shure_lx_4 电路图.pdf
Shure Brothers Incorporated 222 Hartrey Avenue Evanston IL 60202-3696 U.S.A. LX Wireless System ?1999, Shure Incorporated Printed in U.S.A. 2510081 (DL) SERVICE MANUAL CHANGE NOTICE LX4 DIVERSITY RECEIVER Changes and corrections have been made to the Service Manual for the LX4 Diversity Receiver. To update your Service Manual, remove the pages identified in the tables below and replace them with the pages at- tached to this Change Notice. Note that there are no changes to pages not specifically identified in the tables below. LX4 DIVERSITY RECEIVER SERVICE MANUAL REVISION HISTORY ReleasePart NumberDate CodeColor Original25A1008QHWhite Revision 125B1008QLPink Revision 225C1008SCTan Revision 325D1008SIWhite Revision 425D1008TLWhite Revision 525D1008BKWhite Revision 525D1008DLRed CHANGES EFFECTIVE DECEMBER 21, 2004 REMOVE these pages from the LX4 Service Manual INSERT these pages into the LX4 Service Manual Pages 26 28Pages 26 28 RadioFans.CN 收音机爱 好者资料库 Characteristics125D1008 (DL) Service Manual 25D1008 (DL) LX4 Diversity Receiver Characteristics General The Shure Model LX4 is a single-conversion superheterodyne diversity FM receiver operating in the 169 to 240 MHz band. It is intended for use with compatible Shure VHF wireless transmitters. Controls and Connectors Figure 1.Identification of Controls and Connectors 1.Diversity signal indicators 2.Rf level indicators 3.Audio level indicators 4.Squelch control 5.Audio level output control 6.Power ON indicator 7.Power ON/OFF button 8.Antenna connectors 9.Output connectors 10. MIC/LINE slide switch 11. Power jack 12.5 18.9 VDC 10 POWER MARCAD DIVERSITY 1 RF ARF BAUDIO SQUELCHLEVEL 24 5 36 7 ANTANT OUTPUTS HI Z BAL MICLINE POWER AB 8 9 9118 Service Note: Shure recommends that all service procedures be performed by a Factory- Authorized Service Center or that the product be returned directly to Shure Brothers Inc. Licensing: Operation may require a user license. Frequency or power-output modifications may violate this products approvals. Contact your countrys communications authorities. ?1999, Shure, Inc. Printed in U.S.A. RadioFans.CN 收音机爱 好者资料库 Shure LX4 Diversity Receiver 2Characteristics 25D1008 (DL) Circuit Description The Shure Model LX4 Diversity Receiver is a single-conversion superheterodyne diversity FM receiver operating in the 169 240 MHz band. It is intended for use with compatible Shure VHF wireless transmitters, including the Shure LX, L, EC, SC, and T series hand-held and body-pack transmitters. The LX4 has balanced LO-Z output (3-pin XLR-type connector), an unbal- anced aux level audio output (1/4 inch monophonic phone jack), and audio output level (volume) control for all outputs. The LX4 has an externally-accessible squelch control for signal-to-noise mut- ing system. The recessed potentiometer for squelch control is screwdriver-ad- justable. A one quarter wavelength whip type antenna can be mounted directly to the receiver or to a full rack panel (Shure model WA440), and can then be cabled to the receiver. Also, a Shure model WA404 antenna splitter can be used to provide antenna inputs and dc power to the LX4. Audio output is a 1/4-inch, single circuit (monophonic) phone jack. Diversity channel selection and muting are provided by a noise- operated squelch system. Noise signals are obtained from the additional detec- tor outputs at pin 9 of U100 and U200. For diversity channel A, the noise signal is adjusted by squelch level control R130 before amplification by U1B. Active high-pass filter U1C removes audio components that could cause false triggering. The noise is then rectified by D2 and smoothed by C18 to pro- vide a dc voltage that varies in accordance with the amount of noise present on the detected signal. An identical scheme is followed for diversity channel B, where noise signals are adjusted by squelch level control R230 before being amplified by U2B, fil- tered by U2C, rectified by D1, and smoothed by C17. Two diversity peak A/B (yellow) LEDS are located on the front of the unit illu- minate to indicate which diversity channel (A, B, or both) have been selected by the receiver. When the quality of the received signal is below the squelch threshold level, both LEDs are extinguished. Audio peak LEDs illuminate when the deviation level of the received signal exceeds the following deviation: LED ColorDeviation kHz 1 Green 1.5 2 Green 4.0 3 Green 7.0 4 Amber11.0 5 Red 14.0 RadioFans.CN 收音机爱 好者资料库 Shure LX4 Diversity Receiver Characteristics325D1008 (DL) Diversity Control Signals The dc noise signals are compared by U3A, U3B, U3C, and U3D to produce diversity control signals. These signals directly control analog switches U6A and U6B, and diversity A/B LEDs D9 and D10. These switches control the flow of audio signals from U1A and U2A. Squelch Control Squelch comparators U3A and U3C compare a dc level from the user squelch control, R66, to the dc noise level signals coming from each diversity channel. When the noise level in both channels exceeds a preset level, the au- dio output of the receiver is squelched. Comparator U4A provides additional signal attenuation in the squelched state by shutting off compander U9B. However, if the noise level in each channel is comparable and below the squelch threshold, then U3B and U3D will allow both channels to be active and both diversity indicators will be illuminated. Because the signals from each channel are correlated, but the noise is uncorrelated, a theoretical signal-to-noise improvement of 3 dB is possible with this arrange- ment. Balanced LO-Z Output After passing through analog switches U6A and U6B, audio signals from the two channels are buffered by U5A before entering three-pole, low-pass filter Q1. They then enter compander U9B, which provides 2:1 logarithmic expansion. An additional IC amplifier U5B operates in conjunction with U9B to provide a lower noise floor. The output of this stage is applied to volume level control R32. In order to provide a balanced LO-Z output, U5C and U5D operate as a bridging amplifier. HI-Z audio output connector J3 taps off U5D output. Audio Indicators An audio LED indicator display lets the user know when the transmitter (and audio level) deviation is approaching the limit of 15 kHz. This function is imple- mented by the U11 display chip. Two rf level LED strings are provided to indicate relative rf strength of transmitters received by each antenna. They are powered by display chips U10 and U12, which are controlled by U100 and U200 signal strength pins. Shure LX4 Diversity Receiver 4Characteristics 25D1008 (DL) Independent Rf Sections Two complete, independent rf sections are provided for diversity reception. Signals enter the receiver via detachable, single-element quarter- wave antennas. For diversity channel A, they pass through a filter that is double- tuned by L100 and L101 before entering dual gate MESFET amplifier Q100. The output of this stage is triple tuned by L103, L104, and L105, which filter the sig- nals before they enter gate 1 of MESFET mixer Q101. The local oscillator (LO) signal, which is applied to gate 2 of Q101, is provided by transistor Q104. A third- or fifth- overtone quartz crystal in the 50 to 70 MHz range is used to provide frequency control. The collector circuit of the oscillator is tuned by L113 and L114 to the third harmonic of the crystal (150 to 210 MHz) to provide the correct injection frequency for a 10.7 MHz intermediate frequency (IF). The output of mixer Q101 is tuned to 10.7 MHz by L108 before being applied to ceramic filter FL100. Transistor Q102 provides IF amplification to make up for filter losses. Signals then pass through a second IF filter, FL101, before entering the integrated circuit IF amplifier/detector, U100. The detected audio is taken from pin 8 and is then amplified by operational amplifier U1A. Rf Channel B Diversity channel B is identical in design to channel A. Signals first pass through a double-tuned filter consisting of L200 and L201 before entering amplifi- er Q200. The output of this stage is triple-tuned by L203, L204, and L205 and fed to gate 1 of mixer Q201. LO injection is provided by buffer transistor Q103, which is tuned by L112 and L111 to the third harmonic of the crystal frequency. The buffer stage helps to isolate the diversity channels from one another by pre- venting crosstalk through the common LO section. The output of mixer Q201 is tuned to 10.7 MHz by L208 before being applied to ceramic filter FL200. Signals are then amplified by transistor Q202 before passing through the second ceramic filter, FL201, before they enter the inte- grated circuit IF amplifier/detector U200. The detected audio is again taken from pin 8 and is amplified in this case by U2A. Rf Indicators Rf LEDs indicate approximate rf signal strength for each channel: LEDSignal Strength, dBm (10 dBm) 1 95 2 90 3 80 465 560 Shure LX4 Diversity Receiver Characteristics525D1008 (DL) Power The Shure LX4 Diversity Receiver operates on 12.5 18 Vdc or from an ac power line with 120 Vac, 60 Hz external power converter; or 220 to 240 Vac, 50/60 Hz for export models. The dc power connector: is a male pin coaxial jack with locking connector. A green power LED, D11, indicates when power is being supplied to the re- ceiver by an external power converter. The circuitry will operate normally with an input of 12.5 to 18 Vdc. Reverse polarity protection is provided by D8, and voltage regulation is accomplished by U7. The power in- put, HI-Z and balanced LO-Z output connectors are filtered to prevent local oscil- lator radiation from the cables and to protect the receiver from the effects of external electromagnetic fields. Shure LX4 Diversity Receiver 6Notes: 25D1008 (DL) Notes: Shure LX4 Diversity Receiver Test Component Locations725D1008 (DL) Test Component Locations Shure LX4 Diversity Receiver 8Preliminary Tests 25D1008 (DL) Preliminary Tests Listening Test Before completely disassembling the receiver, operate it to determine whether it is functioning normally and try duplicating the reported malfunction. Refer to the User Guide for operating instructions, troubleshooting suggestions, 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 dis- assembly. Functional Tests Refer to the Disassembly section to partially disassemble the receiver for the fol- lowing functional tests. Use dc blocks at all rf output to protect test equipment. Verify operation and reported malfunction, referring to the product Users Guide for a description of the unit as well as information on its operation, troubleshooting, and technical data. Shure LX4 Diversity Receiver Preliminary Tests925D1008 (DL) Rf Test Receivers that pass this test do not contain any “drop-out” or “range” problems. 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. 12.5 18.9 VDC POWER RF ARF BAUDIO SQUELCH LEVEL ANTANT OUTPUTS HI Z BAL MICLINE POWER AB MARCAD DIVERSITY DC BLOCK LX4 ReceiverRf Signal Generator Power:ONFrequency:Receiver frequency Level (gain):MaxModulation:None Squelch:Mid Figure 2.Rf Alignment Functional Test Set-Up For channel A: 1.Set the receivers squelch control to its middle position and the volume control to its maximum position. 2.Set the rf generator to the receivers frequency. 3.Remove the receivers antenna. Plug the BNC end of the 50 test cable into the signal generator and the other end to the channel A antenna input. 4.Apply power to the LX4. 5.Verify that the unit unsquelches with rf signals greater than 89 dBm. 6.When the unit unsquelches, verify that the “Rf” LED glows. Repeat this test for channel B. Shure LX4 Diversity Receiver 10Preliminary Tests 25D1008 (DL) Audio Tests 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. AUDIO ANALYZER 12.5 18.9 VDC ANTANT OUTPUTS HI Z BAL MICLINE POWER AB DC BLOCK LX4 ReceiverAudio AnalyzerRf Signal Generator Power:ONOutput amplitude:Set to turn OFF high and low EXT lights on rf signal generator Level: 60 dBm Level (gain):MaxFilters:Deviation:15 kHz Squelch:Mid400 Hz High-Pass:ONModulation:EXT 1 kHz 30 kHz Low-Pass:ONFrequency:receiver frequency Figure 3.Audio Test Set-Up, steps 1 5 Note: The amplitude may have to be adjusted so that neither the HI EXT nor the LO EXT LEDs on the rf signal generator are on. This amplitude should be between 1.4 and 1.5 V rms. 1.Set the rf signal generator level to 60 dBm, its deviation to 15 kHz, and its external modulation to 1 kHz. 2.Adjust the audio analyzers output amplitude so that the high and low EXT lights on the rf signal generator are off. 3.Using a 3.3 k load, connect the receivers unbalanced audio output to the audio analyzer. The receivers volume control should still be in its maximum position. 4.Engage the 400 Hz high-pass filter and the 30 kHz low-pass filter on the audio analyzer. 5.Verify the following receiver measurements: ?Audio level is 400 mVrms, ?90 mV. Record the measurement as a reference level for the following steps. ?total harmonic distortion (THD) is <0.75%. Shure LX4 Diversity Receiver Preliminary Tests1125D1008 (DL) 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. AUDIO ANALYZER 12.5 18.9 VDC ANTANT OUTPUTS HI Z BAL MICLINE POWER AB DC BLOCK LX4 ReceiverAudio AnalyzerRf Signal Generator Power:ONOutput amplitude:Set to turn OFF high and low EXT lights on rf signal generator Level: 60 dBm Gain:MaxFilters:Deviation:15 kHz Squelch:Mid400 Hz High-Pass:OFFModulation:EXT 1 kHz 30 kHz Low-Pass:ONFrequency:Receiver frequency Figure 4.Audio Functional Test Set-Up, steps 6 14 6.Use external modulation only on the rf signal generator. Input a 100 Hz signal from the audio analyzer to the external modulation input of the rf signal generator. 7.Disengage the 400 Hz highpass filter on the audio analyzer. 8.Verify that the receivers unbalanced audio output is within +2 dB, 1 dB of the reference level recorded in step 5. 9.Change the audio analyzers frequency to 10 kHz. 10. Verify that the receivers unbalanced audio output is 7.5 dB to 10.5 dB from the reference level recorded in step 5. 11. Place a 150 load across the receivers balanced output. Verify that it is in the MIC position. 12. Connect this output to the audio analyzer and select the float position. Verify that the output is 65 mVrms, ?15 mV. 13. Remove the 150 load. 14. Take the audio analyzer input out of the float position. Repeat this test for channel B. After all testing has been completed, remove the test cable and reinstall the an- tenna. If the receiver passe
