Posts tagged Mobile Repairing

In this article we will deal with basic electronics which is very essential for mobile repairing . Chiptroniks has emerged as the clear leader in offering quality mobile repairing course . Recently we opened our first centre in Shillong . So guys now we are opening up  anybody interested to have our Franchisee can contact us .

Mobile repairing is a combination of 2 things:

1. Hardware
   
2. Software
   

Q. What is an Atom?

A. An Atom is a smallest part of an Element which cannot be divided further. Examples are Solid, Liquid and Gaseous States.

Q. What is Voltage?

A. Voltage is the force of electrons and the unit is measured in Volts. Circuit Representation of voltage is (V).

The unit of current is measured in Amperes. The Circuit Representation of Current is (I).

Dropping of voltage is called as Resistance. Ohms is the unit of Resistance Ω. Circuit Representation of Resistance is ®.

Ohms Law

The current flowing in the circuit is directly proportional to the voltage but inversely proportional to the Resistance.

Ex.1. If voltage is 250 AC and the current is 5 Amperes calculate Resistance.

Ans: Using formula R=
-> R= Ω

Ex.2. If the voltage is 3.6 V DC and the current is 400 mA calculate resistance.

Ans: Using formula R=
-> R= Ω

Study of Multi-meter

1. Function/Range Switch: selects the function (voltmeter, ammeter, or ohmmeter) and the range for the measurement.
   
2. COM Input Terminal: Common ground, used in ALL measurements.
   
3. V Input Terminal: for voltage or resistance measurements.
   
4. 200 mA Input Terminal: for small current measurements.
   
5. 10A Input Terminal: for large current measurements.
   
6. Low Battery LCD: appears when the battery needs replacement.
   

Precautions for Current Measurements

• Turn the power off to the device and discharge any capacitors!
  
• Plug the black test lead into the COM jack.
  
• Plug the red test lead into either the
  
  • 200 mA jack for small current measurements, or the
    
  • 10 A jack for large current measurements.
    
• If you do not know the approximate current about to be measured, use the 10 A jack.
  
• Set the function/range switch to either
  
  • DC amperes in the lower right, or
    
  • AC amperes in the middle right.
    
• Break open the circuit at the point where you want to measure the current by removing one of the wires. Connect the free end of the red test lead to one place at which the wire was attached. Connect the free end of the black test lead to the other place at which the wire was attached. Current is always measured with the meter in SERIES with the device. If you do not understand the difference between SERIES and PARALLEL, ask your TA. Using the current meter incorrectly will blow the fuse or damage the meter. (It will also cost you points on your lab writeup.)
  
• Reapply the power to the device.
  
• If the LCD displays either “1.” or “-1.” with all other digits blank, the current is beyond the selected range. Use the switch to select a larger range.
  
• Once you know the approximate current through the device, then use the switch to select the lowest current range that will still accommodate the current through the device.
  
• Turn the power off to the device before removing the meter from the circuit.
  

Precautions for Resistance Measurements

• Turn the power off to the device and discharge any capacitors!
  
• Plug the black test lead into the COM jack.
  
• Plug the red test lead into the V jack.
  
• Set the function/range switch to ohms ( ) in the lower left.
  
• If you do not know the approximate resistance about to be measured, use the largest range available.
  
• Connect the free ends of the red and black test leads ACROSS the device to the measured. Resistance is always measured with the meter in PARALLEL with the device.
  
• If the LCD displays either “1.” or “-1.” with all other digits blank, the resistance is beyond the selected range. Use the switch to select a larger range.
  
• Once you know the approximate resistance of the device, then use the switch to select the lowest range that will still accommodate the resistance of the device.
  

Voltages

There are two types of voltages:

• Alternate Current (AC)
  
• Direct Current (DC)
  

AC current is a high voltage and contain frequency of 50Hz means that in a second it goes 50 times in positive and negative cycle.

Direct Current (DC) is a low voltage. Examples are Batteries (1.5 V to 24 V). It doesn’t have frequency in it.

Frequency is defined as Number of cycles per seconds.

Conventional current is a flow of current from +ve to –ve direction

Electronic Components

Electronic components are divided into two categories:

1. Passive Components
   
2. Active Components
   

The active component changes the entire function of the circuit. The examples of this are Semi-Conductors (AC to DC)

The passive component doesn’t have the ability to change the function of the circuit. It only modifies and re-modifies their respective circuits. The examples of passive components are as follows:

1. Resistors
   
2. Capacitors
   
3. Inductors
   

Resistors
Resistors are the electronic component which is used to drop the voltages. There are 3 types of Resistors:

	Resistor Type	Symbol	Circuit Symbol
1	Fixed Carbon (color Coded)
2	Variable
3	Fusable

Resistor Values

Resistor values that are available for use in circuits range from 0 to around 10,000,000.  Because dealing with large numbers like 10,000,000 is awkward, the ‘k’ prefix is used to denote 1,000 and the ‘M’ prefix is used to denote 1,000,000.  ‘k’ stands for ‘kilo’ and ‘M’ stands for mega.  Here are some examples of resistor values:

1k = 1,000 (pronounced ‘one kilo Ohm’ or ‘one k’ for short)

10M = 10,000,000 (pronounced ‘ten mega Ohms’ or ‘ten meg’ for short)

Sometimes you will see resistors quoted without the symbol, and sometimes the symbol will be replaced with ‘R’.  When a fraction is needed in a value you will often see ‘R’, ‘k’, or ‘M’ in place of the decimal point as an aid to clarity:

22k is the same as 22k

330R is the same as 330

4K7 is the same as 4.7k

Tolerance

Like all components, resistors are never perfect.  Their true value will never be exactly the same as their stated value, but will be somewhere close.  The maximum amount of error in the value is given by the ‘tolerance’ value, expressed as a percentage.  Most resistors have a 10% – 20% tolerance, and this is normally adequate for most applications.  You can get 1% and 2% tolerance resistors if you need them.

The Resistor Colour Code

Because resistors are so small, it is not easy to print their value and tolerance on them in a way which is easily readable.  Therefore, one of the following colour coding systems is used instead.  Both systems code the value in Ohms – there are no codes for ‘k’ or ‘M’.

The Four-Band System

This system uses three coloured bands to represent a resistor’s value, and an additional coloured band spaced further apart to represent a resistor’s tolerance, as shown in figure 2.

• The first two bands give the the first two digits of the resistor’s value.

• The third band is a multiplier and gives the number of zeroes that must be placed after the first two digits.
  
• The forth band gives the resistor’s tolerance as a percentage.
  

The table below shows the meaning of each colour for each of the bands.  Notice that most of the colours are in the order of the colours of a rainbow, with the exception of indigo which is not used.  There is a rhyme you can use to remember these colours: Richard Of York Gave Battle in Vain.

Exercise:

Variable Resistors

Variable Resistors are used to increase and decrease the resistances. The examples in this category are as follows:

1. Volume Control Knob
   
2. Fan Regulator
   

Fusable Resistor

The function of fusable resistor is to break the circuit when excess current flows above its specification

Inductors

Inductors are divided into two categories viz.

1. Coils
   
2. Transformers
   

Coils

Symbol:

Circuit Representation: (L)

Unit of Measurement: Henry

The function of coil is to filter the voltage. When voltage is applied to a coil EMF (Electro Motive Force) is generated.

Transformers

The function of transformer is to transform on energy into another. It steps up and down the voltage. Every electronic and electrical device has their specification mentioned on the back panel on their respective bodies. So for replacement of the Transformer of a particular device if it gets faulty, the same value unit of transformer should be replaced.

Transformers are further divided into two categories viz.

1. Step-Up (Example: EHT (Extra High Tension)
   
2. Step-Down
   

Step-Down Transformer

Step-down transformers are further divided into two categories:

1. Conventional
   
2. Center-Tap Transformer
   

Conventional Transformer

low voltage is passed from primary to secondary winding. For Example, a step down transformer of 4.6 V AC requires 240 V AC at the primary winding which is stepped down to 4.6 V AC at the secondary winding.

To find out which is the primary and secondary winding in Conventional Transformer use Multi meter and keep it in buzzer mode. Place the testing probes on either side, if buzzer is heard then that is Secondary Winding.

Center-Tap Transformer

Center-tap Transformer has a center winding of 0 V, in other words we can say that the secondary winding contains 3 wires, the center on is 0 Volts. Refer the diagram for more.

Capacitors

The function of capacitor is to pass the AC voltage and store the DC voltage. Capacitors are further divided into two categories:

1. Polarized
   
2. Non-Polarized
   

Polarized Capacitors

Symbol:

Looks:

Unit: Micro Fared (µf)

Internals of Electrolytic Capacitors

Non-Polarized Capacitors

Symbol:

Looks:

Non-polarized capacitors are disc or ceramic capacitors. The unit is Pico fared.

Semi Conductors

Semi conductors are the elements which are partly conductors and partly insulators. Example of element is Silicon. The examples of semi-conductors are as follows:

1. Diodes
   
2. Transistors
   
3. I.C. (Integrated Circuits)
   

Diodes

Diodes are semi conductor components which converts AC to DC (Rectifier Ciruits). It has 3 major components:

1. P.N. Junction
   
2. Zener Diode
   
3. L.E.D. (Light Emitting Diode)
   

P.N. Junction Diode

Symbol:    Layout:

Internals:

When we check a diode on a multi meter on buzzer mode, by placing the red probe on the positive side and black probe on the negative side, we hear buzzer. It means that the diode is Forward Bias. If we place the testing probe in the reverse order, we do not hear buzzer, it means that the diode is reverse bias. It indicates that diode works in one direction i.e. from Positive to negative which is called as Forward Bias. P.N. Junction diodes convert AC to DC (Rectifier Circuit)

Zener Diode

Symbol:    Layout:

Zener diode acts as a voltage stabilizer. It comes under different voltages such as 5 V, 10 V, 12 V etc.

L.E.D. (Light Emitting Diode)

Symbol:    Layout:

The function of LED is that it emits light when voltage is passed to it. It is used as a power indicator in the circuit. It operates under 1.5 V DC and comes under different colors such as Red, Yellow, Green, Blue.

Rectifier Circuits

Rectifiers are the circuit which converts AC to DC voltage. The are 3 types of Rectifier Circuits:

1. Half Wave Rectifier
   
2. Full Wave Rectifier
   
3. Bridge Rectifier
   

Half Wave Rectifier (Preparation of Mobile Charger)

Requirements to make Half Wave Rectifier

1. Conventional Transformer 6 V AC / 1 Amp.
   
2. PN Junction Diode (1 Nos.)
   
3. Electrolytic Capacitor 10V/220 MFD
   
4. Zener Diode
   
5. Resistor (Voltage Drop at LED)
   
6. LED (Power Indicator)
   

Circuit Diagram

Preparation of Mobile Charger

The Half Wave Rectifier is a circuit which converts AC to DC voltage. In this circuit, only one P.N. Junction Diode is used. The internal Resistance of Primary Winding of a transformer is very high because of this the voltage is dropped to 6 volts AC. In between the core of Primary Winding and Secondary Winding, EMF is generated and the voltage is transferred to the secondary winding. At the output of secondary winding, we get step down voltage of 6 V AC form (It will have 50 Hz. Frequency).

So a PN Junction Diode is connected in series. The diode will only forward bias the positive half cycle of AC voltage. But there are chances of AC Leakage (Ripples) which may damage the battery at the time of charging. Therefore, an Electrolytic Capacitor is used to bypass DC and block AC voltage.

A Zener Diode is used to stabilize the voltage. It is of 6 V. The Zener diode will start working when more than 6V is applied to it. It will break the circuit when excess voltage comes. LED is used as a power indicator and a Resistor is attached to it to drop the voltage because LED works on 1.5 V and our circuit is of 6V.

Hence a charger is prepared successfully.

Full Wave Rectifier

Requirements to make Full Wave Rectifier

1. Center Tap Transformer 6-0-6 V AC / 1 Amp.
   
2. PN Junction Diode (2 Nos.)
   
3. Electrolytic Capacitor 10V/220 MFD
   
4. Zener Diode
   
5. Resistor (Voltage Drop at LED)
   
6. LED (Power Indicator)
   

Circuit Diagram

With Respect to half wave rectifier this gives better performance because at the same time 2 diodes are Forward Bias so we get double positive half cycle. This minimizes the AC Leakage chances. Rest of the circuit is same.

Bridge Rectifier

Requirements to make Bridge Wave Rectifier

1. Conventional Transformer 6 V AC / 1 Amp.
   
2. PN Junction Diode (4 Nos.) or Bridge Rectifier Module.
   
3. Electrolytic Capacitor 10V/220 MFD
   
4. Zener Diode
   
5. Resistor (Voltage Drop at LED)
   
6. LED (Power Indicator)
   

Circuit Diagram (Using PN Junction Diodes)

Circuit Diagram (Using Bridge Rectifier Module)

Bridge Rectifier gives the same performance of the full wave rectifier. This circuit can be prepared by using conventional tansformer using Bridge Rectifier Module and rest remain same.

Transistors

Transistor acts as an open switch. The input voltage is a form of AC which is given to the base of Transistor. Transistor are used for amplification of the signal (Convert Weak signals into stronger signals)

Transistors are further divided into 2 categories:

1. NPN
   
2. PNP
   

NPN Transistors

Symbol:    Layout:

When we check a NPN transistor on a Multimeter by keep the red probe on the base of the transistor and the black probe on either Collector or Emitter, we can hear buzzer. This indicates the following:

1. Base to Collector: Forward Bias
   
2. Base to Emitter: Forward Bias
   

When do this in reverse order, we do not hear buzzer. This indicates the following:

1. Base to Collector: Reverse Bias
   
2. Base to Emitter: Reverse Bias
   

Example Circuit:

PNP Transistor

Symbol:     Layout:

This is an exact opposite of NPN Transistor. When we check it using Multimeter by keeping the Black Probe on the base and Red probe on either Collector or Emitter, we hear buzzer. This indicates the following:

1. Base to Collector: Forward Bias
   
2. Base to Emitter: Forward Bias
   

When do this in reverse order, we do not hear buzzer. This indicates the following:

1. Base to Collector: Reverse Bias
   
2. Base to Emitter: Reverse Bias
   

Example Circuit:

I.C. Integrated Circuits

Integrated Circuits have many inbuilt components in it and it is designed as per the circuit requirements. There are 2 types of I.C.

1. PGA (Pin Grid Architecture)
   
2. BGA (Ball Grid Architecture)
   

All the major sections in the Electronic devices are controlled by IC’s. For Example,Mobile’s Charging, Power, Network, Audio sections etc.

Most of the faults in the electronic devices are because of IC’s. They have most of the load on them.

Soldering Techinques

Soldering is a process of making and breaking the soldering contacts of the electronic components. It is done by the equipment called as Soldering Iron. There are two types of soldering irons:

1. 25 Watt High Power AC Iron
   
2. Micro Tip DC Iron
   

Accessories Required for Soldering:

1. Solder Wire (Trip 60/40 i.e. 60% Aluminium and 40% Tin)
   
2. Liquid Soldering Paste / Soldering Flux