Earphone Cords; Hum And Random Noise; Distortion And Frequency Shift; Section 3 - Routine Maintenance - Welch Allyn Grason-Stadler GSI 17 Series Service Manual

3.1 EARPHONE CORDS

With extended use, earphone cords tend to fray internally at
junctions with
fraying will ultimately either decrease the signal level in
associated
earphone or cause signals to be intermittent as
cord is flexed.
To check
for
control (F7) to 1000 or 2000 Hz, set HL control (F3) at a
comfortable audible level, press the Present Bar (F4)
earphone cord
intermittent signal,
sound superimposed over the signal that coincides
scratchy
flexing of the cord.
the
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
Some audible random noise at levels above 60 dB is
levels.
permissible. Below 60 d B however, only the signal should be
Any of these noises can be confused with the signal by
audible.
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
through
the GSI 17
frequencies at
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
If distortion is heard in one earphone but not in the
position.
other, the chances are high that the earphone is at fault and
should be replaced.
immediately scheduled for maintenance.
S E C T I O N
Routine Maintenance
both earphone and audiometer
either condition, set
next to plug at
abrupt changes in
The presence of any of
the earphones
a loud, but not uncomfortable, level (70 to 80
In any case, the audiometer should be
3
connectors.
the audiometer
both ends, listening
signal level, or a
while
presenting
the
This
the
the
frequency
and flex
for
with
these
three
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