The basics of circuitry

Максим Исаев
Reading time: 3 min

Electronic component


Capacitor (C) – a radio component designed for charge accumulation. In circuit engineering, another important property of the capacitor is used-it quickly gives off a charge (discharge) when the consumer of electrical energy is switched on. In order to check the capacitor for a short circuit, it is necessary to solder it out of the circuit and make measurements with a multimeter in the ringing mode. The capacitance of the capacitor depends on several factors. One of them is the geometric dimensions of the capacitor plates.


The coil (Fl) – filter or fuse-is designed to protect the circuit from the effects of high currents. It is a self-destructing element and is used for disconnecting a closed circuit by opening it. The filter is checked by a multimeter in the “Ring” mode of the circuit for integrity.


Resistor (R-designation in the scheme) – for linear conversion of current to voltage and Vice versa. As well as for limiting the current in the electrical circuit. Instead of a resistor with zero resistance, it is allowed to install a jumper, only for the time of diagnostics. After conducting Troubleshooting activities on the phone Board, install R to its place in the circuit. If the resistor is damaged, then take it from the” donor ” Board.


Inductor (L) – designed to smooth out interference, as well as to maintain the current value in the electrical circuit. The inductor is checked by a multimeter in the “Ring” mode.


Diode (D) – conducts an electric current in one direction. That is, if during measurements, the diode passes current in the opposite direction, it means it is faulty. Used in the illumination unit of the phone. Structurally, it has 3 outputs. An anode and two cathodes. The diode is checked for serviceability by a multimeter in the mode of diode ringing.

The polarity of the diode can be determined:

  • key (label) on the cathode,
  • multimeter in the mode of diode ringing,
  • visually, on a non-soldered “donor” Board.


The main purpose of the transistor (Q) is to control the current in the output circuit. For example, in the iPhone 5S, a Q2 transistor is installed in the charge circuit.

IPhone chips


One of the purposes of TRISTAR (U2 in iPhone 5S or U1700 in iPhone 6) is to determine the accessory connected to the phone (headphones or Lightning). After replacing the USB controller, to check that the chip is working properly, you need to connect your phone to the USB-tester and check the synchronization with your laptop.


The OSCAR chip (U2201 in the iPhone 6) collects information from sensors and transmits it to the CPU.

Instead of conclusion: basics of circuit design

The article provides basic information that is studied in the training courses for soldering and diagnostics of circuit boards. This is a necessary material for understanding the diagnostics of a phone or laptop system Board.

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