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Electrical/Electronic Auto Service Tech Tips
These Tech Tips are provided courtesy of autoclassroom.com, an online training resource for automotive instructors, students, and technicians.
Open is a four-letter word
An open in a circuit breaks the path for current flow. The open can be any break in the power side, load, or ground side of a circuit. A switch is often used to close and open a circuit to turn it on and off. Just remember:
open = no current flow
closed = current flow
Trying to locate an open circuit in a vehicle is often difficult and may cause the technician to use other four-letter words.
A capacitor makes an excellent sound system noise filter
Interference in a sound system or radio is usually caused by alternating current (AC) voltage created by a part in the vehicle such as the alternator (AC generator). By connecting a capacitor (also known as a condenser) to the power lead of the radio or sound system amplifier, the AC voltage passes through the capacitor to the ground where the other end of the capacitor is connected. Therefore, the capacitor provides a path for the AC without affecting the DC power circuit.
A cracked magnet becomes two magnets
Magnets are commonly used in vehicle crankshaft, camshaft, and wheel speed sensors. If a magnet is struck and cracks or breaks, the result is two smaller-strength magnets. Because the strength of the magnetic field is reduced, the sensor output voltage is also reduced. A typical problem occurs when a magnetic crankshaft sensor becomes cracked, resulting in a no-start condition. Sometimes the cracked sensor works well enough to start an engine that is cranking at normal speeds, but it will not work when the engine is cold.
Burn in to be sure
A common term heard in the electronic and computer industry is the term "burn in." "Burn in" means to operate an electronic device, such as a computer, for a period from several hours to several days. Most electronic devices fail in infancy, or during the first few hours of operation. This early failure occurs if there is a manufacturing defect, especially at the P-N junction of any semiconductor device. The junction will usually fail after only a few operating cycles. What does all of this information mean to the average person? If purchasing a personal or business computer, have the computer burned in before delivery. This step helps ensure that all of the circuits have survived infancy and that the chances of failure of a chip are greatly reduced. Display model sound or television equipment may be a good value, because during its operation as a display model, it has been burned in. The automotive service technician should be aware that if a replacement electronic device fails shortly after installation, the problem may be a case of early electronic failure.
Note: Whenever there is a failure of a replacement part, the technician should always check for excessive voltage to or heat around the problem component.
Electronic components do not like three (four) things
Computers are sensitive electronic devices that can be damaged if subjected to:
high voltage -- especially static electricity
high current (amperes) -- current through a computer circuit is usually limited to one ampere or less
high heat -- electronic devices work best when isolated from extreme heat
There is another item that may be of interest. While troubleshooting a computer-related problem, this author found the vehicle computer full of water due to a leaky windshield. So add another item to the list: Computers can't swim!
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