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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 

            

 

 

 

 

 

 

 

  

 
 

Summary of Contents for LS Series

Page 1: ...LS Series LS120P Amplifier Subwoofer SERVICE MANUAL JBL Consumer Products 250 Crossways Park Dr Woodbury New York 11797 Rev0 4 2008 Released 2008 Discontinued XXXX...

Page 2: ...50Hz to 150Hz 24dB octave continuously variable Frequency Response 25Hz 150Hz or Low pass crossover setting Dimensions H x W x D 20 1 16 x 14 3 4 x 17 1 4 510mm x 375mm x 438mm with feet controls gril...

Page 3: ...driven Normal System Gain in dB 39 17 dB Reference Single input driven Normal Signal to Noise SNR A Weighted 100 dBA 95 relative to rated A Weighting filter SNR unweighted 90 dBr 85 relative to rated...

Page 4: ...om line voltage Maximum allowable input power under nominal Input voltage and frequency HOT or COLD operation LED GREEN Power Cons rated power 384 Watts 416 nom line voltage 150 Watts 4 Ohms nominal P...

Page 5: ...4 LS120P...

Page 6: ...ONNECTIONS LS120P 0 Phase Switch 1 LFE Normal Selector 2 Subwoofer Level Control 3 Crossover Adjustment 4 Power Indicator 5 Line Level LFE Input 6 Power Switch 0 1 2 5 6 3 4 JBLP2555LS120P 120Vom 4 16...

Page 7: ...t 5 If your receiver processor does not contain a Dolby Digital or DTS processor but has subwoofer outputs Set LFE Normal switch to Normal NOTE If your receiver processor has only one sub out you may...

Page 8: ...re system so the bass can be felt as well as heard However overall balance must be maintained or the music will not sound natural An experienced listener will set the volume of the subwoofer so its im...

Page 9: ...52 FM04020D605 E Screw amplifier 18 5 30PR14FZD DW01 E 12 Woofer 1 6 Not for Sale LS120P Cabinet 1 7 Not for Sale Damping 1 8 249HIPS 05093 0BAE Port Tube 1 9 Not for Sale LS120P Amplifier 1 10 357 XM...

Page 10: ...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 cabi...

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Page 13: ...k fuse transformer D123 D124 etc Check Class300W MODUL Check D130 R263 265etc Check vbbp vbbp DC voltage Check Relay K101 etc Check Q116 Q117 Q118 D122 Check Q102 101 U103 etc Check P104 pin8 signal C...

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Page 19: ...TAL FILM RESISTOR 2 37K 1 6W 1 RoHS 1 R253 116 162372F26 E METAL FILM RESISTOR 23 7K 1 6W 1 MF RoHS 1 R189 116 162803f26 e METAL FILM RESISTOR 280K 1 6W 1 MF RoHS 1 R201 116 163011F26 E METAL FILM RES...

Page 20: ...W 5 CF RoHS 1 R240 110 16333j26 e CARBON RESISTOR 33K 1 6W 5 CF RoHS 1 R211 110 16391j26 e CARBON RESISTOR 390 1 6W CF RoHS 2 R243 R246 110 16472J26 E CARBON RESISTOR 4 7K 1 6W 5 CF RoHS 4 R213 R217 R...

Page 21: ...118 12061002J E SMD RESISTOR 10 0K 1206 5 RoHS 5 R29 R30 R30B R7 R9 118 120610R0J E SMD RESISTOR 10 0 1206 5 RoHS 4 R20 R20B R22 R23 118 12062002F E SMD RESISTOR 20K 1206 1 RoHS 1 R26 118 12062201J E...

Page 22: ...700mm 18 UL1015 205 0 5t BLACK 250 0 8t R 1 180 PRF1003B E POWER SWITCH ROCKER RF 1003 BB210 RoHS 1 193 0s4211 e INSULATOR INSULATION SPACER 42 11 RoHS 1 193 201612tr e INSULATOR T0 220 16mm 12mm RoH...

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