JBL Decade L36 - Page 17

If the previously non-functional loudspeaker system
operates, the amplifier or one of the component program
sources (tuner, phono, tape deck, etc.) is malfunctioning.
In the event that the suspect loudspeaker system is
still inoperative, it is probably defective.
To determine whether the defect lies in the amplifier
or in one of the component program sources (after
verifying that the loudspeaker systems are not defective)
reverse the right and left cables from the program source
at the amplifier. If the original channel is still
inoperative, the amplifier is defective; if the previously
inoperative channel functions, the program source is
defective. If the amplifier is not faulty, alternately check
each program source until the defective unit has been
isolated. It is unlikely that more than one program
source will be faulty at any given time.
Extraneous interference such as static or radio
broadcast signals can be picked up by the component
devices. When this occurs, the troublesome unit can
be identified by disconnecting inputs from the
receiver or amplifier until the interference stops. Again,
if the interference persists with none of the input
devices operating through the power source, the receiver
or amplifier itself is probably defective. Shorting plugs,
available from your JBL Audio Specialist, should be
inserted in unused phono inputs to help eliminate
stray hum or signal pickup.
Fuzzy or indistinct high pitched sounds can usually
be traced to the recording itself, a defective cartridge,
a worn stylus or insufficient tracking force. Problems
with low frequency reproduction are usually the result
of room acoustics or placement of the speaker system.
Excessive bass boost or incorrect loudness compensation
tend to give a muddy or "boomy" quality to reproduced
music. The music system can be checked for turntable
rumble or other extraneous low frequency signals by
removing the loudspeaker grille assembly and observing
the motion of the low frequency cone while the system
is playing at high volume. If the cone continually
moves in and out more than V2 inch or so, excessive
low frequency power is being fed to the loudspeaker
system.
Hum may be caused by locating a turntable or tape
recorder directly over or underneath the amplifier or
receiver. The farther the audio power source is located
from the phonograph cartridge or tape heads, the less
chance there will be of picking up hum. The AC leads
and shielded cables should be as widely separated as
possible; AC lines should never cross cables or
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