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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 microphone is still used for your outgoing messages and these electrical signals are digitized as well as the incoming signal message on your phone line. These analog speech signals go to an analog-to-digital converter (ADC). The ADC samples the ana- log signal at a very high rate and converts it into digital words. To recover the incom- ing and outgoing messages, the digitized data from the memory chip must go to the digital-to-analog converter (DAC) for you to hear the messages. After filtering from the DAC, the reconstructed synthesized voice is very near that of the original. These tapeless machines can have more features and are almost trouble-free, compared to the cassette answering machines. Some answering machine troubles and solutions To repair and clean the answering machine, take out the screws (Fig. 8-29) to remove the bottom of the case. Problem or symptom Machine will not answer an incoming call. Probable cause and correction Check the ring-detection circuit. Also check and clean the cord and module plugs from phone jack to the answering machine base. Figure 8-30 shows some zener diodes that are in series with the input phone line for protection. They might be defective because of lightning surges and could lower the ring voltage level. Use an ohmmeter to check these diodes. The problem could also be that too many phones are on one line, which can reduce the ring voltage level. HOW A PHONE ANSWERING MACHINE WORKS 279 FIGURE 8-26 The record/play head can be cleaned without removing the top case of the answering machine. 280 TELEPHONE AND ANSWERING MACHINE SYSTEMS FIGURE 8-27 A tapeless Memory chips CPU Microphone Speaker Voice amp. Voice amp. Relay driver DTMF decoder Ringer circuit & ring detector Ringer circuit Various button controls & readout displays Digitized speech network A/D + D/A converters Telco line Filter FIGURE 8-28 A block diagram of an all-electronic digital answering machine. or IC memory/digitized voice mail answering machine. Problem or symptom Cassette tape will not rewind. Probable cause and correction Check for a loose or broken belt from the motor to the hub spindle. Clean any dirt or grease from belts. Also, a broken or jammed gear could be the trouble. Check and clean any dirt or grease from the mechanical parts or rubber wheels. Problem or symptom New messages are being taped over all old messages. The message is not intelligible. Probable cause and correction The tape is not being erased between recording sessions. The erase head or its circuitry and wiring are usually at fault. Also, be sure that the erase and play/record heads are clean. Problem or symptom Tape will not move or moves erratically. Probable cause and correction You might have a broken tape or a damaged cassette. Re- move cassette and replace with a new one. Check gears and spindles to see if they turn freely or are jammed. If tape is broken and tangled check the capstan shaft and pinch roller and see if any tape has been wrapped around them. Remove any tape and clean these components. HOW A PHONE ANSWERING MACHINE WORKS 281 FIGURE 8-29 For cleaning and repair, remove four screws from bottom of the machine. Problem or symptom No dial tone. Probable cause and correction Check all phone cords and module plugs. Check hook (receiver hang-up) switch for proper movement. Problem or symptom The message indicator flashes, but no message is recorded. Probable cause and correction Replace the cassette tape with a new one and record another message. Clean the record/play heads. Problem or symptom Loss of memory modes. Probable cause and correction The small battery (Fig. 8-31) could be worn out. This battery usually plugs into a slot on the bottom of the machine and should be replaced. If the bat- tery has become corroded, the connectors should be cleaned. Take the case off of the machine and clean it with a brush and solvent (Fig. 8-32). 282 TELEPHONE AND ANSWERING MACHINE SYSTEMS FIGURE 8-30 These zener diodes might be faulty and cause the ring-detection circuit not to function, and the machine will not answer or record calls. HOW A PHONE ANSWERING MACHINE WORKS 283 FIGURE 8-31 The small, thin battery used for chip memory is shown being FIGURE 8-32 Battery terminals being cleaned with a soft brush and solvent. replaced. Problem or symptom The answering machine will not function. It beeps and the call- counter LED flashes. Probable cause and correction Machine has locked because of a loss of ac line voltage, surge, spikes, etc. Unplug the power block from the ac outlet for 20 seconds, then plug back in. This will reset or reboot the microprocessor (URT) within the answering machine. Problem or symptom The message sound level is too low. Probable cause and correction Check the setting of the volume control. Check and clean the play/record head and capstan. Cordless Telephone Overview The sales of cordless phones probably account for over half of all telephone sales. These phones set you free to roam around room-to-room, all over your home and even outside in the yard and workshop, etc. SOME CORDLESS PHONE CONSIDERATIONS Some portions of the cordless and conventional corded phones have the same operations. They both convert the sound of a voice into electrical signals and transmit them via tele- phone lines to another telephone receiving set. At the same time, the telephone converts these electrical signals of the person’s voice “at the other phone” back into sound waves. Of course, the big physical difference with the cordless phone is that there is no cord between the handset and phone base. With a conventional phone, the electrical impulses are carried by the cord between the handset and the phone base; then they are sent out over the telephone lines. However, with a cordless phone, the electrical signals travel between the handset and telephone base via radio waves. The cord from handset to base has been replaced by a two-radio, which has duplex opera- tion and allows two conversations simultaneously. A simple cordless phone drawing is shown in Fig. 8-33. As with two-way radios, auto radios, and CB radios, the reception and interference can vary from location to location and from time to time. These same kinds of problems can be a factor with many cordless phones. This could be bothersome because we have all expected very clear reception over the fine telephone systems. Americans now expect phone pri- vacy, excellent sound quality and high reliability. Some cordless phone problems Poor sound quality Some phones might have poor audio response, receive interference from electrical devices and interference from other cordless phones close by. Short range The main appeal of a cordless phone is the ability to let you move around without pulling a cord. However, some phones have a very short range. 284 TELEPHONE AND ANSWERING MACHINE SYSTEMS Your phone use time is limited Because the cordless phone is powered by a battery in the handset, the phone might quit during a conversation because the battery needs to be charged. Also, most cordless phones will not work if the home power goes off. Conversation privacy Other people with a cordless phone on your frequency can lis- ten to your conversation if they are within range of your phone. However, the newer cordless phones, some in the 900-MHz band, offer digital transmission with encoded speech information and also automatic channel switching if someone transmits on your frequency. Cordless phone frequency bands The early model and some even sold today work on the 46- to 49-MHz radio-frequency band. This is a small region between the CB band and TV Channel 2. A new generation of cordless phones were developed in 1990 in the 900-MHz band. These phones operate at a much higher frequency (902 MHz to 928 MHz) and a greater transmitter output power. Phones operating at these higher frequencies have less interfer- ence and the band is not as crowded. Lucent Technologies (formerly AT&T) and Pana- sonic now have 900-MHz phones with a range of up to 4000 feet. Two transmission modes Not only do cordless phones operate in two frequency bands, but they have two different transmission modes to transmit and receive conversations. Early model phones used analog transmission, which is a continuous signal that varies in intensity like a radio broadcast station. An early model analog phone is shown in Fig. 8-34 photo. The latest 900-MHz phone technology uses digital transmission, which is a series of short, computer-coded signals that are decoded at the phone’s receiver. Digital phone transmission reduces the noisy, buzzing, and crackling usually found in cordless analog phones; also, they are harder for someone to eavesdrop on. CORDLESS TELEPHONE OVERVIEW 285 Antenna 46 to 49 MHz or 900MHz Hand unit holder Base unit Optional key pad Contacts to battery Transmitter microphone Touch pad Receiver speaker Portable phone hand unit FIGURE 8-33 Drawing of a basic cordless phone operation system. Digital phone modes The digital phone manufacturers use different ways to transmit their encoded narrow-band signal in the 900-MHz frequency range. Spread-spectrum cordless phones stretch (or spread) the narrow band signal over a multitude of different frequencies and are not as susceptible to interference. Spread-spectrum phones would be like many people talking identical messages all at the same time over the phone system. If one, or even quite a few, of these messages are blocked or interfered with, you would still receive the message from the others. Because the signals transmitted from these cordless phones are “spread out” over a wide bandwidth and with increased transmit power, these phones will have increased range and voice clarity. The 900-MHz phone (Fig. 8-35) has a range of more than one-half mile. SOME DIFFERENT PHONE TECHNOLOGIES Now look at some of the various cordless phone technologies that deal with clarity, pri- vacy, and range. In regard to call security, the new digital technology now makes it possi- ble to eliminate the eavesdropping problem. Some security codes now being used To keep outsiders from using your cordless phone, almost all phones sold today use some type of code between the handset and the 286 TELEPHONE AND ANSWERING MACHINE SYSTEMS FIGURE 8-34 This cordless phone uses analog RF signals with frequency modulation on frequencies allotted from 46 MHz to 50 MHz. phone base to prevent unauthorized use of your phone line by someone using another handset on your frequency. However, many phones don’t secure the call itself. Basic scrambling This is a basic way of scrambling a conversation so that it is more difficult to decipher, except by its own receiving set. Just about any competent electronics technician could unscramble this code. Digital encoding This one generates coded signals that are more difficult to decipher than a basic scrambling mode. Probably a competent electronics engineer could unscram- ble this coding and reconstruct the conversation. Spread-spectrum encoding This is the most difficult code to crack, having been devel- oped by the military for war applications. It would probably take a few years for a highly skilled communications engineer, with very specialized knowledge and very sophisticated equipment, to eventually bypass this security code. This spread-spectrum encoding goes by a trade name of Surelink Technology. CORDLESS TELEPHONE OVERVIEW 287 FIGURE 8-35 Young lady using a 900-MHz cordless phone. These phones can have a talk range of one-half mile or more. CORDLESS PHONE SOUND QUALITY The characteristics of these two phone frequency bands has a lot to do with the quality of re- ception. Cordless telephones in the 46- to 49-MHz range are much more prone to interfer- ence from a much more cluttered frequency band. This band is much more susceptible to electrical interference and other radio services. Cordless phone receivers in the 900-MHz band must be a lot closer to an interference source to be affected. Companding This system is somewhat like the Dolby stereo audio system. The system essentially “loudens” the transmission to overcome the naturally occurring hiss, then brings it down to normal levels at the receiving end. This technique goes by trade names of Sound Charger and Compander. Multichannel capability Many cordless phones can operate over several channels. When you hear some interference, you can manually switch to another channel. However, some automatically move to another channel, looking for a channel with less interference. Because of the limited space between channels in the 46- to 49-MHz range, this technology is not very effective for these cordless phones. In the present FCC frequency band allot- ment, the number of channels is limited to 25 for low-band phones, 40 for high-band stan- dard, and digital cordless phones have the equivalent of 100 high-band spread-spectrum channels. Digital transmission This transmission involves sending the message as a series of computer codes. Because each bit of code only has a designated value of “1” or “0,” unlike analog radio transmissions that have infinite possibilities—the receiving set can more eas- ily identify the incoming code in the presence of interference. However, if there is signifi- cant interference, the conversation might sound “choppy” because an entire code is lost. Spread-spectrum transmission The radio transmission technique also uses a series of computer codes. However, because the same signal is stretched out over a broad frequency band, the likelihood of “choppy” conversations is considerably eliminated. A receiver only needs to receive a part of the transmitted signal to reconstruct the original message. Spread-spectrum transmission will retain its quality—even if the 900-MHz frequency becomes more crowded. Digital spread-spectrum cordless phones often display the Surelink tech- nology label. Cordless telephone range Range is a key characteristic of the cordless telephone—regard- less if it operates in the low or high radio band and whether it is analog or digital. Different cordless phones transmit various levels of power, much the way radio stations use different levels of power output. Higher-powered cordless phones can transmit signals over greater dis- tances. However, the phone also needs more battery power to do this. This will require larger batteries or a shorter use time. Spread-spectrum cordless phones get additional range at lower power levels because they use battery power more efficiently than nonspread-spectrum phones. The FCC also allows the spread-spectrum phones to operate at higher transmit power levels than conventional phones. Analog phones These phone systems have the shortest range and are the most likely to be affected by high buildings, hills, etc. These analog cordless phones, operating in the crowded low band, are restricted by the FCC to no more than 0.04 milliwatts of radiated power, and rarely exceed 500 feet of working range. Standard digital phones The inherent characteristics of this mode of transmission, plus the fact that they typically transmit in the 900-MHz band, increases their range up to 0.25 mile. The FCC limits the power output of these phones to no more than 0.75 mW. 288 TELEPHONE AND ANSWERING MACHINE SYSTEMS [...]... conversations Figure 8-52 illustrates how area A and area B are divided up in cells of different channel numbers and frequencies to avoid radio interference When a cell phone customer initiates a call, the closest cell site then automatically opens up two unused channels to complete the call HOW THE CELL PHONE OPERATES The cellular phone packs a lot of sophisticated electronic components into a very small... remote-control hand unit used to control older-model TV sets 314 HOW REMOTE-CONTROL SYSTEMS WORK a universal remote can be reprogrammed for many different kinds of devices and multipurpose remote control units are also supplied with many TVs and VCRs A block diagram of an infrared digital remote-control transmitter is shown in Fig 9-4 Figure 9-5 shows the infrared remote receiver located within a TV, VCR,... operation is a highly sophisticated/complicated electronics system that has evolved over many years of development and huge investments of many communications companies Now look at a basic cell phone system’s unique operations The cell phone concept has very little resemblance to a conventional two-way radio communications or repeater system Figure 8-51 illustrates how a regional cell network is laid out The... phone switch equipment office Cell Tx & Rx site Telco land lines FIGURE 8-51 Cell Drawing of how regional cell system sites are laid out MOBILE RADIO TELEPHONE COMMUNICATIONS 303 Cell coverage area B Cell coverage area A Cell channel numbers 510 76 48 54 620 520 562 532 27 265 72 272 551 185 78 190 FIGURE 8-52 How cell phone channel numbers are allocated and laid out for a typical wireless phone system... antennas are just screwed on or off (Fig 8-46) Most electronics stores will probably have a replacement for your model phone Also, if you cannot get your cordless phone operating, Radio Shack has a repair service for most all brands of cordless phones Phone surge protection A phone surge- and spike-protection module that plugs into an ac outlet is shown in Fig 8-47 These units can protect any type phone... is it a two-way radio, but a computer and telephone And some cell devices have an answering machine and a pager To repair them, you need to be a highly trained electronics technician and have very specialized and expensive test instruments However, later in this chapter, some repair tips are listed that you can check on before calling on a professional service center Transmit/receive section In Fig... up e-mail messages; however, typing long messages is a little slow and tough with these “itty-bitty keys.” The PocketNet Phone will let you track UPS and FedEx packages or send e-mail to a Fax machine At this writing, the PocketNet Phone is now up and running in quite a few markets I have found it does not always work in certain areas and does not always operate very well indoors However, these problems... laptop computer, and lots of memory for phone numbers, etc However, the small screens are tough to read Also, with these smart ones you can send and receive e-mail while on the run The three models I have used are the Kyocera model QCP 6035, the Samsung model SPH-1300, and the Handspring Treo model 180 Let’s now take a look at the Treo-180, shown in Fig 8-56 The Treo is a pretty small, rugged device... in Fig 8-58 while taking on-the-air music requests for CD selections FIGURE 8-58 A busy DJ using two cell phones to keep the music going This page intentionally left blank 9 HOW REMOTE-CONTROL SYSTEMS WORK CONTENTS AT A GLANCE How Remote-Control Systems Work The ultrasonic remote transmitter The infrared (IR) remote-control transmitter Universal remote-control device Intelligent remote-control system... change channels These early model remotes produced only four to eight analog frequencies Some later-model 311 312 HOW REMOTE-CONTROL SYSTEMS WORK Magnavox remotes generated ultrasonic control pulses and would have 10 or more remote control functions Some modern-day remote controls are shown in Figs 9-1 and 9-2 Remote units now control TVs, VCRs, camcorders, stereo audio units, cable TV converter boxes, . that too many phones are on one line, which can reduce the ring voltage level. HOW A PHONE ANSWERING MACHINE WORKS 279 FIGURE 8-26 The record/play head can be cleaned without removing the top case. and the machine will not answer or record calls. HOW A PHONE ANSWERING MACHINE WORKS 283 FIGURE 8-31 The small, thin battery used for chip memory is shown being FIGURE 8-32 Battery terminals being. competent electronics technician could unscramble this code. Digital encoding This one generates coded signals that are more difficult to decipher than a basic scrambling mode. Probably a competent electronics