Read JBL MUSIC 20 SUB Service Manual online
3
Powered Subwoofer
BASS20
TEST PROCEDURE
Equipment Needed:
n
Function generator/signal generator/sweep generator
n
Integrated Amplifier
n
Multimeter
n
Cables - Line level (RCA) and Speaker cables
UUT = Unit Under Test
General Function
1.
Connect both left and right line level inputs (RCA) to signal generator and UUT. Use Y-cable if necessary
from mono source.
from mono source.
2.
Turn on generator and adjust to 100mV, 50 Hz.
3.
Plug in UUT; red LEDshould be ON. Turn power switch to the ON or AUTO position and turn LEVEL control
full clockwise.
full clockwise.
4.
Green LEDshould light, immediate bass response should be heard and felt from port tube openings.
5.
Turn off generator, turn unit to OFF, disconnect RCA cables.
6.
Connect two pairs of speaker cables to high level input terminal on UUT. Cables should be connected to an
integrated amplifier fed by the signal generator. Observe polarity of speaker cables.
integrated amplifier fed by the signal generator. Observe polarity of speaker cables.
7.
Turn on generator and adjust so that speaker level output is 2.5V, 50 Hz.
8.
Turn power switch to the ON or AUTO position and turn LEVEL control full clockwise.
9.
Green LEDshould light, immediate bass response should be heard and felt from port tube opening.
Sweep Function
1.
Follow steps 1-4 above, using a sweep generator as a signal source.
2.
Sweep generator from 20Hz to 300Hz. Listen to the cabinet and drivers for any rattles, clicks, buzzes or any
other noises. If any noises are heard, remove driver and test.
other noises. If any noises are heard, remove driver and test.
Driver Function
1.
Remove one or both drivers from cabinet; remove + and - wire clips.
2.
Check DC resistance of driver; it should be 4.2 ohms.
3.
Connect a pair of speaker cables to driver terminals. Cables should be connected to an integrated amplifier fed
by a signal generator. Turn on generator and adjust so that speaker level output is 5.0V.
by a signal generator. Turn on generator and adjust so that speaker level output is 5.0V.
4.
Sweep generator from 20Hz to 1kHz. Listen to driver for any rubbing, buzzing or other unusual noises.
SERVICE NOTE (120v Version only)
Even though the Bass20 seems to have an on/off power switch, in fact the switch does not
switch the main power off to the amp assembly, even in the OFF position. All AC and DC
voltages within the amplifier are still active, so for safety concerns the AC power cord should
be unplugged before any servicing begins.
switch the main power off to the amp assembly, even in the OFF position. All AC and DC
voltages within the amplifier are still active, so for safety concerns the AC power cord should
be unplugged before any servicing begins.
Click on the first or last page to see other MUSIC 20 SUB service manuals if exist.