Bose FREESPACE BUSINESS Service Manual page 22

C. Connect a distortion meter across either the
left or right twiddler output terminals. The
distortion should be less than 3.0% THD.
D. Repeat the test for the other channel.
7. Air Leak Test
NOTE: This test can be performed with a fully
assembled module.
A. Connect an oscillator to the module's L/R
audio input terminals. Adjust the oscillator to 40
Hz,185 mVrms. Listen for air leaks around the
cabinet,edge of the amplifier panel,edge of the
heatsink,around the barrier strips (inside junction
box),tone control knobs,power switch, and panel
screws. If there is a"whooshing"noise,there is
probably an air leak in one of these
locations.Repair any air leaks as required.
8. Woofer Rub and Tick Test
NOTE: In order to perform this test,it is necess-
ary to access the woofer. Refer to Procedure
9,steps A. and B.,Woofer Removal,in the
Disassembly/Assembly Procedures section.
A. Connect an oscillator to the module's L/R
audio input terminals. Adjust the oscillator to 10
Hz,185 mVrms. No extraneous noises such as
rubbing,scraping or ticking should be heard.
NOTE: To distinguish between normal
suspension noise and rubs or ticks,displace the
cone on the woofer slightly with your fingers. If
the noise can be made to go away or get worse,it
is a rub or a tick and the woofer should be
replaced. If the noise stays the same,it is normal
suspension noise and the woofer is fine.
Suspension noises will not be heard with
program material.
9. Frequency Response of Bass Channel
NOTE: In order to perform the next three tests,it
is necessary to access the panel assembly which
contains the Main PCB. Refer to Procedure
5,Panel Assembly Removal, in the
Disassembly/Assembly Procedures section.
A. Make up a temporary set of connections to the
woofer output connector J303 (disconnect from
the woofer). The positive wire should be
connected to pin 2 and the negative wire should
be connected to pin 1 . See the figure below for
a reference.
Pin 1
B. Connect an oscillator to the module's L/R
audio input terminals. Adjust the oscillator to 100
Hz,30 mVrms for a 0 dB reference.
Ω
C. Connect a 4
woofer output. Using a dB meter,measure the
response according to the chart below.
Frequency
20 Hz
55 Hz
100 Hz
200 Hz
400 Hz
10. Bass Channel Dynamic EQ Gain
NOTE: Use the same test setup as test
Procedure 9.
A. Adjust the oscillator to 55 Hz,200 mVrms.
The gain relative to the input should be
approximately 35.1 dB.
21
Pin 2
resistive load across the
Relative Response
-10.0 dB ± 1.5 dB
+4.8 dB ± 1.8 dB
0 dB
-1.0 dB ± 1.5 dB
-11.4 dB ± 1.5 dB