LESSON 01
INTRODUCTION: BASIC INFORMATION HOW CELLPHONE WORKS?
How Cell-phone Works?
As a basic Part of a Technician, It is fully advice that he/she must possess a basic knowledge of
what technology he or she comes up to.
Before we proceed further, please take a simple brief to enhanced your knowledge about the
Field of What we are going to discuss hereafter.... Now first come first we all ever wonder how
does the cell phone works?
have you ever wondered how a cell phone works? What makes it different from a regular phone?
what's inside of it and how do they created it? What do all those terms like PCS, GSM,
CDMA and TDMA mean?
To start with, one of the most interesting things about a cell phone is that it is actually a radio --
an extremely sophisticated radio, but a radio nonetheless. The telephone was invented by
Alexander Graham Bell in 1876, and wireless communication can trace its roots to the invention
of the radio by Nikolai Tesla in the 1880s (formally presented in 1894 by a young Italian named
Guglielmo Marconi). It was only natural that these two great technologies would eventually be
combined.
If you prepare to take a deep knowledge, i recommended you to visit this site and have a brief
of Fundamentals of Wireless Communication
A basic technician all need is just to have a simple understanding about cellphones, we do not
need extreme and intimate deeper meaning about it, that's because what we are going to take
around here is to fix what those various mobile phones company created and build....to make it
as simple as that... We are going to fix somewhat if their product gets busted by the end user's
who bought it...
Below is just simple basic information I gathered to compensate somewhat of what we are going
to learn.
Cell Phone Network Technologies:
2G Technology
There are three common technologies used by 2G cell-phone networks for transmitting information:
* Frequency division multiple access (FDMA)
* Time division multiple access (TDMA)
* Code division multiple access (CDMA)
Although these technologies sound very intimidating, you can get a good sense of how they work just by breaking
down the title of each one.
The first word tells you what the access method is. The second word, division, lets you know that it splits calls based
on that access method.
* FDMA puts each call on a separate frequency.
* TDMA assigns each call a certain portion of time on a designated frequency.
* CDMA gives a unique code to each call and spreads it over the available frequencies.
The last part of each name is multiple access. This simply means that more than one user can utilize each cell.
FDMA
FDMA separates the spectrum into distinct voice channels by splitting it into uniform chunks of bandwidth. To better
understand FDMA, think of radio stations: Each station sends its signal at a different frequency within
the available band. FDMA is used mainly for analog transmission. While it is certainly capable of carrying digital
information, FDMA is not considered to be an efficient method for digital transmission.
In FDMA, each phone uses a different frequency.
TDMA
TDMA is the access method used by the Electronics Industry Alliance and the Telecommunications Industry
Association for Interim Standard 54 (IS-54) and Interim Standard 136 (IS-136). Using TDMA, a narrow band that is 30
kHz wide and 6.7 milliseconds long is split time-wise into three time slots.
Narrow band means "channels" in the traditional sense. Each conversation gets the radio for one-third of the time.
This is possible because voice data that has been converted to digital information is compressedso that it takes up
significantly less transmission space. Therefore, TDMA has three times the capacity of an analog system using the
same number of channels. TDMA systems operate in either the 800-MHz (IS-54) or 1900-MHz (IS-136) frequency
bands.
TDMA splits a frequency into time slots.
Unlocking Your GSM Phone
Any GSM phone can work with any SIM card, but some service providers "lock" the phone so that it will only work
with their service. If your phone is locked, you can't use it with any other service provider, whether locally or
overseas. You can unlock the phone using a special code -- but it's unlikely your service provider will give it to you.
There are Web sites that will give you the unlock code, some for a small fee, some for free.
GSM
TDMA is also used as the access technology for Global System for Mobile communications (GSM). However,
GSM implements TDMA in a somewhat different and incompatible way from IS-136. Think of GSM and IS-136 as two
different operating systems that work on the same processor, like Windows and Linux both working on an Intel
Pentium III. GSM systems use encryption to make phone calls more secure. GSM operates in the 900-MHz and
1800-MHz bands in Europe and Asia and in the 850-MHz and 1900-MHz (sometimes referred to as 1.9-GHz) band in
the United States. It is used in digital cellular and PCS-based systems. GSM is also the basis for Integrated Digital
Enhanced Network (IDEN), a popular system introduced by Motorola and used by Nextel.
GSM is the international standard in Europe, Australia and much of Asia and Africa. In covered areas, cell-phone
users can buy one phone that will work anywhere where the standard is supported. To connect to the specific service
providers in these different countries, GSM users simply switch subscriber identification module (SIM) cards. SIM
cards are small removable disks that slip in and out of GSM cell phones. They store all the connection data and
identification numbers you need to access a particular wireless service provider.
Unfortunately, the 850MHz/1900-MHz GSM phones used in the United States are not compatible with the
international system. If you live in the United States and need to have cell-phone access when you're overseas, you
can either buy a tri-band or quad-band GSM phone and use it both at home and when traveling or just buy a GSM
900MHz/1800MHz cell phone for traveling. You can get 900MHz/1800MHz GSM phones from Planet Omni,
an online electronics firm based in California. They offer a wide selection of Nokia, Motorola and Ericsson GSM
phones. They don't sell international SIM cards, however. You can pick up prepaid SIM cards for a wide range
of countries at Telestial.com.
CDMA
CDMA takes an entirely different approach from TDMA. CDMA, after digitizing data, spreads it out over the
entire available bandwidth. Multiple calls are overlaid on each other on the channel, with each assigned a unique
sequence code. CDMA is a form of spread spectrum, which simply means that data is sent in small pieces over a
number of the discrete frequencies available for use at any time in the specified range.
In CDMA, each phone's data has a unique code.
All of the users transmit in the same wide-band chunk of spectrum. Each user's signal is spread over the entire
bandwidth by a unique spreading code. At the receiver, that same unique code is used to recover the signal. Because
CDMA systems need to put an accurate time-stamp on each piece of a signal, it references the GPS system for this
information. Between eight and 10 separate calls can be carried in the same channel space as one
analog AMPS call. CDMA technology is the basis for Interim Standard 95 (IS-95) and operates in both the 800-MHz
and 1900-MHz frequency bands.
Ideally, TDMA and CDMA are transparent to each other. In practice, high-power CDMA signals raise the noise floor
for TDMA receivers, and high-power TDMA signals can cause overloading and jamming of CDMA receivers.
2G is a cell phone network protocol. Click here to learn about network protocols for Smartphones.
Now let's look at the distinction between multiple-band and multiple-mode technologies.
Multi-band vs. Multi-mode Cell Phones
Dual Band vs. Dual Mode
If you travel a lot, you will probably want to look for phones that offer multiple bands, multiple modes or both. Let's
take a look at each of these options:
* Multiple band - A phone that has multiple-band capability can switch frequencies. For example, a dual-band
TDMA phone could use TDMA services in either an 800-MHz or a 1900-MHz system. A quad-band GSM phone could
use GSM service in the 850-MHz, 900-MHz, 1800-MHz or 1900-MHz band.
* Multiple mode - In cell phones, "mode" refers to the type of transmission technology used. So, a phone that
supported AMPS and TDMA could switch back and forth as needed. It's important that one of the modes is AMPS --
this gives you analog service if you are in an area that doesn't have digital support.
* Multiple band/Multiple mode - The best of both worlds allows you to switch between frequency bands and
transmission modes as needed.
Cellular vs. PCS
Personal Communications Services (PCS) is a wireless phone service very similar to cellular phone service, but with
an emphasis on personal service and extended mobility. The term "PCS" is often used in place of "digital cellular,"
but true PCS means that other services like paging, caller ID and e-mail are bundled into the service.
While cellular was originally created for use in cars, PCS was designed from the ground up for greater user mobility.
PCS has smaller cells and therefore requires a larger number of antennas to cover a geographic area. PCS phones
use frequencies between 1.85 and 1.99 GHz (1850 MHz to 1990 MHz).
Technically, cellular systems in the United States operate in the 824-MHz to 894-MHz frequency bands; PCS
operates in the 1850-MHz to 1990-MHz bands. And while it is based on TDMA, PCS has 200-kHz channel spacing
and eight time slots instead of the typical 30-kHz channel spacing and three time slots found in digital cellular.
Changing bands or modes is done automatically by phones that support these options. Usually the phone will have a
default option set, such as 1900-MHz TDMA, and will try to connect at that frequency with that technology first. If it
supports dual bands, it will switch to 800 MHz if it cannot connect at 1900 MHz. And if the phone supports more than
one mode, it will try the digital mode(s) first, then switch to analog.
You can find both dual-mode and tri-mode phones. The term "tri-mode" can be deceptive. It may mean that the
phone supports two digital technologies, such as CDMA and TDMA, as well as analog. In that case, it is a true tri-
mode phone. But it can also mean that it supports one digital technology in two bands and also offers analog support.
A popular version of the tri-mode type of phone for people who do a lot of international traveling has GSM service in
the 900-MHz band for Europe and Asia and the 1900-MHz band for the United States, in addition to the analog
service. Technically, this is a dual-mode phone, and one of those modes (GSM) supports two bands.
3G and 3GS Technology
In the next section, we'll take a look at 3G mobile-phone technology.
3G technology is the latest in mobile communications. 3G stands for "third generation" -- this makes analog cellular
technology generation one and digital/PCS generation two. 3G technology is intended for the true multimedia cell
phone -- typically called smartphones -- and features increased bandwidth and transfer rates to accommodate Web-
based applications and phone-based audio and video files.
3G comprises several cellular access technologies. The three most common ones as of 2005 are:
* CDMA2000 - based on 2G Code Division Multiple Access (see Cellular Access Technologies)
* WCDMA (UMTS) - Wideband Code Division Multiple Access
* TD-SCDMA - Time-division Synchronous Code-division Multiple Access
3G networks have potential transfer speeds of up to 3 Mbps (about 15 seconds to download a 3-minute MP3 song).
For comparison, the fastest 2G phones can achieve up to 144Kbps (about 8 minutes to download a 3-minute song).
3G's high data rates are ideal for downloading information from the Internet and sending and receiving large,
multimedia files. 3G phones are like mini-laptops and can accommodate broadband applications like video
conferencing, receiving streaming video from the Web, sending and receiving faxes and instantly downloading e-mail
messages with attachments.
3GS feels wonderfully familiar – it’s design is almost identical to the 3G, and it’s not until you switch the device on that
you start to appreciate the differences. The “S” stands for speed – Apple has used a faster processor in the 3GS, and
the impact is immediate, with applications loading more briskly, programs running noticeably faster, and the already
slick user-interface getting an extra layer of go-faster stripes. It’s also HSDPA compatible, a step up from 3G,
meaning it can surf the web at faster speeds. Battery life is longer too; I was able to squeeze a full day out of my
iPhone without needing to give it a lunchtime charging boost.
LEARNING WITH BLOCK DIAGRAM ON HOW BASICALLY CELL-PHONE
WORKS?
How basically Cell-phone works?
In this lesson we are going to take a brief familiarization of a typical block diagram of a
cellphone. Block Diagram can help us understand the flow of a certain part of a cellphone's
circuit. A Cell-phone handset is basically composed of two sections,
which is RF and Baseband Sections.
RF
RF refers to radio frequency, the mode of communication for wireless technologies of all kinds,
including cordless phones, radar, ham radio, GPS, and radio and television broadcasts. RF
technology is so much a part of our lives we scarcely notice it for its ubiquity. From baby
monitors to cell phones, Bluetooth® to remote control toys, RF waves are all around us. RF
waves are electromagnetic waves which propagate at the speed of light, or 186,000 miles per
second (300,000 km/s). The frequencies of RF waves, however, are slower than those of visible
light, making RF waves invisible to the human eye.
Baseband
In signal processing, baseband describes signals and systems whose range of frequencies is
measured from zero to a maximum bandwidth or highest signal frequency. It is sometimes used
as a noun for a band of frequencies starting at zero.
In telecommunications, it is the frequency range occupied by a message signal prior to
modulation.
It can be considered as a synonym to low-pass.
Baseband is also sometimes used as a general term for part of the physical components of a
wireless communications product. Typically, it includes the control circuitry (microprocessor),
the power supply, and amplifiers.
A baseband processor is an IC that is mainly used in a mobile phone to process communication
functions.
Basically Baseband also composed of to sections which is the Analog and Digital Processing
Sections. So, we are going to separate each other for better and easier to understand.
Cell-phone have three different sections which is the following.
I prepare this to be simple and easy instead of using or explaining it with deep technical terms .
In this manner, it is easy for us to understand the concepts and methods of how basically the
cellphone works.
Cell-phone have three sections since baseband is differentiated by into two which is the Analog
and Digital function while the RF section remains as a whole circuit section.. which is the
following cosists.
1. Radio Frequency (RF Section)
2. The Analog Baseband Processor
3. And the Digital Baseband Processor.
Radio Frequency Processing Section
The RF section is the part of the cell-phone circuit is also known as RF Transceiver.
It is the section that transmit and receive certain frequency to a network and synchronize to other
phone.
The RF - A radio section is based on two main Circuits.
1 Transmitter
2 Reciever
A simple mobile phone uses these two circuits to correspond to an other mobile phone. A
Transmitter is a circuit or device which is used to transmit radio signals in the air.and a reciever
is simply like radios which are used to recieve transmissions(Radiation) which is spread in the
air by any transmitter on a specific frequency.
The two way communication is made possible by setting two transmitters and two recievers
sycronized in this form that a trasmitter in a cell phone is syncronised with the frequency of other
cell phone's recieving frequency same like the transmitter of second cell phone is syncronised
with the recieving frequency of first cell phone. So first cell phone transmits its radiation in the
air while the other phone listens it and same process is present in the opposit side. so these hand
held two cell phones correspond to one another.
the technology used in these days is a little bit different but it is based on the basic theory
prescribed before. the today's technology will be discussed in later on.
Analog Baseband Processor
A/D and D/A section
The analog baseband processing section is composed of different types of circuits.
This section converts and process the analog to digital (A/D) signals and digital to analog
signals (D/A).
Control section
This is the section acts as the controller of the the input and output of any analog and digital
signal.
Power Management
A power management section in mobile phones is designed to handle energy matters that is
consumed in mobile phones. There are two main sub sections in a single power section.
• Power Distribution and switching section
• Charging Section
A power distribution section is designed to distribute desired Voltages and currenst to the other
sections of a phone. this section takes power from a battery (which is figured commonly 3.6
Volts)and in some places it converts or step down to various volts like 2.8 V 1.8V 1.6V etc.while
on other place it also
steps up the voltage like 4.8 V. this section is commonly designed around a power IC(and
integrated circuit) which is used to distribute and regulate the voltage used in other components.
The Charging section is based on a charging IC which takes power from an external source and
gives it to battery to make it again power up when it is exhausted. this section uses convertibly
6.4 V from an external battery charger and regulates it to 5.8V wile giving it to battery. The
battery is made charged by this process and it is ready to use for the next session (a battery
session is a time which is provided by the manufacturer of a cell phone for standby by condition
of a mobile phone or talk condition.)
Audio Codecs Section
This section where analog and digital audio properties being process like the microphone,
earpiece speaker headset and ring-tones and also the vibrator circuits.
Digital Baseband Processor
This is the part where All Application being process. Digital Baseband Processor section is used
in mobile phones to handle data input and ouput signal like switching, driving applications
commands and memory accessing and executing.
These are the parts and sections o a Digital Baseband Circuit were installed.
CPU
CPU( Centeral Processing Unit) The Central Processing Unit (CPU) is responsible for
interpreting and executing most of the commands from the users interface. It is often called the
"brains" of the microprocessor, central processor, "the brains of the computer"
Flash and Memory Storage Circuits
*RAM( Random Access Memory)
*ROM,Flash(Read Only Memory
Interfaces such as the following were also part on this section:
*Blutooth
*Wi-fi
*Camera
*Screen Display
*Keypads
*USB
*SIM-Card
Here a typical overview of a block diagram on latest mobile phone designs.
Various mobile phones have different concepts and design on every aspects, but the methods and
operational flow are all exactly the same. It differs on how and what certain IC chips and parts
they are being used and installed to a certain mobile phone circuitry.
LESSON 02
Introduction To Basic Electronics
Definition of Electronics:
Electronics is the branch of science that deals with the study of flow and control of electrons (electricity) and the
study of their behavior and effects in vacuums, gases, and semiconductors, and with devices using such electrons.
This control of electrons is accomplished by devices that resist, carry, select, steer, switch, store, manipulate, and
exploit the electron.
Electronics isn't always easy, but you can learn. And you can do it without memorizing theories and formulas belong
in a Physics text. the focus of this program is learning how things work. Electronics may defined as an art of
knowledge to make such impossible things work. Things such as Televisions, AM/FM Radios, Computers and ob
course the mobile phones and etc. We are surrounded by electronics....
Learning how things work can be fun.
With this skill you can Build things.
make better use of things
and repair things..
have better job opportunities
An important part of learning electronics
is the the need to visualize the action inside a piece of equipment. In electronics things happen at a sub-atomic level.
to understand what is happening, you need a mental picture, a visualization of events you can see directly. You need
a in your mind of how events are turned on and off. you need to visualize signals being amplified and attenuated.
( These are long words for being made bigger and smaller )
take an overview of electronic equipment. Inside anything what's happening can be describe as some kind of source
delivering power to some kind of a load. The terms source and load become clearer as you can discover a few
basics. A source is where the energy comes from. A load is what does the work. When power is delivered to a load,
the load produces sound, heat, pictures or anything else that can be produced electronically..
Dow load this Tutorial Software below, In this program you will learn some useful hints about basic electronics, the
program includes some exercises to have fun with....
On successful completion of this lesson you will be able to:
describe the structure of a simple atom
recognize a series resistor circuit
calculate the expected current in a series circuit
calculate the power dissipated in a resistor from color code
measure the voltage across a resistor or circuit
measure the current through a resistor circuit
recognize several types of switches
determine circuit paths in switched circuits
LESSON 03
CELLHONE REPAIR TOOLS AND TEST EQUIPMENTS
Preparing the Proper Tools For Repairing..
There are many different variety and Cellphone Repair Tools. A lot companies offers online purchasing for such
certain tools for beginning into business... You can choose which is which for such certain product.
In my opinion, when you are into a planning to purchased any tools, Ask some experts first for that certain products
you are going to buy...
Basically these are the primary tools when you are going to repair cellphones.
1. Multi-Tester ( Analog/Digital)- Used to measure Voltages, Currents and Resistance in electronic components.
2. Screwdrivers - Used to loosen the phones screws.
3. Tweezers - used to hold and pick small cellphone component parts.
4. Soldering iron - used to solder / resolder electronic parts.
5. Soldering lead - used to bonds Electronic components.
6. Soldering Flux and Paste - Used to tightened soldering quality.
7. BGA Rework station - Applied Heat to remove and replaced parts and IC chips.
8. Re balling Kits - Tools for re balling IC bumps, this composed of Stencil plates, Ball Leads and Spatula
9. DC Regulated Power Supply- Used to substitute battery voltage when working on hardaware troubleshooting.
10. Flashing and Unlocking Device- it is Software Tools that used to unlock and flash mobile phones
programmable circuits.
11. Cables and Wires - Used as an Interface from PC to cellphones when working on like flashing, unlocking
and jailbreaking.
Test Equipment
Electronic test equipment is specialized equipment which is used in the testing of electronics. It can be utilized in the
construction of prototypes and new products, and in maintenance and troubleshooting. A huge family of components
are included under the umbrella of electronic test equipment, ranging from simple equipment which is used for routine
home repair to sophisticated systems which are used exclusively by engineers. Many companies sell used electronic
test equipment, which is often far less costly than brand new products and just as useful.
All of the devices in the family of electronic test equipment are capable of providing some sort of information about an
electronic device or circuit. This information can vary from something simple, like whether or not current is flowing
through a circuit, to something complex, like whether or not the components of a motherboard are working properly.
Electronic test equipment may be passive, or it may emit an active signal and register a response, and it can provide
specific measurements, or more generic data.
Typically, electronic test equipment includes a way to interface with an item being tested, such as a probe or clip, and
a readout which provides information, ranging from a light which becomes illuminated when something is working
properly to a readout with measurements. Sophisticated equipment may hook up to a computer for the purpose of
performing diagnostics, with the equipment running several different tests at once and compiling the information in a
computer program. This type of electronic test equipment is often used in the development of new products, to
confirm that they are safe and to test their limits.
One of the simplest examples of electronic test equipment is a continuity tester, a device which many people may be
familiar with. A continuity tester is used to determine whether a circuit is open or closed. If the circuit is open, it
indicates a fault or ground, while if it is closed, it is working correctly. Continuity testers are often used to diagnose
home electrical problems, such as a suspected fault in an outlet.
More sophisticated equipment can measure current, resistance, voltage, capacitance, charge, and digital circuits.
Testgear, as electronic test equipment is sometimes known, may also combine multiple functions for convenience.
Electricians, phone repair men, and cable installers typically carry testgear for use in their work, and electronic test
equipment is also used by engineers, physicists, and numerous other researchers and inventors.
LESSON 04
SAFETY PROCEDURES AND PROPER HANDLING OF TOOLS AND TEST
EQUIPMENTS ON CELLPHONE REPAIR
Safety procedure and proper handling of tool is highly observed when working any electronic components to
avoid risk of unnecessary further damages whatever you are working at. These are the following thing that always to
remind when working any electronic components such as cellphones.
Antistatic Wrist Strap
Wear a Ground Strap.
Anti static wrist strap is used to avoid risk of electrostatic discharge from a human body to an electronic component
circuit.
An antistatic wrist strap, ESD wrist strap, or ground bracelet is an antistatic device used to prevent electrostatic
discharge (ESD) by safely grounding a person working on electronic equipment.
It consists of a stretchy band of fabric with fine conductive fibers woven into it. The fibers are usually made of carbon
or carbon-filled rubber, and the strap is bound with a stainless steel clasp or plate. They are usually used in
conjunction with an antistatic mat on the workbench, or a special static-dissipating plastic laminate on the workbench
surface.
Hand Gloves
You are not just protecting your hand from posibble burns or brushes. it also protect the cellphones from scratches
and possible electrostatic discharge. A cotton cloth made glove is essential to use.
Safety Handling with Rework and Soldering Stations
Rework and soldering Station is a hot surface devices and can cause fire instanly and extreme burns on skin when
unproperly handled.
Always Observe and Set it in proper heat and air flow amounts.
Secure a safe place on your table where the rework station is located. Avoid inplacing it that people may pass or
standing by especially kids.
Always shut it off when not in use and place unto the holder stand to avoid risk of fire and skin burns.
Safety Handling of a Multitester
a multitester may damaged easily when unproperly handled. always check ranges when checking voltages and
currents. The deplection yoke of the analog meter may be bust out when overdrive by a current to it.
Measuring Resistance
Set the multimeter to Ohms or Resistance (turn meter on if it has a separate power switch). Understand that
resistance and continuity are opposites. The multimeter measures resistance in ohms, it can not measure continuity.
When there is little resistance there is a great deal of continuity. Conversely, when there is a great deal of resistance,
there is little continuity. With this in mind, when we measure resistance we can make assumptions about continuity
based on the resistance values measured. Observe the meter indication. If the test leads are not in contact with
anything, the needle or pointer of an analog meter will be resting at the left most position. This is represents an
infinite amount of resistance, or an "open circuit"; it is also safe to say there is the no continuity, or path between the
black and red probes. Careful inspection of the dial should reveal the OHM scale. It is usually the top-most scale and
has values that are highest on the left of the dial (a sideways "8" for infinity) and gradually reduce to 0 on the right.
This is opposite of the other scales; they have the lowest values on the left and increase going right.
Mesuring Voltage Ac-DC
Set the meter for the highest range provided for AC or DC Volts. Many times, the voltage to be measured has a value
that is unknown. For this reason, the highest range possible is selected so that the meter circuitry and movement will
not be damaged by voltage greater than expected.
Measuring Current by Ampere
Set the meter to the highest AC or DC Amp range supported. If the circuit to be tested is AC but the meter will only
measure DC amps (or vice-versa), stop. The meter must be able to measure the same mode (AC or DC) Amps as
the voltage in the circuit, otherwise it will indicate 0.
Be aware that most multimeters will only measure extremely small amounts of current, in the uA and mA ranges. 1
uA is .000001 amp and 1 mA is .001 amp. These are values of current that flow only in the most delicate electronic
circuits, and are literally thousands (and even millions) of times smaller than values seen in the home and automotive
circuits that most homeowners would be interested testing. Just for reference, a typical 100W / 120V light bulb will
draw .833 Amps. This amount of current would likely damage the meter beyond repair. A "clamp-on" type ammeter
would be ideal for the typical homeowner requirements, and does not require opening the circuit to take
measurements (see below). If this meter were to be used to measure current through a 4700 ohm resistor across 9
Volts DC, it would be done as outlined below:
Safety Handling of a Power Supply
Power supply may also damaged and cause damaged to a component..
Always set it and determine the correct amount of Voltage range to avoid risk of blowing out any electronic parts.
Do not short the two alligator clips because the power supply will heat up and may busted out the protection fuse.
LESSON 05
