SECTION 3
-
Routine Maintenance
3.1 EARPHONE CORDS
With extended use,earphone cords tend to fray internally at
the
junctions with
both earphone and audiometer
connectors. This
fraying
will ultimately either decrease the signal level in
the
associated
earphone or cause signals to be intermittent as
the
cord is flexed.
To
check
for
either condition, set
the
audiometer
frequency
control (F7) to 1000 or 2000 Hz, set HL control (F3) at a
comfortable audible level,
press the Present Bar (F4)
and
flex
earphone cord
next to plug at
both ends,
listening
for
intermittent
signal,
abrupt
changes in
signal
level, or a
scratchy
sound superimposed over the signal that coincides
with
the
flexing of the cord.
The presence of any of
these
three
conditions signifies that the cord should be replaced.
Repeat the test for the other earphone.
3.2 HUM AND RANDOM NOISE
This test can be made during the check for attenuator noise.
With the instrument set on 1000 Hz,
move the HL control (F2) from
0 to 60
dB
and listen for low-frequency hum (60 to 120 Hz) and
random noise (hiss or low rushing
sound) at all attenuator
levels.
Some audible random noise at levels above 60
dB
is
permissible.
Below 60
dB
however, only the signal should be
audible.
Any of these noises can be confused with the signal by
naive subjects and affect the accuracy of the audiogram.
Schedule the audiometer for immediate service if any of these
symptoms are detected.
3.3
DISTORTION AND FREQUENCY SHIFT
This check is most easily performed by listening to the output of
the
GSI 17
through
the
earphones
while
presenting
all 11
frequencies at
a loud,
but not uncomfortable, level (70 to 80
dBHL for normal ears).
Listen for rattling, rasping or distortion in the tones
presented.
Listen also to ascertain that signal frequencies
change when the Frequency Selector (F5) is moved to a new
position.
If distortion is heard in one earphone but not in the
other,
the chances are high that the earphone is at fault and
should be replaced. In any case,the audiometer should be
immediately scheduled for maintenance.
13
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