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Т4
User Manual
31 pgs883.2 Kb0

Shure Т4 User Manual

Shure Incorporated 222 Hartrey Avenue Evanston IL 60202-3696 U.S.A.
T Wireless System
SERVICE MANUAL CHANGE NOTICE
T4 DIVERSITY RECEIVER
T4 RECEIVER SERVICE MANUAL REVISION HISTORY
Release Part Number Date Code Color
Original 25A1020 QG White Revision 1 25B1020 SB Pink Revision 2 25C1020 SI White Revision 3 25C1020 TF White Revision 4 25C1020 CC White
Revision 5 25C1020 EA Red
CHANGES EFFECTIVE JANUARY 13, 2005
REMOVE
these pages from the
T4 Service Manual
21 & 22 21 & 22
INSERT
these new Revision pages into the
T4 Service Manual
E1999, Shure Incorporated Printed in U.S.A. 25–1020–1 (EA)
Characteristics
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General
This manual tells how to service and align the Shure T4 Diversity Receiver (Figure 1). This single-channel, crystal-controlled unit operates within the 169 MHz to 238 MHz VHF-FM band.
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®
Service Manual
25C1020 (EA)
T4 Diversity Receiver
1
2
T4G
T4V
9
DC INPUT
12-18 VDC
1
DC INPUT
12-18 VDC
2
SQUELCH
MIN
SQUELCH
MIN
3
MAX
MAX
E1999, Shure, Inc. Printed in U.S.A.
25C1020 (EA)
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Figure 1. Controls and Connectors
1. “DC Input” jack
2. Squelch control
3. Antennas
4. “Power” LED
5. “Diversity” LEDs
6. “Audio Peak” LED
7. Volume control
8. Audio “Output” (1/4Ȃ phone jack)
9. “Balanced Low Z” audio out­put (XLR)
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.
1 Characteristics
Shure T4 Diversity Receiver
Circuit Description
The Shure Model T4 is a single-conversion superheterodyne diversity FM receiver operating in the 169–238 MHz band. It is intended for use with the matching Shure T Series wireless transmitters.
RF Stages
Two complete, independent RF sections provide diversity reception. Signals enter via the single-element, quarter-wave antennas.
Channel A: The signals pass through a double-tuned filter (L3 and L4) be­fore entering MOSFET amplifier Q1. The output of this stage is double-tuned by L5 and L6, which also provide impedance-matching to Gate 2 of GaAs MESFET (gallium arsenide metal semiconductor field effect transistor) mixer Q3. Gate 1 receives the local oscillator signal from transistor Q5. A third-overtone quartz crystal in the 50–70 MHz range provides frequency control. The collector circuit of the oscillator is tuned by L8 to the third harmonic of the crystal (160–230 MHz) to provide the proper injection frequency for a 10.7 MHz intermediate frequency (IF).
Channel B: This channel is identical in design to channel A. The signals from the antenna pass through a double-tuned filter (L12 and L13) before enter­ing MOSFET amplifier Q6. The output of this stage is double-tuned by L14 and L15 and fed to Gate 2 of GaAs MESFET mixer Q8. Gate 1 receives the local os­cillator injection from buffer transistor Q4, which is tuned by L7. The buffer stage helps isolate the diversity channels from one another by preventing crosstalk through the common local oscillator section.
IF and Audio-Detection Stages
Channel A: L2 tunes the output of mixer Q3 to 10.7 MHz before the signal enters ceramic filter FL3. Transistor Q2 provides IF amplification to make up for the losses in the filters. After passing through a second IF filter, FL2, the signal enters amplifier/detector U1. The detected audio from pin 6 is amplified by U105C.
Channel B: L11 tunes the output of mixer Q8 to 10.7 MHz before the signal enters ceramic filter FL6. Transistor Q7 provides IF amplification before the signal passes through the second ceramic filter, FL5, and enters amplifier/detector U2. The detected audio from pin 6 is amplified by U108B.
Noise-Operated Squelch
A noise-operated squelch system provides both diversity-channel selection and muting. Noise signals are obtained from the additional detector outputs at pin 7 of U1 and U2.
Noise Signals
Channel A: The squelch level control (R16) adjusts the noise signal from U1
before it is amplified by U105A. Active high-pass filter UI05D removes audio components that could cause false triggering. The noise is then rectified by D101 and smoothed by C111 to provide a dc voltage that varies with the amount of noise present on the detected signal.
2Characteristics
25C1020 (EA)
Shure T4 Diversity Receiver
Channel B: This follows an identical scheme: noise signals from U2 are ad­justed by squelch level control R41 before being amplified by U108C, filtered by U108A, rectified by D107, and smoothed by C140.
Comparator Circuits
U106C and U106D compare the dc noise signals from the two channels. When these signals are comparable, U106C and U106D direct analog switches U103C (Channel A) and U103B (Channel B) to allow both channels to pass through. The signals from each channel are correlated while the noise is uncor­related, which makes possible a theoretical signal-to-noise improvement of 3 dB. When the dc noise signals are not comparable, the channel with less noise is chosen.
U106A imposes an additional criterion on Channel A, and U106B does the same for Channel B. Each channel’s dc noise voltage is compared to a threshold set by user-adjustable R112 (Squelch). A channel whose noise exceeds this threshold is squelched. If both channels exceed their thresholds, the audio out­put of the receiver is squelched. Squelching is accomplished by tying together the outputs of U106A and U106C (Channel A) or U106B and U106D (Channel B). These outputs also control the yellow “Diversity” status indicators. Compara­tor U102 provides additional attenuation in the squelched state by shutting off compandor U3.
Audio Output
“Peak” LED
Power
The audio signals from the two channels pass through analog switches U103C and U103D, are buffered by U109A, and enter U3, which provides a 2:1 logarithmic expansion. An additional IC amplifier (U109D) operates in conjunction with U3 to provide a lower noise floor. The output of this stage passes through the Volume control (R126) to the “Output” connector (J101). A bridging amplifier formed by U109B and U109C provides the “Balanced Low Z” output.
This red indicator warns the user when the transmitter deviation is approach­ing the limit of 15 kHz. This function is implemented by a window comparator (U102C and U102D) and a pulse stretcher (U102B) that makes short transients more visually apparent.
The green “Power” LED indicates when the external power converter (or a battery pack) is supplying power to the receiver. The circuitry operates normally with an input of 12–18 Vdc. D10 provides reverse polarity protection, and U101 supplies voltage regulation. The “Dc Input,” audio “Output,” and “Balanced Low Z” output connectors are filtered to prevent local oscillator radiation from the cables.
25C1020 (EA)
3 Characteristics
Shure T4 Diversity Receiver
Notes
4Notes
25C1020 (EA)
Preliminary Tests
Listening Tests
Before disassembling the unit, operate it to determine whether it is function­ing normally. First and most important: Review the customer’s complaint (if avail­able) and focus your tests on the problem. If this proves inconclusive or you want somewhat more extensive checks, perform the following functional tests.
Functional Tests
The following tests require partial disassembly of the unit:
RF Test
The following is the best “fast” test of a receiver’s RF performance. A receiv­er that passes this test can be removed from the list of suspects for any “drop­out” or “range” problem.
Initial Set-up
1. Set the receiver’s Squelch control to its middle position and the Volume control to its maximum position.
Shure T4 Diversity Receiver
Audio Tests
2. Set the RF signal generator to the receiver’s frequency.
3. Remove the receiver’s antenna (see “Disassembly,” page 7). Plug the
BNC end of the 50 Ω test cable into the RF signal generator. Tack-solder
the cable’s center conductor to the receiver’s antenna input (TPA1 or
TPB1), and the shield to a ground plane as close as possible to the an-
tenna input (TPA2 or TPB2).
Test
1. Connect power to the receiver and turn it on.
2. Verify that the unit unsquelches with RF signals greater than –89 dBm.
3. When the unit unsquelches, verify that the “Diversity” LED glows.
Initial Set-up
1. Set the RF generator as follows:
Level: –60 dBm Deviation: 15 kHz Modulation: Ext
2. Set the audio analyzer as follows:
25C1020 (EA)
Amplitude: 1.4 V Frequency: 1 kHz
3. Using a 3.3 kΩ load, connect the receiver’s unbalanced audio output to the input of the audio analyzer, and engage the 400 Hz and 30 kHz fil-
rms
5 Preliminary Tests
Shure T4 Diversity Receiver
ters. The receiver’s Volume control should still be in its maximum posi­tion.
Tests
1. Verify the following receiver measurements:
Units that Pass
S Audio level is 400 mV
reference level for the next two steps.
S Thd is <0.75%.
2. Change the audio analyzer’s frequency to 100 Hz, and disengage the audio analyzer’s 400 Hz filter. Verify that the receiver’s unbalanced audio output is within +2 dB, –1 dB of the reference level recorded in step 1.
3. Set the audio analyzer’s frequency to 10 kHz. Verify that the receiver’s unbalanced audio output is –7.5 dB to –10.5 dB of the reference level recorded in step 1.
4. Model T4V only: Place a 150 Ω load across the receiver’s balanced out­put, then connect this output to the audio analyzer. Verify that the output is 65 mV
5. If you are finished testing the receiver, remove the test cable and rein­stall the antenna (see “Reassembly,” page 8).
If the receiver passes these tests, then it is functioning as expected and shouldn’t require alignment. If you did not use the customer’s microphone trans­mitter for these tests, check it for proper operation. If it also checks out of it it was not sent in with the receiver, inform the customer that the product has retested within specifications.
, "15 mV. Remove the 150 Ω load.
rms
, "90 mV. Record your measurement as a
rms
6Preliminary Tests
25C1020 (EA)
Shure T4 Diversity Receiver
Disassembly and Assembly
To access the printed circuit (pc) board, disassemble the receiver.
CAUTION
Observe precautions when handling this static-sensitive device.
Disassembly
1. Disconnect all power to the receiver.
2. Collapse the antennas and rotate them until they lie flat against the case. Place the receiver upside down. Remove and set aside the four screws securing the bottom of the case (Figure 2).
Case mounting screws
Antenna mounting screw
Figure 2. Bottom View of Case
3. Place the receiver in its normal operating position and rotate the anten­nas to their vertical positions. Note that an adhesive-backed nameplate at the at the rear of the unit holds the upper and bottom parts of the case together. To open the case, carefully separate the upper part from the bottom part at the front of the unit. Carefully swing the bottom part of the case away until the two halves are at a 90° angle, to allow removal of the circuit board and antennas (Figure 3).
4. After the circuit board has been removed, pull off and retain the Volume knob.
Volume knob
Case mounting screws
Antenna mounting screw
25C1020 (EA)
7 Disassembly and Assembly
Shure T4 Diversity Receiver
Circuit board
Volume knob
Antenna
Case top
Case bottom
Mounting screw
Figure 3.
Reassembly
1. Slide the Volume knob back on: note how it is keyed to the flat part of the shaft.
2. Rotate the antennas to their vertical positions. Place the pc board, com­ponent-side up, inside the top half of the case: after feeding the anten­nas through their holes, make sure the notches in the case align with the Volume knob, the LEDs align with the holes in the upper half of the case, and that the board is fully seated on the studs.
3. Swing the two halves of the case together until they snap in place.
4. Rotate the antennas until they lie flat against the case. Turn the receiver upside down and secure the assembly with the four screws removed earlier (Figure 2, page 7). Check that the Volume knob rotates freely.
Antenna Replacement
The antennas can be replaced without disassembling the case. Rotate the antenna you are replacing to its vertical position, collapse it, and remove the mounting screw through its access hole in the bottom of the case (Figure 2). In­sert the new antenna and start the screw from the bottom, leaving it loose enough for you to rotate the entire antenna between your fingers. Rotate the an­tenna in this way as you lightly press it into the case until you feel the base seat in the slot of the bracket on the pc board. Tighten the screw.
8Disassembly and Assembly
25C1020 (EA)
Service Procedures
Reference Material
The Shure Wireless System T Series User’s Guide provides a description of the unit as well as operating instructions, troubleshooting suggestions, and tech­nical data.
Special Equipment and Tools
In addition to the standard items described in the Service Equipment manual, you will need:
S a wireless microphone with the same frequency (usually a T1, T2, or
T11) to verify that the receiver is working properly
S an audio amplifier with a high-impedance input (w10 kΩ) and a
monitor speaker, for listening tests
System Operating Frequencies
Each receiver’s circuit board has a resistor next to the group letter (A–H, J–L) that identifies the range of frequencies on which the receiver can operate (see Figure 4). Table 1 shows the Group Letter and its associated frequencies. Note that this chart applies only to T4 receivers.
Shure T4 Diversity Receiver
Table 1
Pc Board Groups
Group Frequency Range
A 169.000–173.975 MHz B 174.000–179.975 MHz C 180.000–185.975 MHz D 186.000–191.975 MHz E 192.000–197.975 MHz
F 198.000–203.975 MHz G 204.000–209.975 MHz H 210.000–215.975 MHz
J 216.000–222.975 MHz
K 223.000–229.975 MHz
L 230.000–237.975 MHz
Tables 2 and 3 provide information for identifying the system frequency. The Crystal Code, together with the appropriate Shure model number, identifies a specific operating frequency for transmitters and receivers. Note that, although a Crystal Code always designates a specific frequency, it may be used with differ­ent Group Letters on other products.
25C1020 (EA)
9 Service Procedures
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