JBL LS Series, Service Manual

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LS120P Test Set Up and Procedure
SYSTEM AURAL SWEEP TEST
Equipment needed:
• Function/signal generator/sweep generator
• Integrated Amplifier
• Multimeter
• Speaker cables
General Unit Function (UUT = Unit Under Test)
Switches/knobs on the amplifier faceplate:
LFE/Normal to "Normal"
Low Pass Frequency Adjust full CW (150Hz)
Phase switch – either position
1. From the signal generator, Connect both right and left line level inputs (RCA) to signal generator and UUT.
Use Y-cable if necessary from mono source.
2. On the amplifier, turn the LEVEL control full Counterclockwise (Min).
3. Turn on generator, adjust to
125mV, 50 Hz .
4. Plug in UUT; turn the power switch ON. Turn LEVEL control full Clockwise (Max).
5. LED should now be Green; immediate bass response should be heard and felt from rear port tube opening.
6. Turn off generator, turn LEVEL control fully Counterclockwise (Min), disconnect RCA cable.
Sweep Function
1. Follow steps 1-5 above, using a sweep generator as a signal source.
2. Sweep generator from 20Hz to 1kHz. Listen to the cabinet and drivers for any rattles, clicks, buzzes or
any other noises. If any unusual noises are heard, remove woofer and test.
Driver Function (Woofer)
1. Remove woofer from cabinet; this is accomplished by gently prying the woofer trim ring out of the counterbore,
which is attached with a friction fit, with a small flat-blade screwdriver or similar tool. The eight Phillips screws
will then be visible. Remove woofer and and - wire clips.
2. Check DC resistance of woofer; it should be 3.5 ohms ±10%.
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 5.0 V.
4. Sweep generator from 20Hz to 1kHz. Listen to driver for any rubbing, buzzing, or other unusual noises.
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LS120P