FAULT DIAGNOSIS IN AUDIO SYSTEMS
Longitudinal sound systems are not difficult to service; the electronics are simple, and identical to those of audio cassette recorders. Hi-Fi audio stages are very similar indeed to those used for the luminance signal, with the same sorts of pre-/de-emphasis, modulator/ demodulator, switching and clipping circuits, and similar recording amplifier and head preamp designs. The servicing techniques for both
are similar, then, and the oscilloscope is the most valuable diagnostic tool here; test cassettes are available from videorecorder manufacturers with Hi-Fi audio test signals recorded to factory-model specifications. For PCM audio systems much diagnostic work can be done by examining key test points for the presence or absence of waveforms and operating voltages. Analysis of the signals present in the digital sections, however, calls for very sophisticated test equipment which will rarely be found in an ordinary service workshop (see Chapter
22).