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JBL LSR28P, Technical & Service Manual

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JBL LSR28P Technical & Service Manual Download Page 9

9

ESSENTIAL TOOLS

In order to successfully service and maintain this speaker system, the technician
should have, at a minimum, the following test instruments.

Oscilloscope, at least 20 MHz bandwidth

Digital Multimeter, with a minimum of 50kohm Impedance for various

troubleshooting

Line Voltage Variac with Ammeter for measuring proper voltage/ current

consumption.

Hand tools (i.e. screwdrivers, pliers’ etc.)

4 ohm resistive load capable of handling 500 watts continuous.

Serial Number specific schematic diagram

Summary of Contents for LSR28P

Page 1: ...1 Technical Service Manual Rev A 3 14 2003...

Page 2: ...TIBLE INPUT SENSITIVITY 15 BLOCK DIAGRAM 16 THEORY AND CIRCUIT DESCRIPTIONS 17 25 POWER SUPPLY INPUT BUFFER AMPLIFIER LOW FREQUENCY PROCESSING HIGH FREQUENCY PROCESSING FINAL LOW FREQUENCY FILTER LOW...

Page 3: ...al signal frequency processing and power amplifier modules The composite signal is efficiently separated into the low and high frequency components by utilizing BI amplified topology for signal dispen...

Page 4: ...00 10 00 5 000 0 0 5 0000 10 000 LEVEL dBu 2 CHAN dBu 20 100 1k 10k 50k FREQ Hz When a system under test shows a different result in the frequency response test as shown above using a 4dBu input sign...

Page 5: ...NT There are no user servicible parts inside Attempting to repair this product or opening the cabinet will expose the user to hazardous high voltage Servicing and repair should be referred to authoriz...

Page 6: ...6 LIABILITY WAIVER JBL PROFESSIONAL IS NOT LIABLE FOR ANY DIRECT OR INDIRECT DAMAGE TO THIS OR ANY ASSOCIATED PROPERTY ARISING FROM THE USAGE OR THE INABILITY TO USE THIS PRODUCT...

Page 7: ...Resonance Frequency 38 Hz Low Frequency Transducer JBL 218F 203mm 8 in Cone DC Resistance 1 8 ohm 10 Differential Drive Dynamic Braking High Frequency Transducer JBL 053Ti DC Resistance 3 5 ohm 3 8 oh...

Page 8: ...ial and workmanship for a full five years from the original date of purchase Electronic components and circuitry is warranted for three years For more specific information consult the warranty card th...

Page 9: ...ents Oscilloscope at least 20 MHz bandwidth Digital Multimeter with a minimum of 50kohm Impedance for various troubleshooting Line Voltage Variac with Ammeter for measuring proper voltage current cons...

Page 10: ...the electronic circuitry not associated with the fault and concentrate on the problem area Testing for typical voltages and oscilloscope waveforms at various test points and as a last resort initiatin...

Page 11: ...he PCB connections at the component legs to an actual failure of the electromechanical components intermittent DIP switches noisy potentiometers faulty connectors The printed circuit boards and their...

Page 12: ...plane and carried onward to the amplification process The second method of hookup called an unbalanced input is by using phone plug which is predominantly used within the semiprofessional environment...

Page 13: ...UNBALANCED CONNECTIONS SUGGESTED INSTRUMENT SETUP INPUT METER OUTPT METER CHNL CHNL 1 2 DISTORTION ANALYZER UNIT UNDER TEST VOLT OHM METER VARIAC WITH CURRENT METER ISOLATION XSFRMR O SCOPE 4 LOAD SIG...

Page 14: ...umer audio industry The tip of the TRS connector or the center conductor of the phonograph cable is the hot lead and should be connected to Pin 2 of the XLR connector for signal transfer The use of th...

Page 15: ...with the use of a pen or a very small screwdriver These are the DIPswitches Switch 1 enables the input trim potentiometer when switched to the up position This potentiometer is located to the left of...

Page 16: ...16 HFP LFP 3 BLOCK DIAGRAM LSR28P Signal Gain Trim DIP Switch PreAmp PreAmp PWR AMP PWR AMP HF LF Speaker Speaker TRIM TRIM...

Page 17: ...17 THEORY AND CIRCUIT DESCRIPTIONS...

Page 18: ...ve 15 volts to drive the housekeeping fault detection circuitry Voltage doubling circuitry supplies the positive and negative 70 volts necessary to supply the drivers and predrivers By utilizing this...

Page 19: ...deterioration caused by the user selectable DIP switches SW1A B AND C The resultant gain of U3B will vary depending upon which DIP switches are enabled The final composite signal on pin 7 U3B is sent...

Page 20: ...2 R1R2C1C2 1 2 where R1 9k R2 10k C1 C2 10nF 1 677kHz Because of this relationship the frequency response will roll off or be attenuated at a rate of 40 dB per decade assuring a gain of 707 volts at...

Page 21: ...al frequency This circuit is located on the input printed circuit board and is instituted after the isolation buffer integrated circuit U3 The signal then enters the operational amplifier U2B where th...

Page 22: ...nd attenuates that signal at a rate of 40 dB after the critical frequency The circuits main purpose is to verify that only low frequencies are passed on to the low frequency amplifier reducing the pos...

Page 23: ...p at C27 and turns Q17 off after a short pause of about 4 seconds The comparator U1B then toggles taking its output high and biasing on the constant current source at Q19 and hence enabling the low fr...

Page 24: ...re B attenuation of feedback network R53 R53 R36 06976 1 06976 14 33 14 3 Signal input from the previous printed circuit board is capacitively coupled by C25 and serially reduced by R52 and connected...

Page 25: ...however the red LED or a combination of the red and green LED s illuminate the circuitry has detected a fault or there is a fault in the detection circuitry itself In either case the muting circuitry...

Page 26: ...very apropos in all societies so it is with electronic repair The technician therefore must be time efficient with respect to diagnosing and repairing equipment Visually inspect product Many times a c...

Page 27: ...on is restored replace the switch Similarly exercise the voltage selector switch SW2 and replace if indicated by the test 2 If the fuse blows the fault is most likely in the main board Refer to the gu...

Page 28: ...ns FET Q1 or I C op amps U1 8 Loss of output or high noise or distortion can usually be easily isolated to a particular integrated circuit For the low frequency path apply a sine wave signal at 440 Hz...

Page 29: ...ponse 30 00 25 00 20 00 15 00 10 00 5 000 0 0 5 0000 10 000 LEVEL dBu 2 CHAN dBu 20 100 1k 10k 50k FREQ Hz Where the system under test shows a different result in a frequency response test using a 4dB...

Page 30: ...fication of a stage which is causing frequency response errors An inaccuracy in a single section can result in gross inaccuracies in the overall response result AUDIO PRECISION LSR28PL1 vs Low Frequen...

Page 31: ...h flat response down to about 30Hz with a well damped roll off below 30Hz is the standard response with all switches down AUDIO PRECISION LSR28PLb vs Bass Adjustments 30 00 25 00 20 00 15 00 10 00 5 0...

Page 32: ...nd order high pass filter U4 A and B along with U8B form twin bell equalization boosts centered at about 4 3KHz and 11KHz The response at any point along the signal path relies on an accurate frequenc...

Page 33: ...own in the curves at the figure below The highest gain curve is the result of selecting SW1H whereas the lowest gain curve is the result of selecting SW1G The middle curve is the standard response wit...

Page 34: ...is in the range of 20V power down the unit and proceed to the Excessive line current test If the current drawn stays within 1 to 2 amps and the 15 volt supply stays within regulation verify other vol...

Page 35: ...r Amplifier Test Note The integrated power amplifier will begin to shutdown due to thermal limitations after only a few seconds Do not be misled that a fault condition exists if the output is not as e...

Page 36: ...traces between main bridge D13 and the main filter capacitors C16 C17 Look of open traces between D13 and power input connector J1 Verify that D13 is not open Return to Main Test Loop after fault fou...

Page 37: ...red LF test point TP4 and output leg is not shorted there could be a problem with the bias reference Jumper across C1 Power unit If excessive current is not pulled bring AC supply to full 120VAC Measu...

Page 38: ...d off right around crossover crossover from positive drive to negative drive This actually takes a small chunk sometimes only visible in distortion waveform out of the center of the output waveform Th...

Page 39: ...aracteristics of the waveform and then probe on both sides of C1 C1 is across the input to the current amp If the waveform visibly appears almost identical to the output waveform same P P voltage same...

Page 40: ...or around 40VP P if the condition of the board allows this much voltage Visually note the characteristics of the waveform and then probe on both sides of C1 C1 is across the input to the current amp I...

Page 41: ...eference The range measure across C1 should be 1 7V to 2 8V If not check R12 R13 R14 R16 and Q3 After amplifier heats up bias current and power pulled from AC line increases This is due to bias circui...

Page 42: ...vices 20 If voltages are not matched or if they are higher or lower verify values of R30 and R28 3K24 R29 464ohm and R11 150 ohm and check for open or shorted elements in Q18 Q16 Q14 or Q12 2 Upper Cl...

Page 43: ...t the base of Q11 will equal 36 10 2 13V Under normal conditions when the output is at zero volts the base of Q11 is at 18 volts If incorrect check values of R20 and R19 63K4 If R20 and R19 are correc...

Page 44: ...erly Sweep the oscillator frequency and note if the readings are reasonably close to the values indicated in the plot above 10 For example with a filter that operates normally the output will be 2 8 P...

Page 45: ...shorts are found replace U2 Verify that pin 9 reflects the output offset polarity i e the voltage across R36 should be insignificant If not look for shorts surrounding pin 9 and verify values of R36...

Page 46: ...ffsets at both power amplifier outputs If substantial negative offset detected refer to Low Frequency Power Amplifier Test and to High Frequency Power Amplifier Test If these are correct replace U3 Ve...

Page 47: ...t C38 is correct polarity Check values of R62 14K ohm R65 10K ohm and R64 100K ohm If all these are okay replace U3 Verify 7 5 volts at U3 pin 10 If not check values of R63 and R60 Both 15 K ohm If th...

Page 48: ...If the signal is erratic this will be displayed on the oscilloscope and indicates a faulty volume control Set the frequency on the signal generator to 100 Hz The LF output level should be approximate...

Page 49: ...49 Click here to view component exploded view http www jblproservice com pdf LSR 20Series LSR28P pdf...

Page 50: ...1 SW Voltage Selector SW2 2 660 00027 01 1 RES TRIM POT 5K R56 8 660 00027 00 1 RES TRM POT 500 R4 3 684 00000 00 3 IC NJM2068D U1 U4 U8 9 548 00018 01 1 SW DIP 8 WAY SW1 4 546 00004 00 1 SW Power SW3...

Page 51: ...RR6 R8 R23 R2 5 2 682 00006 00 3 XSTR NPN 2SD1763A Q1 Q2 Q3 8 604 06109 60 2 CAP 10 000 UF 63V C16 C17 3 548 00015 00 1 SW THERM 67F090 SW1 9 684 00003 00 1 IC NJM4560D U1 4 682 00007 00 2 XSTR PNP 2S...

Page 52: ...52 Wiring Diagram LSR28P...

Page 53: ...53 SEMICONDUCTOR PINOUTS...

Page 54: ...SSEMBLY COMPONENT PARTS LIST Item Part No Qty Description 1 124 58002 00x 1 Speaker low freq 218F 2 123 10003 00X 1 Speaker H F M I 053TI 3 226 00013 00 1 Main Amp Assy W Heatsink 4 226 00012 00 1 Sig...

Page 55: ...55 LSR28P PICTORIAL OF INTERFACE PCB ASSEMBLY COMPONENT PARTS LIST Item Part No Qty Description 1 513 00034 01 2 Interface Cable Assembly...

Page 56: ...0 1 SW Voltage Selector SW2 2 660 00027 01 1 RES TRIM POT 5K R56 8 660 00027 00 1 RES TRM POT 500 R4 3 684 00000 00 3 IC NJM2068D U1 U4 U8 9 548 00018 01 1 SW DIP 8 WAY SW1 4 546 00004 00 1 SW Power S...

Page 57: ...R6 R8 R23 R25 2 682 00006 00 3 XSTR NPN 2SD1763A Q1 Q2 Q3 8 604 06109 60 2 CAP 10 000 UF 63V C16 C17 3 548 00015 00 1 SW THERM 67F090 SW1 9 684 00003 00 1 IC NJM4560D U1 4 682 00007 00 2 XSTR PNP 2SB...

Page 58: ...R 20Series LSR28P 20AMP 20BOM pdf Click here to view the JBL Professional Electronic Failure QA Codes http www jblproservice com protected Domestic 20pdf Electronic 20QA 20Codes pdf Click here for Sch...

Page 59: ...the next section of this warranty How to Obtaln Warranty Pertormance If your JBL product ever needs service write or telephone us at JBL Incorporated Attn Customer Service Department 8500 Balboa Boul...

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Page 67: ...re codes Please utilize these codes on every warranty claim submitted to JBL Professional Exclusion of these codes will result in the return of warranty claims We have designed these codes to be as si...

Page 68: ...ify 10 084 Meter Defective IN 10 031 FET Open IN 10 085 Bezel Broken IN 10 032 FET Burned OUT 10 033 FET Shorted IN 10 090 RELAY Specify IN 10 034 FET Thermally Sensitive IN 10 091 Relay Intermittent...

Page 69: ...Damaged Front Panel OUT 10 151 Regulators Open IN 10 407 Broken Fan OUT 10 152 Regulators Burned OUT 10 408 Stopped Slow Fan IN 10 153 Regulators Shorted IN 10 409 Packing IN 10 154 Regulators Thermal...

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