button. Then you need to measure the voltage on it, if the voltage on it is (about 4 volts) and when you press it it drops to zero, then the switching circuit is working. In this case, the UEM power controller is likely to be defective or undamaged.

The UEM power controller can be soldered with a thermo-foam from a Lukey-702 soldering station. We will put on the microcircuit a little flux-free flux.

Let’s install the thermofan to a temperature of about 280 ° C. Carefully warm up the microcircuit. After warming up, it is necessary to clean the board with a spray-cleaning board, for example, FLUX-OFF

After that, the phone either turns on, or it can drive as follows.
If the current is approximately 50 mA when the button is pressed and disappears before the button is released, the program in the FLASH memory is faulty. In this case, the phone must be reprogrammed. To do this, we need a UFS programmer with HWK and an f-bus cable to connect the phone to the programmer.

Also we will need a firmware for this phone with the latest version.

We connect the programmer to the computer, install the latest drivers, the latest version of the program for this programmer, perform an update for it (if required). Open the program DCTxBB5, click on the button Connect, so we connect the program with the box (programmer). Next, choose the platform, in our case it’s DCT-4, and select the model you want.

Then click on the Check button to check the cable’s contact with the phone, and also send the loader to the processor. If the processor and flash memory are healthy, then we will see information about this in the program window, if an error is displayed instead of the information, then, probably, we need a replacement or restoration of the processor and / or flash memory mounting.

If the information about the processor and flash memory is displayed, then let’s try to flash the phone. We select in the corresponding windows the firmware files of the main program code (MCU), the language package (PPM), in our case with the Russian language (about the letter “K” at the end of the file name) and the content (CNT) (naturally, also with the Russian language). Versions of MCU, PPM and CNT must match.

Then click the FLASH button to start the firmware process.
If errors occurred during the firmware process, then hardware repair of the processor part and further flashing are necessary.
At the end of the firmware process, we try to turn on our phone. If the result is negative, then hardware repair and more subtle diagnostics are required.

Conclusion
In this article, we talked about the very first steps in the surface diagnostics and repair of telephones. For a deeper diagnosis, additional equipment, electrical circuits, the ability to read and understand them are required.

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