Shure Incorporated 222 Hartrey Avenue Evanston IL 60202-3696 U.S.A. LX Wireless System 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 update 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.
Service Manual 25D1006 (CG) LX2 Hand-Held Transmitter Characteristics General The Shure LX2 Hand-Held Transmitter is part of a wireless system designed for public address, educational radio and television broadcasting, school and community theater productions, and similar applications. The LX2 is intended for use with the matching LX3 and LX4 receivers.
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 Audio signals from the microphone head enter the transmitter via a printed circuit board (pcb) with spring contacts, which also interconnects the audio and rf printed circuits.
Shure LX2 Hand-Held Transmitter The base-emitter circuit of Q201 operates as a crystal-controlled Colpitts oscillator in the 20 MHz region. Fundamental-mode crystal Y201 is tuned 10 kHz below series resonance by the series combination of frequency-netting coil L201, diode D201, capacitor C203, and capacitor divider C206 and C207. Frequency Stability To ensure frequency stability with changes in battery voltage, regulated 5 Vdc bias is applied to the varactor diode and to the base of Q201.
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). The latter’s base-emitter circuit operates as a crystal-controlled Colpitts oscillator in the 20 MHz region.
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. The unit should be powered exclusively by a 9 Vdc dry battery. An alkaline type such as the Duracell MN1604 is recommended.
Shure LX2 Hand-Held Transmitter Notes: Notes: 6 25D1006 (CG)
Shure LX2 Hand-Held Transmitter Preliminary Tests Listening Test Before completely disassembling the transmitter, operate it to determine 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. Review any customer complaint or request, and focus the listening test on any reported problem. The following, more extensive, functional tests require partial disassembly.
Shure LX2 Hand-Held Transmitter Test Component Locations Audio Board (top) Power (GREEN) D103 Low battery (RED) D101 Ç Ç Ç Ç Ç J102 R125 – U101 R130 U102 + J101 Mic ON/OFF S102 Power ON/OFF S101 Head Board (front view) +9 V (to cartridge) Audio OUT (to rf board) +9 V ÇÇ ÇÇÇ ÇÇ ÇÇÇ ÇÇ ÇÇ +5 V Audio IN (from audio board) Gnd Gnd +9 V Gnd Gold-plated contacts Ç Ç Ç Ç Ç +9 V Audio IN (to audio board) Audio IN (from cartridge) Rf Board (top) (FCC/IC) Ç Ç Ç Ç Ç J101 L209 I210 Y201 R217
Shure LX2 Hand-Held Transmitter Rf Tests ÁÁÁ Á ÁÁÁ Á ÁÁÁ ÁÁÁ Á ÁÁ Á ÁÁ ÁÁÁ ÁÁ Á Á ÁÁ ÁÁ ÁÁ Á Á ÁÁ ÁÁ ÁÁÁ ÁÁ Á ÁÁ ÁÁ Á ÁÁ ÁÁ Á Á ÁÁ ÁÁ Á ÁÁ ÁÁ Á ÁÁ Á ÁÁÁ ÁÁ Á Á ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ Á ÁÁ Á ÁÁÁÁ ÁÁ ÁÁÁ SPECTRUM ANALYZER LX2 Transmitter ÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁÁ Á Á ÁÁ ÁÁ ÁÁÁÁ ÁÁ ÁÁ Á Á ÁÁ ÁÁ Á Á Á ÁÁ ÁÁ Á ÁÁ Á ÁÁ ÁÁ BAT MUTE Spectrum Analyzer Power switch: PWR Center frequency: transmitter frequency Mute switch: MUTE Span: 30 MHz Reference level: + 20 dBm Scale: 10 dB/div Figure 3.
Shure LX2 Hand-Held Transmitter Audio Tests Check the Matching Receiver AUDIO ANALYZER ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Á ÁÁÁÁÁÁÁ Á ÁÁ Á ÁÁ Á ÁÁ Á ÁÁ ÁÁ Á Á ÁÁ ÁÁ Á Á Á Á ÁÁ Á Á Á Á Á Á ÁÁ ÁÁ ÁÁ ÁÁ Á Á Á ÁÁ Á Á ÁÁ Á ÁÁ Á Á ÁÁ Á ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁ Á ÁÁ ÁÁÁÁ LX4 RECEIVER OUTPUTS HI Z ANT POWER BAL ANT B A MIC LINE 12.5 – 18.9 VDC DC BLOCK RF SIGNAL GENERATOR NOTE: DC VOLTAGES ARE PRESENT AT MOST RF TEST POINTS. USE A DC BLOCK ON THE RF SIGNAL GENERATOR TO PROTECT TEST EQUIPMENT.
Shure LX2 Hand-Held Transmitter Check the Transmitter AUDIO ANALYZER Á ÁÁ ÁÁÁ Á ÁÁÁÁÁ Á ÁÁ Á Á ÁÁ Á Á ÁÁ Á Á ÁÁ ÁÁÁÁÁ Á ÁÁ ÁÁÁ ÁÁ ÁÁ Á Á Á Á Á Á Á ÁÁ Á ÁÁÁ Á ÁÁÁÁÁ Á ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Á Á ÁÁ Á ÁÁÁÁÁÁÁ Á ÁÁ Á Á Á ÁÁ Á ÁÁÁÁÁÁÁ Á ÁÁ Á Á Á ÁÁ Á Á ÁÁ Á ÁÁ Á Á Á Á ÁÁ Á Á ÁÁ Á Á Á Á Á Á Á ÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁ TRANSMITTER SHOWN WITH BATTERY CUP REMOVED, AND AUDIO TEST HEAD ATTACHED.
Shure LX2 Hand-Held Transmitter Tested Units If the system components pass the RF and Audio tests, then the system is functioning correctly and does not require tuning and alignment. Disassembly and Assembly ! CAUTION ! Observe precautions when handling this static-sensitive device. Disassembly To access the printed circuit boards of the unit, open the case: 1. Make sure the PWR/OFF switch is in the OFF position. 2. Unscrew the battery cup to access and remove the battery. 3.
Shure LX2 Hand-Held Transmitter Á Á Á ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ Ball screen Retaining ring A Microphone cartridge Head board A Bezel Nameplate Switches Audio circuit board Gain control Rf circuit board Switch actuators ÁÁÁ ÁÁÁ Circuit board guides Handle Gain control access 9 V alkaline battery ÁÁÁ ÁÁ ÁÁÁ Á ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ Battery cup Figure 7. LX2 Hand-Held Transmitter, exploded view. Reassembly 1. Make sure the PWR/OFF switch is in the OFF position. 2.
Shure LX2 Hand-Held Transmitter Service Procedures Measurement Reference dBu is a measure of voltage, and dBm is a measure of power. For example, the HP8903 should be labeled dBu instead of dBm because it is a voltage measurement. These two terms are often used interchangeably even though they have different meanings. Audio levels in dBu are marked as dBm on the HP8903. dB Conversion Chart 0 dBV = 2.
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 equation to determine the operating frequency: Carrier frequency = 9 x (nominal crystal frequency in MHz) – .09 MHz After the new crystal is installed, operational tests and alignment procedures must be performed to ensure that the transmitter is operating correctly.
Shure LX2 Hand-Held Transmitter Table 3 Wireless Frequency Selections, Euro (ETSI) Group Code Frequency Code Frequency (MHz) A AQ EA AY EB EC ZZ EE J/BB NB NC ND K NE NH NJ NK NL S NM NP NR EG NX NY EK NZ PU PB PC PD EH EJ PN PP PQ PR PS PT PV PX PY PZ 173.800 173.800 174.100 174.100 174.500 174.500 175.000 175.000 175.000 176.200 176.600 177.000 177.600 182.000 183.200 183.600 184.600 184.800 186.350 189.000 190.600 191.900 197.600 198.600 200.300 200.350 201.650 203.000 204.200 204.600 208.300 216.
Shure LX2 Hand-Held Transmitter Alignment AUDIO ANALYZER NOTE: Whenever soldering is performed on the curcuit boards, always power off the unit. Ç Ç Ç Ç L209 J101 Y201 R217 + I210 C217 C216 I2GNC240 – J102 RF BOARD (TOP) LX2 Transmitter Audio Analyzer Power supply: 9 Vdc Filters: Power switch: PWR 400 Hz High-Pass: ON Mic switch: MUTE 30 kHz Low-Pass: ON Gain: Mid Figure 8.
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. 2. With the 9.0 Vdc power supply connected, the green LED should be illuminated. 3. Reduce the power supply to 6.6 Vdc. The yellow battery LED should be illuminated. 4. Reduce the power supply to 6.0 Vdc. The red battery LED should be illuminated. 5.
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.
Shure LX2 Hand-Held Transmitter Final Output Power / Frequency Calibration (Domestic) This procedure correctly aligns the transmitter’s operating (output) frequency.
Shure LX2 Hand-Held Transmitter Spurious Emissions and Current Drain: Domestic SPECTRUM ANALYZER Ç Ç Ç Ç J101 L209 Y201 R217 I210 C217 C216 C240 I2GN + – RF BOARD SIDE 1 J102 LX2 Transmitter Spectrum Analyzer Power supply: 9 Vdc Scale: 10 dB/div Power switch: ON Start frequency: 10 MHz Mute switch: MUTE Stop frequency: 1 GHz Reference level: 20 dBm Figure 12. Spurious Emissions and Current Drain Test Set-Up 1. Set the spectrum analyzer as follows.
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.
Shure LX2 Hand-Held Transmitter Final Output Power / Frequency Calibration (Euro) FREQUENCY COUNTER CH 2 ÇÇ ÇÇ ÇÇ ÇÇ ÇÇ CH 1 SPECTRUM ANALYZER L201 LX2 Transmitter Power source: 9 Vdc + J201 C222 R217 C214 C216 TP6 TP7 C226 – J202 RF BOARD (TOP) ETSI Spectrum Analyzer Center frequency: 1/3 of the transmitter freq Power switch: PWR Mute switch: MUTE TP5 Y201 Span: 30 MHz Reference level: + 20 dBm Scale: 10 dB/div Figure 14.
Shure LX2 Hand-Held Transmitter Spurious Emissions and Current Drain: Euro Ç Ç Ç Ç SPECTRUM ANALYZER J201 + J202 – L201 Y201 C214 R217 C222 C226 C216 RF BOARD (TOP) ETSI TP8 TP6 TP5 TP7 TP9 TP1 TP3 4TP 5 TP2 RF BOARD (BOTTOM) ETSI LX2 Transmitter Power supply: 9 Vdc + J201 – J202 Ç Ç Ç Ç Spectrum Analyzer Scale: 10 dB/div Power switch: PWR Start frequency: 10 MHz Mute switch: MUTE Stop frequency: 1 GHz Reference level: 20 dBm Figure 15.
Shure LX2 Hand-Held Transmitter Audio Alignment: Domestic and Euro AUDIO ANALYZER Ç Ç Ç Ç Ç ÁÁ Á ÁÁÁ Á Á ÁÁÁÁÁ ÁÁ Á Á Á Á Á Á ÁÁ Á Á Á ÁÁ Á ÁÁ Á Á Á ÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁ AUDIO BOARD (TOP) C107 R125 S102 S101 J102 – U101 R130 U102 + J101 TRANSMITTER SHOWN WITH BATTERY CUP REMOVED, AND AUDIO TEST HEAD ATTACHED.
Shure LX2 Hand-Held Transmitter Deviation Reference Voltage (Domestic and Euro) AUDIO ANALYZER ÁÁÁÁÁÁÁÁ Á ÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁ Á Á ÁÁÁÁÁÁ Á ÁÁ Á Á Á Á Á ÁÁ Á ÁÁ Á ÁÁ Á Á ÁÁ Á Á ÁÁ ÁÁ Á Á ÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁ Á ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁÁÁ ÁÁÁ ÁÁÁ Á LX4 RECEIVER OUTPUTS HI Z ANT POWER BAL ANT B A MIC LINE 12.5 – 18.9 VDC RF SIGNAL GENERATOR DC BLOCK NOTE: DC VOLTAGES ARE PRESENT AT MOST RF TEST POINTS. USE A DC BLOCK ON THE RF SIGNAL GENERATOR TO PROTECT TEST EQUIPMENT.
Shure LX2 Hand-Held Transmitter Deviation Adjustment (Domestic and Euro) Á Ç Á Ç ÁÁ Á ÁÁ Á Á ÁÁÁÁÁÁ Á ÁÁÁ Á Á ÁÁ Á Á ÁÁ Á ÁÁ Ç ÁÁ Á Á ÁÁÁÁÁÁ Á ÁÁÁ Á ÁÁ Á ÁÁ Á Á ÁÁ Á ÁÁÁ ÁÁ Ç Á ÁÁÁÁÁÁ TRANSMITTER SHOWN WITH BATTERY CUP REMOVED, AND AUDIO TEST HEAD ATTACHED.
Shure LX2 Hand-Held Transmitter Distortion Adjustment (Domestic and Euro) ÁÁÁ ÁÁÁ Á ÁÁÁÁÁ Á ÁÁ ÁÁÁ Á Á ÁÁ Á Á Á ÁÁ Á ÁÁ ÁÁÁÁÁ Á Á ÁÁ ÁÁÁ Á Á ÁÁ Á Á Á ÁÁ Á ÁÁ ÁÁÁ Á ÁÁÁÁÁ TRANSMITTER SHOWN WITH BATTERY CUP REMOVED, AND AUDIO TEST HEAD ATTACHED.
Shure LX2 Hand-Held Transmitter Audio Frequency Response (Domestic and Euro) AUDIO ANALYZER Ç Ç Ç Ç S102 S101 C107 R125 – U101 U102 R130 LX2 Transmitter + Audio Analyzer Power supply: 9 Vdc Frequency: 100 Hz Power switch (S101): PWR Amplitude: 230 mV Mic switch (S102): ON Filters: 400 Hz High-Pass: OFF 30 kHz Low-Pass: ON Figure 20. Frequency Response Test Set-Up Note: Press the LOG/LIN button on the audio analyzer to measure in dB.
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. n Make sure the circuit board ground is 0.0 Vdc. n If there is a short from 9.0 Vdc to ground, try to isolate different parts of the circuit; narrow it down to the rf or audio section.
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. This bias comes from the 9.0 Vdc line through voltage divider R103/R105, then through R106 to pin 5. n Look for open vias, foil shorts, incorrect parts, and bad connections. n If there is audio at pin 7, but not at pin 14, check again for db bias.
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 isolate the problem to the audio or rf section. Check for –2.2 dBv at I118; if not, refer to the Audio section of the circuit description. n If the level is correct at I118, check R217, C220, C227, R208, R216, D201, L209, and C214. The value of C214 is critical to the deviation sensitivity.
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. Emitter bypass capacitors C226 and C223 can be probed with the FET probe. If the rf level measured on each side of the part is not comparable, a defective capacitor is indicated.
Shure LX2 Hand-Held Transmitter Notes: Notes: 34 25D1006 (CG)
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 surfacemount with 1/10 W rating and 1% tolerance. Capacitors: Unless otherwise noted, non-polarized capacitors are surface-mount NPO dielectric types with a 100 V capacity and a 5% tolerance, and polarized capacitors are tantalum types.
Shure LX2 Hand-Held Transmitter Table 5 Audio Board Components: Side 1 Reference Designation Description Shure Part Number S101, 102 Switch 55A178 D101 LED, red 184A18 D102 LED, amber 184B18 D103 LED, green 184D18 R125 Potentiometer 20 k 46B8049 R130 Potentiometer 20 k 146F02 Q106, 107, 108, 109, 110 Transistor 183A38 Q103, 104 Transistor 183A01 Q105 Transistor 183A07 Q201, 203, 204 Transistor 183A03 U101 Compander 188A01 U102 Opamp 188A49 Table 6 Rf Board Component
Shure LX2 Hand-Held Transmitter Table 8 Rf Board Components: EURO (ETSI) Reference Designation R201 Shure Part Number Description Potentiometer 1% 10 k 146E02 Table 9 Frequency Dependent Tables Rf Board Components: EURO (ETSI) Group Frequency Range C208 C244 C210 C213 C215 A 169.000–174.000 MHz B 174.000–181.000 MHz 15 pF –– 1.0 pF 33 pF 100 pF 12 pF 1.0 pF 1.0 pF 33 pF 100 pF C D 181.000–188.000 MHz 12 pF –– 1.0 pF 27 pF 100 pF 188.000–195.000 MHz 12 pF –– 1.
Shure LX2 Hand-Held Transmitter LX2 Hand-Held Transmitter Head Board DOMESTIC and EURO Side 1 I109 I145 I140 I108 I147 I118 J102 I104 I133 J101 Side 2 LX2 Hand-Held Transmitter Audio Board DOMESTIC (FCC/IC approved) 38
Shure LX2 Hand-Held Transmitter Side 1 I201 I209 I210 I202 I218 Side 2 LX2 Hand-Held Transmitter Rf Board: Domestic (FCC/IC approved) 39
Shure LX2 Hand-Held Transmitter Euro (ETSI) Audio Board, Side 1 I102 Euro (ETSI) Audio Board, Side 2 LX2 Hand-Held Transmitter Euro (ETSI) Printed Circuit Boards 40
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 41
Shure LX2 Hand-Held Transmitter LX2 Hand-Held Transmitter: Rf Schematic Diagram EURO (ETSI approved) Printed in U.S.A.
Shure LX2 Hand-Held Transmitter LX2 Hand Held Transmitter Audio Schematic Diagram DOMESTIC and EURO
Shure LX2 Hand-Held Transmitter LX2 Hand-Held Transmitter: Rf Schematic Diagram DOMESTIC (FCC/IC approved) Printed in U.S.A.
