How electronic things work Electronic equipment ''on the blink''? Don''t junk it or pay sky-high repair costs - fix it yourself! Here''s a guide to understanding and repairing electronics equipment written for people who would ordinarily ''call the shop''. With this fully illustrated, simple-to-use guide, you will get a grasp of the workings of the electronics world that surrounds you - and even learn to make your own repairs. And you may even start enjoying it! Whether you want to pocket the savings on repair bills, give your beloved equipment the best possible care, or merely understand how it all works, this book will show you how in easy-to-understand language and clear illustrations - and you don''t need any technical experience. Written by a technician who has fixed virtually everything that plugs into a wall, this handy do-it-yourself introduction to home and office repair delivers: clear explanations of how things work, written in everyday language; easy-to-follow, illustrated instructions on using test equipment to diagnose problems; guidelines to help you decide for or against professional repair; tips on protecting your beloved equipment from lightning and other electrical damage; and, lubrication and maintenance suggestions. This is an ''Electronics 101'' for true beginners. Next time your equipment acts up, don''t get mad. Get it working - with a little help from this book. This book features how to understand (and fix): color TVs, DVDs, wireless cellular phones and PDAs, radios, speaker systems, audio/video tuners, CD players, monitors, camcorders, copiers, and fax machines.
A BRIDGE-TYPE POWER SUPPLY Bridge diode power supplies are used in many kinds of electronic equipment, such as TVs, video recorders, and stereo sound systems. The bridge circuit power supply is unique because it can produce a full-wave output without using a center-tapped transformer. The typical diamond-shaped diagram for this type power supply is shown in Fig. 1-42. You could think of the bridge-rectifier circuit as an electronic switching system. Think of the diode rectifiers as switching all of the positive ac pulses to the Bϩ line and all of the negative ac pulses to the B-line or to chassis ground. ELECTRONIC POWER SUPPLIES 29 Diode Filter capacitor Fuse ACLine T1 B+ Load FIGURE 1-40 A half-wave rectifier power-supply circuit. FIGURE 1-41 A full-wave rectifier power-supply circuit. Diodes Smoothing capacitors Choke Fuse ACLine T1 B+ Load C1 C2 THE VOLTAGE-DOUBLER POWER SUPPLY A voltage-doubler power supply can have a transformer or it can be direct ac-line operated. The transformerless type is used in equipment that requires a higher dc voltage output and also to reduce the cost and weight of the device. A basic transformerless doubler circuit is shown in Fig. 1-43. To see how it works, assume that the half-wave diode (X1) is connected to produce a positive voltage on the Bϩ line of 30 INTRODUCTION TO VERY BASIC ELECTRONICS “101” Diodes Capacitors Filter Fuse ACLine T1 B+ FIGURE 1-42 A typical bridge-rectifier power-supply circuit. Note the B+ B- X1 X2 Resisitor 120 vac Fuse + + 240 vdc AC line input FIGURE 1-43 A power-supply voltage-doubler circuit that does not use diamond shape of the diodes’ layout. a power transformer. 120 volts. Diode X2 is then added to the circuit, but is connected in the opposite polarity. This will make diode X2 –120 volts, with respect to ground. This will “add,” then produce a voltage of approximately 240 volts between the B+ and B– points. The problem with this power supply is that the B– is connected to the chassis of the device. This makes it a “hot” chassis, which will create a shock hazard. When you take the case or cover off of this type of equipment, always be cautious and you should plug the device into an isolation trans- former. Common power-supply problems are blown fuses, shorted diodes, burnt resistors, and open or shorted filter capacitors. Use your volt/ohm meter to check out the power-supply faults. A digital multimeter is being used in Fig. 1-44. You will find more power-supply information and circuits plus troubleshooting tips in other chapters of this book. ELECTRONIC POWER SUPPLIES 31 FIGURE 1-44 A digital multimeter is being used to check a “block-type” plug-in power supply. Electronic Circuit Soldering Techniques When removing or replacing parts on a PC board, you will need a soldering iron (20 to 25 watts), rosin “flux” or solder with a rosin core. A solder wick, which is a flat-braided copper strips is a useful aid for soaking-up solder when removing a part from the PC board. Figure 1-45 illustrates how the solder wick is used to remove solder from a part on the PC board. Figure 1-46 shows two types of soldering irons. The top one is a 25 watt and should be used for all PC board soldering. The larger 45-watt iron is used for soldering chassis grounds and large-wire connector lugs. Figure 1-47 is of a soldering gun and it only heats when the trigger switch is pulled on. These guns will heat up in about five seconds and usually are high wattage. They should not be used for soldering on PC boards because you can damage one very quickly. Many of these guns are rated a 100 to 150 watts. Figure 1-48 shows how a small iron is used to solder in the pins of an IC. ICs can be directly soldered onto the PC board or they might have a socket mounted onto the PC board and the chip will plug into the socket. In Fig. 1-49, an IC is being removed from its socket. Very carefully pry up each end of the IC, a little each time, so as not to bend or damage the pins. When installing the IC, be sure that the pins are straight and are lined up with the socket pin holders. Also, be sure the key or notch is correctly lined up with that marked on the PC board. A chip put in backwards can be very costly. Be cautious and recheck position of the chip key. 32 INTRODUCTION TO VERY BASIC ELECTRONICS “101” FIGURE 1-45 Solder wick being used to “suck up” solder from a connection on a PC board. ELECTRONIC CIRCUIT SOLDERING TECHNIQUES 33 FIGURE 1-46 A 25-watt (bottom) and a 45-watt soldering iron. FIGURE 1-47 A fast-heating soldering gun. 34 INTRODUCTION TO VERY BASIC ELECTRONICS “101” FIGURE 1-48 A 25-watt iron being used to solder the pins of an IC mounted on FIGURE 1-49 An IC chip being removed from a plug-in socket located on a PC board. a PC board. SURFACE-MOUNTED DEVICES AND THEIR SOLDERING TECHNIQUES As surface-mounted devices (SMD) have evolved, the electronics industry have built SMD equivalents for most conventional electronic components. New electronic equip- ment contains SMD resistors, capacitors, diodes, transistors, and ICs. Even wire jumpers and 0-ohm resistors are used because they are more easily installed by automated assem- bly machines. During assembly, the SMD unit is lightly glued to the circuit board with the metallic contacts lying on the copper path, where a circuit connection is to be made. Wave solder- ing then is used to join all SMDs electrically and mechanically to the board. Some SMD basics On most circuit diagram, an SMD device has an M following its part number. The M represents for (metal-electrode face bonding), which is the process used in producing chips. Surface-mount components are available in various sizes and configurations, starting with large microprocessors, all the way down to single diode packages. Even single diodes and resistors are available in different sizes. Surface-mounted resistors A typical SMD resistor consists of a ceramic base with a film of resistive material on one surface. Refer to Fig. 1-50. Two electrodes are on the ends of the base, which is in contact with the resistance film. The contacts are used in making a solder connection to a PC board. The resistance of the device is determined by the amount of film material. SMD resistors are typically in the 1 ⁄4- to 1 ⁄8-watt range. The regular color code is not used on SMD resistors. Three numbers are usually printed on the film and give the same infor- mation as the color code. The first two numbers represent the first two significant numbers of its value. The third number represents the number of zeros. Surface-mounted capacitors Chip capacitors are fabricated with layers of resistance film, separated by layers of a ceramic base material, which is the dielectric. Notice Fig. 1-51. ELECTRONIC CIRCUIT SOLDERING TECHNIQUES 35 Ceramic base ContactContact Resistance film *** FIGURE 1-50 A surface-mounted device (SMD) resistor. The chip capacitor is very similar in appearance to the resistor. The body generally has a two-digit or two-letter code to show the capacitance of the device. Surface-mounted diodes and transistors The SMD equivalent for solid-state devices are conventional silicon technology in new housings, again allowing for easier automated assembly. Refer to Fig. 1-52. The package for a diode is called an SMC (single-melt compo- nent). The diode is marked on one end with a band to denote the cathode of the device. The transistors are in packaging that corresponds to their purpose. The low-power device is in a SOT-23 (small-outline transistor) package. The transistors that function in heat- generating capacities are in a SOT-89 package that features a heatsink. The same packages are also used for FET and MOSFET devices. 36 INTRODUCTION TO VERY BASIC ELECTRONICS “101” ** Dielectric Plate film FIGURE 1-51 A surface-mounted device (SMD) capacitor. Cathode Anode Emitter Base Collector Heatsink (collector) EmitterBase Collector ** ** FIGURE 1-52 Drawings of SMD diode and transistor configurations. Integrated circuits The SMD integrated circuit, like the diode and transistor, is conven- tional technology repackaged for automated insertion, as well as miniaturization of the cir- cuit boards. The SOIC (small-outline IC) is similar to the standard DIP packaging, except that the legs are designed for surface-mount soldering. Note layout of SMD IC in Fig. 1-53. SMD-soldering techniques Soldering of and/or replacement of an SMD is different from a standard component in two ways. First, the reduced size of SMD components and circuit-board paths increase the need for care when repairing this type equipment. Sec- ondly, the tools required for repair are more specialized. Excessive heat can easily damage not only the SMD, but also the PC board paths. A controlled-heat soldering iron in the 20- to 25-watt range is a must. Small-diameter rosin-core solder is also needed. Solder wick is needed in different sizes and can be cut in short pieces. A bottle of flux should be used as an aid in heat transfer. Small-tipped tweezers and dental picks are useful in handling the SMD parts. A magnifier with a light source is very useful for close-up inspections. And a grounded soldering iron and tip should be used along with an anti-static wrist band to pre- vent damage to static-sensitive SMD components. Removing SMD resistors or capacitors In most cases, a SMD device is not reusable once it has been removed from the PC board. You should be sure that the device is defec- tive using troubleshooting techniques before removing a SMD. Now refer to Fig. 1-54. Add extra solder to the contact points to cause even solder flow. Grasp the component body with tweezers and gently rock back and forth while heating the solder on both ends. Remove the heat while continuing to rock the SMD contacts. Once leads are loose from the foil, quickly twist the SMD to break the epoxy or glue that was holding the SMD to the PC board. SMD transistor removal Refer to Fig. 1-55. Add solder to all three terminals. Grasp the component body with tweezers or needlenose pliers. Heat terminal C and rock the body up ELECTRONIC CIRCUIT SOLDERING TECHNIQUES 37 A A 1 A A Flatpack chip carrier Plastic leaded 1 FIGURE 1-53 Typical layouts of SMD ICs. until an open space exists between the terminal and pad. Now work on the other two ter- minals until loose. Removing SMD integrated circuits For IC removal, refer to Fig. 1-56. Apply solder liber- ally to all pins. Use a special soldering tip that will fit over the particular size of IC housing. This will allow all pins to heat up at the same time. Use a dental pick to lift the IC off as soon as the solder is molten. SMD parts replacement The replacement of any SMD follows a similar pattern. Be sure that the foil solder pads are free of any excess solder. Using short pieces of solder wick, clean 38 INTRODUCTION TO VERY BASIC ELECTRONICS “101” A B FIGURE 1-54 When installing an SMD, always add extra solder to all contact A B C FIGURE 1-55 Add solder to all three terminals when starting to remove an points for an even solder flow. SMD component. [...]... also very useful Figure 1-60 shows some of these basic electronic tools needed for repair work The following is a list of basic tools you should find useful for electronic repairs: I I I I Long-nose pliers Diagonal cutters Needle-nose pliers Long-nose pliers with side cutters 42 INTRODUCTION TO VERY BASIC ELECTRONICS “101” FIGURE 1-60 Some basic tools you will need for electronic equipment repairs... shows a camcorder PC board with several SMDs Electronic Test Meters (VOMs) A volt/ohm test meter is a “must have” if you want to troubleshoot and repair any electronic equipment These small, inexpensive meters can have an analog meter, which have a needle pointer that swings across the meter scale face plate, or a digital readout, which have the direct number readings on an LCD screen Figure 1-58 shows... Shack, Allied Radio, and MCM Electronics You can also order from TAB/McGraw-Hill Electronics Book Club Before you start working on your equipment with a problem you might want to make some notes and review the problem(s): I Notice when the problem occurs I Is the device cold or hot when the problem occurs? SOME SERVICE REPAIR TIPS I I I I 43 How does it perform or not perform? How often does it occur?... loud will the noise be masked and usually not heard However, tape noise is so much different from musical sounds that it sometimes can be heard even at these times How a Dolby recording is produced Let’s now see how the Dolby recording is made and what happens during tape playback The Dolby system “first” listens Before the tape recording is made, as shown in Fig 2-7, the Dolby system “listens” to the... to look for low voltage, no voltage, or too high of a voltage A small, easy to use, portable, battery-operated volt-ohm meter is shown Fig 1-59 Tools for Electronic Circuit Repairs Now for some information on some common small tools that are very useful for electrical and electronic circuit repairs Diagonal cutters, sometimes called side cutters or dikes, are used to cut wires and component leads They... occur? Is it intermittent? Have you had the electronic equipment repaired for the same symptoms before? Does it have to operate a long or short time before the trouble appears? Thus, as you see from this list, you need to note any type hint or clue to solve these mysterious electronic problems It helps if you are a good detective You will find that with most electronic equipment, such as CD players,... will become very bright or may blow the lamp should a circuit short occur In fact, over the years some electronic manufacturers have used pilot lights as fuses 46 INTRODUCTION TO VERY BASIC ELECTRONICS “101” Solder leads to pilot lamp socket and fuse Fuse ribbon open FIGURE 1-63 Illustration of how to make a pilot light test device to check on circuit current being drawn without blowing a lot of fuses... uninterruptible power supply (UPS) to plug in your more expensive electronic equipment Try to determine which part is faulty before replacing it, if at all possible You don’t want to start changing parts at random, also called shotgunning, like the fellow in Fig 1-64, to solve a circuit problem You now know what components make up various electronic devices and how they work You can now go onto the chapters of interest... adjust to various room arrangements and to your listening preference The Dolby recording technique First, see how an ordinary standard audio recording is produced Figure 2-4 illustrates how music consists of different loudnesses, separated by intervals of silence Loud and soft sounds are shown here as long and short lines The music represented by this drawing starts loud and gradually becomes very... FIGURE 1-58 Some inexpensive digital volt-ohm meters that are very useful for electronic circuit repairs TOOLS FOR ELECTRONIC CIRCUIT REPAIRS 41 FIGURE 1-59 A small, easy-to-use, battery-operated, portable volt-ohm meter Some cost $45 to $85 is also used to check all of the other various dc voltage levels that are found in electronic equipment circuit boards You can use the multimeter to look for low . problem occurs? 42 INTRODUCTION TO VERY BASIC ELECTRONICS “101” FIGURE 1-60 Some basic tools you will need for electronic equipment repairs. ■ How does it perform or not perform? ■ How often does. diodes’ layout. a power transformer. 120 volts. Diode X2 is then added to the circuit, but is connected in the opposite polarity. This will make diode X2 – 120 volts, with respect to ground. This. “101” Diodes Capacitors Filter Fuse ACLine T1 B+ FIGURE 1- 42 A typical bridge-rectifier power-supply circuit. Note the B+ B- X1 X2 Resisitor 120 vac Fuse + + 24 0 vdc AC line input FIGURE 1-43 A power-supply