WhitakerAudio AM/FM Stereo Tuner 2012, Сборка и руководство пользователя

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9 Troubleshooting Guidelines
Even an audio device that has been carefully built can experience problems. When presented with
a problem, proceed in an orderly manner to trace it down. Many failures are simple to repair if
you stop and think about what’s happening. Looking over the schematic diagram for 10 to 15
minutes to consider the possible causes can save hours of trial-and-error troubleshooting. Never
rush through a troubleshooting job.
Stereo audio products offer the technician an added benefit in that the same problem rarely
manifests itself in both channels. As such, the technician has a “known good” circuit as a
reference.
When checking inside the unit, look for changes in the physical appearance of components.
An overheated resistor or leaky electrolytic capacitor may be the cause of the problem, or point to
the cause. Devices never fail without a reason. Try and piece together the sequence of events that
led to the problem. Then, the cause of the failure—not just the more obvious symptoms—will be
corrected. In high voltage power supplies, look for signs of loose connections and overheating.
Do not overlook the possibility of tube failure. Tubes can fail in unpredictable ways, and
substitution may be the only practical test.
Troubleshooting through the process of elimination can also be useful. This technique
involves isolating various portions of the circuit—one section at a time—until the defective
component is found.
Never touch anything inside the unit without first removing all ac power and discharging all
filter capacitors with a test lead to ground. Most plate power supplies include bleeder resistors to
drain-off the charge on the capacitor(s) in the circuit. However, some designs do not include this
safety feature. Be careful.
Analyze each planned test before it is conducted. Every test in the troubleshooting process
requires time, and so steps should be arranged to provide the greatest amount of information about
the problem.
9.1 Safety Considerations
Electrical safety is important when working with any type of electronic hardware. Because
vacuum tubes operate at high voltages and currents, safety is doubly important. The primary areas