Welch Allyn Grason-Stadler GSI 17 1717-9700, Service Manual

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S E C T I O N 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 d B 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.