iPhone Logic Board Repair (2016)
2. The logic board
In this chapter I will discuss how a logic boards works and how its main components operate .
2.1 The circuit
All iPhone logic boards have basically the same layout. There is a battery that provides current that flows through the board which provides energy and data to the components to function. You can compare this to the blood flow inside a body threw veins, in order to feed the organs. The current flows through so called traces inside the board. These traces sometimes reach the surface. The point where a trace reached the surface is called a pad. The components are soldered onto these pads. If a component or trace gets damaged the current flow stops, or is (partly) blocked, and needs repair.
Another part of the logic board is called ground (GND). This is the metallic part of the board that isn’t supposed to carry current. Most GND is. If a current flow accidentally contacts GND you have a short and loss of energy. This normally creates heat , and causes malfunctions.
The most important parts of the board are the IC’s. You can compare them to the organs inside a body and they provide the functions needed for a iPhone to operate. They work in concert with other components like filters, capacitors, resistors, diode’s and coils. Some of the most important IC’s in logic board repair are: the Power Management IC (PMIC), the NAND Flash IC, the Processor IC, the charge IC, the touch IC’s and the backlight driver IC. See the following picture for these IC’s on the iPhone 6.
The place where the logic board can connect to extern hardware is called the connecter. It transports current form and unto the extern hardware. They are a common cause of malfunction.
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2.5 Additional components
The additional components are for altering the current flow. I will next discuss their main function and I will provide pictures for their recognition.
The main purpose of a filter is filtering the current flow. Most of the times it is located near to a connector. They are the ones which often get damaged first. They also provide protection (like a fuse) against current spikes to other parts on the same circuit line like IC’s.
The purpose of a capacitor is to store electronic energy for a certain amount of time. They have one side on a line pad and the other on a GND pad. If they somehow get damaged they can short the line to GND and cause little or bigger malfunctions.
The purpose of a resistor is to diminish current flow or voltages on a line.
The purpose of a diode is to pass current in one a way and to block it in the other way. Like a valve.
The purpose of a coil is to amplify or diminish voltage. It is needed for creating high voltages like for powering the backlight.