Shure_U2_Wireless_Mic_Service_Manual 电路图.pdf

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1、Shure Incorporated 222 Hartrey Avenue Evanston IL 60202-3696 U.S.A. UHF Wireless System ?2000 Shure Incorporated Printed in U.S.A. 2510222 (AG) SERVICE MANUAL CHANGE NOTICE U2 HAND-HELD TRANSMITTER Changes and corrections have been made to the Service Manual for the U2 UHF Hand-Held Transmitter. The

2、se changes will make it easier to repair the transmitters. 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. U2 SERVIC

3、E MANUAL REVISION HISTORY ReleasePart NumberDate Code Original25A1022QE Revision 125B1022SA Revision 225C1022TD Revision 325C1022AG CHANGES EFFECTIVE JULY 2, 2001 REMOVE these pages from the U2 Service Manual INSERT these Revised pages into the U2 Service Manual 22 22 RadioFans.CN 收音机爱 好者资料库 ?1999,

4、Shure IncorporatedPrinted in U.S.A. 25B1022 (AG) Service Manual U2 Hand-Held UHF Transmitter General Characteristics The Shure Model U2 Hand-Held UHF Transmitter is a micro- processor controlled microphone-transmitter operating in the 774 to 862 MHz frequency range. This product is intended for use

5、in high- end installed sound, rental, and concert sound applications. Different frequency variations are available in various countries. Controls and Indicators 9 10 ON OFF 5 1 8 5 4 GAIN 2 6 3 7 1.Grille 2.Programmable Display 3.Battery Fuel Gauge 4.Battery Cover 5.ON/OFF Switch 6.Antenna 7.Battery

6、 Compartment 8.MODE Button 9.SET Button 10. Audio Gain Control Figure 1.U2 Transmitter Controls and Indicators 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: Ope

7、ration may require a user license. Frequency or power-output modifications may violate this products approvals. Contact your countrys communications authorities. RadioFans.CN 收音机爱 好者资料库 Shure U2 Hand-Held UHF Transmitter Circuit Description25B1022 (AG)2 Circuit Description Audio Section Audio enters

8、 L248, an inductor used as an rf choke. The signal is ac-coupled through C201 into a 26 dB user-adjustable gain stage around U201B. This gain stage is externally accessible to the user. C249, C250, and C209 protect the preamplifier and bias circuits from rf interference. R212 and R241 set up a half-

9、supply bias, and R238 sets the ac input impedance. The amplified audio signal is then passed through a pre-emphasis network before entering the compression stage. R230, R202, and C203 set up two corners for the pre-emphasis network. The pre-emphasis boosts the high frequencies before transmission. T

10、his network feeds an NE575 compandor, U203, which utilizes an external amplifier U204B. The compandor performs 2:1 logarithmic com- pression of the audio signal. Additionally, the pre-emphasis network plays a role in setting the hinge point (0 dB gain) of the compandor. Transistors Q211 and Q207, al

11、ong with crystal Y202, form the tone key oscillator circuit. This circuit provides a stable, continuous 32.768 kHz sine wave. Transistor Q201 buffers the tone key signal before it is added to the audio signal. The tone key signal is used in the receiver to provide audio output only when the tone key

12、 signal is present in the transmitted signal; there- fore, if the tone key or the transmitter is turned off, the receiver will be muted. The tone key squelch eliminates receiver noise associated with loss of a carrier. Q206 acts as a switch for toggling the tone key ON/ OFF. It is controlled by the

13、microprocessor. R286 allows for the tone key amplitude level to be set. The tone key circuit is powered via U210B. This is a dc amplifier used to multiply the 3V battery voltage up to 4.5 V (gain = 1.5). As the battery voltage drops, the tone key supply voltage drops, decreasing the amplitude of the

14、 oscillator. This is used to detect low battery in the receiver. (This feature was eliminated for JB models.) The tone key signal, along with the processed audio signal, is then fed to a summing amplifier U204A. R231 and R234 set up a half-supply bias. R207, at the output of the summing amplifier, i

15、s used to help pre- vent spurious oscillations from the operational amplifier. After passing ac-coupling capacitor C213, the signal is fed to the rf module. Rf Section Processed audio enters an internal potentiometer R227, which is adjusted for 45 kHz deviation (100% modulation) with a -7.2 dBV 1 kH

16、z tone at the output of the front audio stage (pin 1 of U201). (On JB mod- els, R227 is adjusted for 5 kHz deviation with a 67.2 dBV, 1 kHz tone injected into the mic input.) The audio is then fed to the tuning voltage pin of the voltage controlled oscillator (VCO) and modulates the carrier directly

17、. The use of a phase locked loop (PLL) frequency-synthesized system eliminates the need for multiplier stages, resulting in a much higher degree of spectral purity. The VCO is shielded to prevent interfer- RadioFans.CN 收音机爱 好者资料库 Shure U2 Hand-Held UHF Transmitter Circuit Description25B1022 (AG)3 en

18、ce from external rf fields. Regulated 5 Vdc power from the dc/dc con- verter ensures frequency stability even if the battery voltage drops. The VCO is capable of tuning from 782 to 810 MHz with a 1 to 4 V tuning voltage range. At the output of VCO U206, the rf signal splits into two paths. The outpu

19、t of the VCO is coupled by C207 to the frequency control pin of synthesizer U205. The synthesizers internal circuitry divides the signal as necessary to the desired reference frequency of 125 kHz. The synthesizer contains a quartz-controlled reference oscillator circuit operating from a 4.0 MHz crys

20、tal, Y203, that is adjusted by means of trimmer VC201. The transmitter output frequency is user-selectable in pre-set increments. The size of the increment and the overall frequency range depend on the model (KK, JB, MB, MC, MD, etc.). Frequency selection is made via microprocessor U104, which inter

21、faces with the user through the mode/select switches. The output of the synthesizer is a series of pulses which are integrated by a passive loop filter, R226, C231, R251, C237, R243, and C257, to produce a control voltage signal. The control voltage signal is then connected to the VCO through amplif

22、ier U210A which is used to isolate the PLL filter from the audio modulation signals. The VCO output is also coupled to an rf power resistive pad consist- ing of R255, R256, R257, R258, and an LC-matching network containing C270, L202, and C217. The rf power amplifier, a dual gate MESFET, Q203, is fi

23、xed tuned, and configured as a common source device. Amplifier stability is obtained through resistive loading on input R237. The output of Q203 contains a low-pass matching network, L207, and LC-type low pass filter, LP201, providing a high degree of spectral purity. The output of the low-pass filt

24、er feeds a microwave isolator that reduces the production of reverse third-order intermodulation products. The transmitter is capable of delivering +10 dBm (10 mW), maxi- mum to the 50 helical antenna. During transmitter power up and fre- quency selection, the rf power is muted by bringing the base

25、of Q209 high. This provides approximately 45 dB rf attenuation until the PLL has locked. The transmitter rf is then unmuted by bringing the base of Q209 low. During transmitter power off conditions, voltage is first removed from the VCO by bringing the base of Q208 high. In this way, the transmitter

26、 carrier signal is not allowed to drift off frequency during power on or power off conditions. U2 Display Board The Display Board consists of following circuitry blocks: Microcontroller Section The microcontroller section consists of microcontroller U104 and the liquid crystal display (LCD). The mic

27、rocontroller has an on-board LCD driver. R104, R105, and R107 supply the microcontroller with the LCD drive voltage for a 4-plex drive. The LCD indicates the UHF frequency group and channel, and also has a battery fuel gauge. A 4.000 MHz oscillator, Y101, provides the Shure U2 Hand-Held UHF Transmit

28、ter Circuit Description25B1022 (AG)4 operating frequency to the microcontroller. The oscillator circuit includes C102, C103, R106. R108. U105, R113, and C107 form the reset circuit. U105 is the reset IC that resets U104 microcontroller if the 5 Vdc normal operating voltage falls below 3.5 Vdc. R112

29、is the pull-up resistor for the U104 programming voltage pin. Memory Section The memory section consists of U101, a nonvolatile EEPRAM chip that stores current transmitter settings and has the mapping of the com- patible groups and channels. Battery Management Section The battery management section

30、consists of comparator U103. It is used to measure the effective battery voltage, with reference to +5 Vdc, by measuring the time taken to charge capacitor C105 to a reference threshold of 0.1 VDE 0.01 Vdc. The battery is checked approximately every five seconds. Comparator U103 alternately charges

31、C105 with +5 Vdc reference and then the battery voltage (DPLUS signal). The micro- controller calculates the battery voltage by comparing the time difference to charge C105, up to a reference threshold of 0.1 Vdc 0.01 Vdc, with the +5 Vdc reference voltage and the battery voltage. User Interface Sec

32、tion The user interface section consists of power, MODE, and SET switches. The LCD provides the user with feedback for all switch operations. Shure U2 Hand-Held UHF Transmitter Preliminary Tests25B1022 (AG)5 Preliminary Tests Test Component Locations TOP BOTTOM DIGITAL DISPLAY BOARD TOP BOTTOM RF-AU

33、DIO BOARD R227 location for F and earlier board versions. R227 location for G and later board versions. Figure 2.Test Component Locations Shure U2 Hand-Held UHF Transmitter Preliminary Tests25B1022 (AG)6 Listening Test Before completely disassembling the transmitter, operate it to deter- mine whethe

34、r it is functioning normally and try to duplicate the reported malfunction. Refer to the User Guide for operating instructions, trouble- shooting, and specifications. Review any customer complaint or request, and focus the listening test on any reported problem. The following, more extensive, functi

35、onal tests require partial disassembly. Functional Tests Refer to the Disassembly section to partially disassemble the transmitter for the following functional tests. Use dc blocks at all rf outputs to protect test equipment. Use a U4 receiver for the following functional tests. Test Set-Up 1.Dc vol

36、tages are present at most rf test points. Use dc blocks to protect the test equipment, if necessary. 2.Insert two fresh AA batteries into the U2 battery nest. 3.Connect the audio analyzer to the microphone via the microphone test head. Rf Power 1.Attach a U4 antenna to the spectrum analyzer. 2.Turn

37、the U2 on and hold it very close to the antenna. Move the U2 up and down to maximize power on the spectrum analyzer. 3.Verify that output power is greater than 3 dBm. Current Drain 1.Apply 3.0 Vdc to the battery terminals. 2.Connect the amp meter between the positive (+) battery lead and the positiv

38、e (+) battery terminal of the U2 transmitter. 3.Verify that the current drain is less than 110 mA. Shure U2 Hand-Held UHF Transmitter Preliminary Tests25B1022 (AG)7 Frequency Response Values between board versions may vary slightly; the following values are typical values. 1.With the transmitter set

39、 to minimum gain, apply 100 mVrms at 1 kHz to its input. If you have a version with a 6 dB pad (JB model), apply 200 mVrms at 1 kHz. 2.Connect the audio analyzers input to the unbalanced output of the U4 receiver. 3.Make sure the receiver volume control is set to maximum. 4.With respect to the 1 kHz

40、 level, measure 8.5 dBu 2 dB. 5.Change the frequency to 100 Hz and verify that the measure- ment from the U4 unbalanced output is within 3.0 dB with respect to the 1 kHz level. 6.Change the frequency to 10 kHz and verify that the measure- ment from the U4 unbalanced output is within 1.5 dB with resp

41、ect to the 1 kHz level. Shure U2 Hand-Held UHF Transmitter Notes25B1022 (AG)8 Notes This page intentionally left blank. Shure U2 Hand-Held UHF Transmitter Disassembly and Assembly25B1022 (AG)9 Disassembly and Assembly ATTENTION Observe precautions when handling this static-sensitive device. 1.Refer

42、to Figure 2 and remove the microphone head from the U2. 2.Remove the retaining ring from inside the top of the case, using a pair of needle-nosed pliers. 3.Remove the screw located beneath the battery cup. 4.Slide the circuit board assembly out by pushing up on the antenna. 5.After completing all re

43、pairs, slide the circuit boards back into the case; then reinstall the retaining ring, screw and microphone head. ANTENNA PRINTED CIRCUIT BOARD ASSEMBLY MICROPHONE HEAD RETAINING RING BATTERY NEST CASE BATTERY CUP RF GROUND SCREW CONDUCTIVE WASHER “O” RING Figure 3.U2 Transmitter Disassembly and Ass

44、embly Shure U2 Hand-Held UHF Transmitter Notes25B1022 (AG)10 Notes This page intentionally left blank. Shure U2 Hand-Held UHF Transmitter Service Procedures25B1022 (AG)11 Service Procedures Service Note Units With Date Codes Earlier Than August 1996 A small number of synthesizer ICs (U204) can exper

45、ience start-up problems with the 4 MHz crystal reference oscillator. The problem will only occur for certain values of tuning capacitance. The transmitter displays the correct group and channel information. However, the carrier will have moved to its lowest possible frequency (around 750 MHz). The t

46、uning voltage of the VCO will read 0 Vdc. Adjusting the crystals tuning capacitor to its lowest value should cause the 4 MHz crystal oscillator to start up, and the carrier will lock to the proper frequency. The tuning capacitor can now be readjusted to center the carrier to within 1000 kHz. However

47、, once the unit is turned off, the problem may return. All units with August 1996 date codes or later have a 10 k resistor from pin 2 of the synthesizer to ground to insure that the internal oscillator will start up for all values of tuning capacitance (C239). Safe values for the resistor are from 1

48、6.8 to 33.2 k. Shure U2 Hand-Held UHF Transmitter Service Procedures25B1022 (AG)12 Antenna Replacement The top printed circuit board (pcb) is connected to the bottom pcb by a multipin connector. Two wires also lead to the battery connector and a three-wire flat cable that connects the pcbs to the mi

49、crophone jack. Handle the pcbs with care to avoid damaging these connections. 1.Open the battery compartment cover and remove the batteries. 2.Remove the belt clip. 3.Remove the two screws from the back of the case. 4.Lift the top half of the transmitter case away to expose the pcbs. 5.Remove the single screw visible next to the antenna connector. 6.Use the antenna to gently lift up both pcbs far enough so that the antenna assembly clears the case, or remove the top pcb to gain better access to the bottom pcb. 7.Remove the antenna by unscrewing it from the connector. Make