The document provides information about testing and repairing vehicle audio systems, including how AM and FM radio works, testing speaker polarity and impedance matching, diagnosing antennas, and types of speakers and crossovers. It explains that AM radio uses amplitude modulation while FM uses frequency modulation to transmit sound waves. Crossovers separate frequencies to send highs to tweeters and lows to woofers. Speaker polarity and impedance must match for best sound quality.
9. Figure 47–1 Audio systems use both electromagnetic radio waves and sound waves to reproduce sound inside the vehicle. Continued
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16. Figure 47–5 Using upper and lower sidebands allows stereo to be broadcast. The receiver separates the signals to provide left and right channels. Continued
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21. Figure 47–6 The five types of antennas used on General Motors vehicles include the slot antenna, fixed-mast antenna, rear-window defogger grid antenna, a powered mast antenna, and an integrated antenna. Continued
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23. Figure 47–7 The ground plane is actually one-half of the antenna.
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30. Figure 47–11 Between 6 and 7 volts is applied to each speaker terminal and the audio amplifier increases the voltage on one terminal and at the same time decreases the voltage on the other terminal causing the speaker cone to move. The moving cone then moves air causing sound. Continued (a) (b)
31. Figure 47–12 A typical automotive speaker with two terminals. The polarity of the speakers can be identified by looking at the wiring diagram in the service manual or by using a 1 1/2-volt battery to check. Continued
32. Figure 47–13 A speaker polarity tester can be easily constructed using a 1 1/2-volt battery. To test a speaker, connect the positive (+) lead of the battery to one speaker terminal and the negative (-) lead to the other speaker terminal for just a second and observe the direction the speaker cone moves. The positive (+) terminal of the speaker is the terminal that causes the speaker cone to move away from the magnet when touched with the positive (+) battery lead. Continued
33. Figure 47–14 (a) Two 4-ohm speakers connected in series result in a total impedance of 8 ohms. (b) Two 4-ohm speakers connected in parallel result in total impedance of 2 ohms. (b) Continued (a)
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36. A floating ground means that all audio components such as the receiver head, amplifier, and speakers share a common ground that is above and not connected to the chassis ground. This arrangement helps prevent interference and static that could occur if these components were connected to a chassis (vehicle) ground. If the components are chassis grounded, there may be a difference in the voltage potential (voltage); this condition is called a ground loop. What is a “Floating Ground”? CAUTION: Regardless of radio speaker connections used, never operate any radio without the speakers connected, or the speaker driver section of the radio may be damaged as a result of the open circuit.
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40. A bass blocker is a capacitor and coil assembly that effectively blocks low frequencies. A bass blocker is normally used to block low frequencies being sent to the smaller front speakers. Using a bass blocker allows the smaller front speakers to more efficiently reproduce the midrange and high-range frequency sound. What is a Bass Blocker?
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55. Figure 47–21 SDARS uses satellites and repeater stations to broadcast radio.
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58. ESN means electronic serial number. This is necessary information to know when reviewing satellite radio subscriptions. Each radio has its own unique ESN. What Does ESN Mean?
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63. Figure 47–26 A “sniffer” can be made from an old antenna lead-in cable by removing about 3 inches of the outer shielding from the end. Plug the lead-in cable into the antenna input of the radio and tune the radio to a weak station. Move the end of the antenna wire around the vehicle dash area. The sniffer is used to locate components that may not be properly shielded or grounded and can cause radio interference through the case (housing) of the radio itself.
65. A radio failed to work in a vehicle that was outside during a thunderstorm. The technician checked the fuses and verified that power was reaching the radio. Then the technician noticed the antenna. It had been struck by lightning. Obviously, the high voltage from the lightning strike traveled to the radio receiver and damaged the circuits. Both the radio and the antenna were replaced to correct the problem. Lightning Damage Figure 47–27 The tip of an antenna that was struck by lightning.
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