Shure LX2 Service Manual
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Shure LX2 Service Manual

Shure LX2 Service Manual

Hand-held transmitter
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SERVICE MANUAL CHANGE NOTICE
LX2 WIRELESS HAND-HELD TRANSMITTER
Changes and corrections have been made to the Service Manual for the LX2 Hand-Held Transmitter. To up-
date your Service Manual, remove the pages identified in the tables below and replace them with the pages
attached to this Change Notice. Note that there are no changes to pages not specifically identified in the
tables below.
LX2 HAND-HELD TRANSMITTER SERVICE MANUAL REVISION HISTORY
Release
Original
Revision 1
Revision 2
Revision 3
Revision 4
Revision 5
Revision 6
Revision 7
CHANGES EFFECTIVE
REMOVE
these pages from the
LX2 Service Manual
E1999, Shure Incorporated
25–1006–1 (CG)
Part Number
JULY 10, 2003
35
Shure Incorporated
222 Hartrey Avenue
Evanston IL 60202-3696 U.S.A.
LX Wireless System
25A1006
25B1006
25C1006
25D1006
25D1006
25D1006
25D1006
25D1006
these new Revision pages into the
LX2 Service Manual
Date Code
QH
QL
SC
SI
TF
BB
BK
CG
INSERT
35
Printed in U.S.A.

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Summary of Contents for Shure LX2

  • Page 1 SERVICE MANUAL CHANGE NOTICE LX2 WIRELESS HAND-HELD TRANSMITTER Changes and corrections have been made to the Service Manual for the LX2 Hand-Held Transmitter. To up- date your Service Manual, remove the pages identified in the tables below and replace them with the pages attached to this Change Notice.

  • Page 2: Controls And Connectors

    The Shure LX2 Hand-Held Transmitter is part of a wireless system designed for public address, educational radio and television broadcast- ing, school and community theater productions, and similar applications. The LX2 is intended for use with the matching LX3 and LX4 receivers. Controls and Connectors LX2/BETA 58 MUTE Figure 1.

  • Page 3: Circuit Description

    Shure LX2 Hand-Held Transmitter Circuit Description The Shure LX2 Hand-Held Transmitter contains three circuit boards; an audio section, an rf section, and a microphone head interface board. It is intended for use with the matching LX3 and LX4 receivers. Audio Section...

  • Page 4: Frequency Stability

    L210, and C241). L211 and C242 match the antenna to the filter. Stable Operation To promote stable operation, the LX2 is designed to minimize the production and radiation of spurious emissions and harmonic energy. In addition to the features described previously, the collector of each rf stage is separately decoupled from the 9 Vdc supply using ferrite chokes, resistors, and bypass capacitors of the appropriate value.

  • Page 5: Audio Input

    Shure LX2 Hand-Held Transmitter Rf: Euro (ETSI) Audio Input Processed audio enters R201, an internal potentiometer that is adjusted for 15 kHz deviation (100% modulation) when the audio section provides a –2.2 dBV, 1 kHz tone. Oscillation The audio then goes to varactor diode D201, which is part of the modulated oscillator-tripler stage (Q201).

  • Page 6: Power Section

    Shure LX2 Hand-Held Transmitter Final Output Transmitter: The transmitter can deliver up to +11.5 dBm (14 mW) to the antenna. No user adjustments permit this value to be exceeded. Testpoint TP6 provides a termination point for the 50 Ω output. C243 and L211 act as a series-resonating network for the battery, which acts as the antenna.
  • Page 7 Shure LX2 Hand-Held Transmitter Notes: Notes: 25D1006 (CG)

  • Page 8: Preliminary Tests

    Shure LX2 Hand-Held Transmitter Preliminary Tests Listening Test Before completely disassembling the transmitter, operate it to deter- mine whether it is functioning normally and try to duplicate the reported malfunction. Refer to the product’s User Guide for operating instructions, troubleshooting, and specifications.
  • Page 9 Shure LX2 Hand-Held Transmitter Test Component Locations Audio Board (top) Power Low battery (GREEN) D103 (RED) D101 Ç J102 R125 – Ç Ç U101 R130 U102 Ç J101 Ç Mic ON/OFF Power ON/OFF S102 S101 Head Board (front view) +9 V...
  • Page 10 Scale: 10 dB/div Figure 3. Rf Functional Test Set-Up 1. Install a new 9 Vdc battery and turn on the LX2. 2. Measure the current drain: it should not exceed 35 mA. 3. Maximize the signal received on the spectrum analyzer by attaching a telescoping whip antenna.

  • Page 11: Audio Tests

    Set the rf signal generator’s amplitude to –20 dBm, modulation to 1 kHz, deviation to 15 kHz, and set the frequency to the LX2 unit’s operating frequency. 2. Connect the audio from the unbalanced output to the audio analyzer with a 3.3 kΩ...
  • Page 12 2. Use an audio test head to input audio into the hand-held trans- mitter. 3. Turn the LX2 ON. 4. Inject a 0.775 V, 1 kHz signal from the audio analyzer into the audio test head. Transmitter gain should be set to minimum.

  • Page 13: Disassembly And Assembly

    Shure LX2 Hand-Held Transmitter Tested Units If the system components pass the RF and Audio tests, then the sys- tem is functioning correctly and does not require tuning and alignment. Disassembly and Assembly ! CAUTION ! Observe precautions when handling this static-sensitive device.
  • Page 14 Handle Gain control access Battery cup Figure 7. LX2 Hand-Held Transmitter, exploded view. Reassembly 1. Make sure the PWR/OFF switch is in the OFF position. 2. Replace the transmitter subassembly (audio, rf, and head circuit board) into the handle. Position it using the internal guides.

  • Page 15: Service Procedures

    *Audio levels in dBu are marked as dBm on the HP8903B. Changing the Frequency System Operating Frequencies The LX2 Hand-Held Transmitter printed circuit board (pcb) is marked with a group letter that identifies the range of frequencies it can operate within.
  • Page 16 Shure LX2 Hand-Held Transmitter Change the frequency by changing the crystal on the rf board. For proper operation, the crystal must be obtained from Shure and must operate within the frequency range of the pcb. Use the following equa- tion to determine the operating frequency: Carrier frequency = 9 x (nominal crystal frequency in MHz) –...
  • Page 17 Shure LX2 Hand-Held Transmitter Table 3 Wireless Frequency Selections, Euro (ETSI) Group Frequency Frequency Printed Circuit Code Code (MHz) Board Assembly 173.800 173.800 174.100 174.100 174.500 174.500 175.000 J/BB 175.000 175.000 176.200 176.600 177.000 177.600 182.000 183.200 183.600 184.600 184.800 186.350...
  • Page 18 Shure LX2 Hand-Held Transmitter Alignment AUDIO ANALYZER NOTE: Whenever soldering is performed on the curcuit boards, always power off the unit. Ç J101 L209 Y201 I210 Ç R217 C240 – C217 C216 Ç Ç I2GN J102 RF BOARD (TOP) LX2 Transmitter...
  • Page 19 Shure LX2 Hand-Held Transmitter Power and Display Check LX2 Transmitter Power supply: 9 Vdc Power switch: PWR Mic switch: MUTE Gain: Mid Figure 9. Power and Display Check Test Set-Up 1. Make sure the power OFF/PWR switch is in the PWR position.
  • Page 20 Shure LX2 Hand-Held Transmitter Rf Alignment: Domestic (FCC/IC) During rf alignment, the transmitter output is terminated in a 50 Ω, nonreactive load RG174 cable and monitored with a spectrum analyzer. No modulation is applied during rf alignment. SPECTRUM ANALYZER Ç...
  • Page 21 Shure LX2 Hand-Held Transmitter Final Output Power / Frequency Calibration (Domestic) This procedure correctly aligns the transmitter’s operating (output) frequency. FREQUENCY COUNTER Ç J101 L209 Y201 Ç I210 CH 2 Ç R217 C240 C217 – C216 CH 1 Ç Ç...
  • Page 22 Shure LX2 Hand-Held Transmitter Spurious Emissions and Current Drain: Domestic SPECTRUM ANALYZER Ç J101 L209 Y201 I210 Ç RF BOARD Ç R217 C240 SIDE 1 C217 C216 – Ç I2GN J102 LX2 Transmitter Spectrum Analyzer Power supply: 9 Vdc Scale: 10 dB/div...
  • Page 23 Shure LX2 Hand-Held Transmitter Rf Alignment: Euro (ETSI) Do not apply modulation during the following rf alignment procedures. If you cannot achieve any of the settings described in this procedure, consult the Bench Checks section. SPECTRUM ANALYZER Ç Ç Ç Ç...
  • Page 24 Shure LX2 Hand-Held Transmitter Final Output Power / Frequency Calibration (Euro) FREQUENCY COUNTER CH 2 CH 1 Ç Ç SPECTRUM ANALYZER Ç Ç Ç Ç L201 Y201 J201 C222 C214 – R217 J202 C216 Ç Ç C226 Ç Ç RF BOARD (TOP)
  • Page 25 Shure LX2 Hand-Held Transmitter Spurious Emissions and Current Drain: Euro Ç L201 Ç Ç Y201 C214 J201 C222 SPECTRUM ANALYZER C226 – R217 C216 J202 Ç RF BOARD (TOP) ETSI Ç Ç J201 – Ç J202 Ç RF BOARD (BOTTOM)
  • Page 26 Figure 16. Audio Alignment Test Set-Up 1. Put the mic (mute) switch in the ON position. 2. Turn the LX2 power OFF. 3. Replace C240 for domestic, C242 for Euro, on the rf pcb. 4. Use a soldering iron to remove the 50 Ω test cable.
  • Page 27 Use a receiver that is the same frequency as the LX2, such as the LX3 or LX4 that came with the LX2. 4. Set the volume control on the front panel of the receiver to the maximum position (full clockwise rotation) and apply power to the receiver.
  • Page 28 1. Make sure the rf output on the rf signal generator is turned OFF. 2. Connect the output of the audio analyzer to the test head. 3. Turn the LX2 power ON. 4. Set the frequency of the audio analyzer to 1 kHz. Make sure that the level at the anode (+) of C107 is still 0.775 V ±...
  • Page 29 Shure LX2 Hand-Held Transmitter Distortion Adjustment (Domestic and Euro) Ç Ç C107 R125 – S102 S101 U101 Ç U102 R130 Ç TRANSMITTER SHOWN WITH AUDIO ANALYZER BATTERY CUP REMOVED, AND AUDIO TEST HEAD ATTACHED. LX4 RECEIVER OUTPUTS HI Z POWER LINE 12.5 –...
  • Page 30 5. Change the frequency of the audio analyzer to 10 kHz. Verify that the audio level is equal to +3.0 ± 0.5 dB relative to the level measured at the anode (+) of C107 at 1 KHz. 6. Turn the LX2 power OFF. 25D1006 (CG) Service Procedures...
  • Page 31 Shure LX2 Hand-Held Transmitter Bench Checks Power Input Problem Dc Input n Verify that 9.0 Vdc ± 0.35 Vdc is present at the 9.0 Vdc test point (U101, pin 13). If this voltage is low, check N33. n Check the power switch bias on Q105 and L101.
  • Page 32 Shure LX2 Hand-Held Transmitter Audio Loss n Make sure mic switch is ON. n Determine where the signal is being lost. Verify audio at U102, pin 7. Then check dc bias at U102, pins 5, 6, and 7. They should be about half of the supply voltage, or around 4.5 Vdc.
  • Page 33 Shure LX2 Hand-Held Transmitter RF Problems: Deviation Domestic (FCC/IC) n There must be a good carrier to get any deviation. n If R217 cannot be adjusted to obtain 15 kHz deviation, try to iso- late the problem to the audio or rf section. Check for –2.2 dBv at I118;...
  • Page 34 Shure LX2 Hand-Held Transmitter n If the power is slightly low and the spurious level is high, check for wrong or open coils at L202, L210, and L206. Note: In addition to the frequency determining components discussed above, bypass capacitors can affect the tuning and power gain of rf stages.
  • Page 35 Shure LX2 Hand-Held Transmitter Notes: Notes: 25D1006 (CG)

  • Page 36: Parts Designations

    Shure LX2 Hand-Held Transmitter Replacement Parts and Drawings Parts Designations The following comments apply to the parts list and the schematic: Resistors: Unless otherwise noted, all resistors are surface- mount with rating and 1% tolerance. Capacitors: Unless otherwise noted, non-polarized capacitors...
  • Page 37 Shure LX2 Hand-Held Transmitter Table 5 Audio Board Components: Side 1 Shure Part Reference Designation Description Number S101, 102 Switch 55A178 D101 LED, red 184A18 D102 LED, amber 184B18 D103 LED, green 184D18 R125 Potentiometer 20 k 46B8049 R130 Potentiometer...
  • Page 38 Shure LX2 Hand-Held Transmitter Table 8 Rf Board Components: EURO (ETSI) Shure Part Reference Designation Description Number R201 Potentiometer 10 k 146E02 Table 9 Frequency Dependent Tables Rf Board Components: EURO (ETSI) Group Frequency Range C208 C244 C210 C213 C215 169.000–174.000 MHz...
  • Page 39 Shure LX2 Hand-Held Transmitter LX2 Hand-Held Transmitter Head Board DOMESTIC and EURO Side 1 I109 I145 I108 I147 I118 I140 J102 I104 I133 J101 Side 2 LX2 Hand-Held Transmitter Audio Board DOMESTIC (FCC/IC approved)
  • Page 40 Shure LX2 Hand-Held Transmitter Side 1 I201 I209 I210 I202 I218 Side 2 LX2 Hand-Held Transmitter Rf Board: Domestic (FCC/IC approved)
  • Page 41 Shure LX2 Hand-Held Transmitter Euro (ETSI) Audio Board, Side 1 Euro (ETSI) Audio Board, Side 2 LX2 Hand-Held Transmitter Euro (ETSI) Printed Circuit Boards...
  • Page 42 Shure LX2 Hand-Held Transmitter Euro (ETSI) RF Board, Side 1 Euro (ETSI) RF Board, Side 2 LX2 Hand-Held Transmitter Euro (ETSI) Printed Circuit Boards...
  • Page 43 Shure LX2 Hand-Held Transmitter LX2 Hand-Held Transmitter: Rf Schematic Diagram EURO (ETSI approved) Printed in U.S.A.
  • Page 44 Shure LX2 Hand-Held Transmitter LX2 Hand Held Transmitter Audio Schematic Diagram DOMESTIC and EURO...
  • Page 45 Shure LX2 Hand-Held Transmitter LX2 Hand-Held Transmitter: Rf Schematic Diagram Printed in U.S.A. DOMESTIC (FCC/IC approved)

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