Bose FREESPACE BMA-125, Service Manual

Page: 13 / 49

13
BMA-125 120V Test Procedures
General Test Setup
Connect a 4
Ω
, 5
Ω
, 8
Ω
and 40
Ω
200W load
to the 4, 5, 8, and 40
Ω
outputs respectively.
Disconnect J1 (located at the equalizer
PCB) and add a jumper from pin 1 (yellow)
to pin 3 (violet) of the J1 connector. This
will bypass the internal equalizer.
Set the tone controls to the center (flat)
position unless otherwise noted.
1. Controls
1.1 Adjust Input Five to the full clockwise
position. Adjust the tone controls to their
center (flat) position and all other volume
controls to their full counter clockwise
position.
1.2 Apply a 100mVrms, 1KHz signal to
Input Five.
1.3 Using the Master volume control,
adjust the output across the 4
Ω
load to
1Vrms. Reference a dB meter to the
output.
1.4 Apply a 100mVrms, 85 Hz signal to
Input Five. Rotate the bass control to the
full counter clockwise position. Measure the
output. It should be -3 dB
±
1dB.
1.5 Rotate the bass control to the full
clockwise position. Measure the output. It
should be 3 dB
±
1dB.
1.6 Apply a 100mVrms, 10KHz signal to
Input Five. Rotate the treble control to the
full counter clockwise position. Measure the
output. It should be -3.5 dB
±
1 dB.
1.7 Rotate the treble control to the full
clockwise position. Measure the output. It
should be 3.2 dB
±
1 dB.
2. 4
Ω
Output
Note: Remove the “4
Ω
” to “PRI” jumper.
Connect a 4
Ω
load between “COM” and
“4
Ω
”.
2.1 Apply a 105Vrms, 1KHz signal to Input
Five. Adjust Input Five to full output at the
4
Ω
output (just before clipping).
2.2 Measure the voltage at the output. It
should be
≥
24Vrms.
2.3 Measure the distortion. It should be
< 0.5%.
2.4 With the 4
Ω
output adjusted to
24Vrms, reference a dB meter to the
output.
Measure the response according to the
following table.
Frequency Output
(dB)
Tolerence
(dB)
20 Hz 0 -2
1 KHz ref -
20 KHz 0 -1.5
3. 8
Ω
Output
Note: Place a jumper between the output
connector labeled “4
Ω
” and the output
connector labeled “PRI”. Connect an 8
Ω
load to the 8
Ω
output and the terminal
marked lo.
3.1 Apply a 120 mVrms, 1KHz signal to
Input Five. Adjust Input Five to full output at
the 8
Ω
output (just before clipping).
3.2 Measure the voltage at the 8
Ω
output.
It should be
≥
32Vrms.
3.3 Measure the distortion. It should be
< 0.5%.
3.4 With the 8
Ω
output adjusted to
31 Vrms, reference a dB meter to the
output. Measure the response according to
the following table.