Shure Т2 User Manual

Shure Incorporated 222 Hartrey Avenue Evanston IL 60202-3696 U.S.A.

T Wireless System

SERVICE MANUAL CHANGE NOTICE

T2 WIRELESS HANDHELD TRANSMITTER

Changes and c orrections h ave b een m ade t o t he S ervice M anual f or t he T 2 h andheld Transmitter. To update your Service Manual, remove the pages identified in the tables below and replace them with the pages attached to t his C hange N otice. N ote t hat t here a re n o c hanges t o p ages n ot s pecifically i dentified i n the t ables below.

T2 HANDHELD TRANSMITTER SERVICE MANUAL REVISION HISTORY

Release Part Number Date Code Color

Original 25A1018 QH White Revision 1 25B1018 SB Pink Revision 2 25C1018 SI White Revision 3 25C1018 TF White Revision 4 25C1018 TL White Revision 5 25C1018 AF White Revision 6 25C1018 BA White

Revision 7 25C1018 CC Red

CHANGES EFFECTIVE MARCH 17, 2003

REMOVE

these pages from Revision the

T2 Service Manual

these new Revision pages into the

INSERT

T2 Service Manual

31 & 32 31 & 32

E1999, Shure Incorporated Printed in U.S.A. 25–1018–1 (CC)

T2 Vocal Artist Microphone-Transmitter

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Service Manual

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Characteristics

General

This section tells how to service and align the Shure Vocal Artist T2 Microphone-Transmitter (Figure 1). The single-channel, crystal-controlled transmitter operates in the 169 MHz to 216 MHz (FCC-approved models) or 173–240 MHz (ETSI-approved models) VHF band. (The differences between the two versions of this product are explained on the next page.)



E1999, Shure, Inc. Printed in U.S.A.

Figure 1.

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 product’s approvals.

Contact your country’s communications authorities.

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Characteristics

Shure T2 Vocal Artist Microphone Transmitter

Circuit Description

This unit contains two interconnected circuit boards that comprise the audio and RF sections, respectively. It is intended for use with the matching T3 and T4 receivers.

FCC-Approved vs. ETSI-Approved Models: Models approved by

the Federal Communications Commission (assembly number 90–8690, with boards marked 34A8494) have different sections from those approved by the European Telecommunications Standards Institute (assembly number 90–8705, with boards marked 34A8538). The FCC-approved version, sold in North America and many other places, uses only the frequencies listed in Table 3 on page 12. The ETSI-approved version, sold in Europe and many other places, uses only the frequencies listed in Table 4 on page 13. Hence, the following circuit descriptions have separate sections for the two RF boards. The audio sections are the same for all T2 models.

Audio Section

Input: The microphone element converts the sound source into an electrical signal, which then enters the audio board through the center contact of the head board (Figure 5, page 16).

Preamplifier Stage: This is centered in one section of operational amplifier U102C. Externally accessible potentiometer R175 adjusts the voltage gain of this stage over a 25 dB range.

Passive Pre-emphasis Network and Compandor: The network (R145, C110, C111, C112, and R115) has a pole at 63 microseconds and a zero at 12 microseconds. The NE571D integrated circuit compander (U101A) provides 2:1 logarithmic compression of the audio signal.

Noise, Distortion, and Limiting: U102A lowers the noise floor, and internal potentiometer R130 nulls the system audio distortion. Operational amplifier U102B, operating as a two-pole, active low-pass filter, restricts the bandwidth of the system to the audio frequencies. PNP transistors Q103 and Q104 limit the level of the audio signal leaving the audio section via U102B.

5 Vdc Bias and LED Drive Circuits: The NE571D’s identical second channel (U101B) supplies regulated, low-noise 5 Vdc bias to various audio and RF circuit points. Transistor Q105 provides “reverse battery protection” to the circuit. Q106 drives LED D101 (“Power 0n”), and Q107 drives LED D102 (“Low Battery”).

RF Section: FCC-Approved Models

Audio Input: Processed audio enters R217, an internal potentiom-

eter that is adjusted for 15 kHz deviation (100% modulation) when the audio section provides a –2.2 dBV, 1 kHz tone.

Characteristics

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Shure T2 Vocal Artist Microphone Transmitter

20 MHz region. Fundamental-mode crystal Y201 is tuned 10 kHz below series resonance by the series combination of frequency-netting coil L209, diode D201, capacitor C214, and capacitor divider C224 and C230.

Frequency and Temperature Stability: To ensure frequency stability despite changes in the battery voltage, regulated 5 Vdc bias is applied to the varactor diode and to the base of Q201. C224, C230, and C214 provide temperature compensation.

Tuned Circuits (FCC-Approved Models)

Stage 1: The collector circuit of Q201 is tuned to the third harmonic

of the oscillator frequency (approximately 60 MHz) by L205, C225, C234, L202, C217, C237, and C233. (The latter components also form a capacitively tapped voltage divider for matching into the base of Q203.) The output is double-tuned to provide high spectral purity. Regulated dc bias is again employed to minimize changes in loading on the oscillator stage and to stabilize the drive levels.

Stage 2: Q203 operates as a frequency tripler, with the collector circuit tuned to the output frequency (for example, 180 MHz). In this case, L204, C216, C238, C236, L210, C235, and C222 perform tuning and impedance-matching functions. As in the preceding stage, regulated dc bias is applied to the base circuit to stabilize the drive level, and the output is double-tuned to provide spectral purity.

Stage 3: Q204 operates as a tuned amplifier. Resistive loading on the input provides stability. The output circuit consists of a resonant tank circuit (L203 and C213) capacitively coupled to a low-pass filter (C219, L206, and C218). C213 and C219 provide a capacitively tapped voltage divider for matching into the low-pass filter.

Final Output (FCC-Approved Models)

Transmitter: This can deliver up to +17 dBm (50 milliwatts) to the

antenna. No user adjustments permit this value to be exceeded. Testpoint I110 provides a termination point for the 50 Ω output. C211 and L207 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 like the Duracell MN1604 is recommended).

Voltage Measurements: With 9 Vdc applied to the unit, the following voltages should appear at the terminals of the output transistor:

S Vc = 8.88 Vdc

S Vb = .450 Vdc

S Ve = .473 Vdc

S Base current = 0.29 mAdc

S Emitter current = 21.5 mAdc

S Collector current = 21.8 mAdc

S Power input = 183 mW

25C1018 (CC)

Characteristics

Shure T2 Vocal Artist Microphone Transmitter

The output power is +16.5 dBm (44.7 mW) into a 50 Ω load, at a frequency of 169.4445 MHz. At the lowest acceptable battery voltage of 6 Vdc, the final collector current drops to 15 mAdc and the output power to +13.9 dBm (24.4 mW).

Spurious Emissions: To minimize the production and radiation of spurious emissions and harmonic energy, and to promote stable operation, the collector of each RF stage is separately decoupled from the 9 V supply by ferrite chokes, resistors, and bypass capacitors. The base circuits are similarly decoupled except they use resistor-capacitor (R-C) networks, whose higher-impedance levels are more appropriate.

RF Section: ETSI-Approved Models

Audio Input: Processed audio enters R201, an internal potentiom-

eter 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 baseemitter circuit 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 and Temperature Stability: To ensure frequency stability despite changes in the battery voltage, regulated 5 Vdc bias is applied to the varactor diode and to the base of Q201. C203, C206, and C207 provide temperature compensation.

Tuned Circuits (ETSI-Approved Models)

Stage 1: The collector circuit of Q201 is tuned to the third harmonic

of the oscillator frequency (approximately 60 MHz) by L202, C208, C244, C210, L203, C214, C213, and C215. (The latter components also form a capacitively tapped voltage divider for matching into the base of Q202.) The output is double-tuned to provide high spectral purity. Regulated dc bias is again employed to minimize changes in loading on the oscillator stage and to stabilize the drive levels.

Stage 2: Q202 operates as a buffer, with the collector circuit tuned to the output frequency (for example, 60 MHz). In this case, L204, C216, C245, C218, L205, C222, C221, and C224 perform tuning and impedance-matching functions. As in the preceding stage, regulated dc bias is applied to the base circuit to stabilize the drive level, and the output is double-tuned to provide spectral purity.

Stage 3: Q203 operates as a frequency tripler, with the collector circuit tuned to the output frequency (for example, 180 MHz). In this case, L206, C226, C227, C229, L207, C230, and C232 perform tuning and impedance-matching.

Characteristics

Stage 4: Q204 operates as a tuned amplifier. Resistive loading on the input provides stability. The output circuit consists of a resonant tank

25C1018 (CC)

Shure T2 Vocal Artist Microphone Transmitter

circuit (L203 and C213) capacitively coupled to a low-pass filter (C219, L206, and C218). C213 and C219 provide a capacitively tapped voltage divider for matching into the low-pass filter.

Final Output (ETSI-Approved Models)

Transmitter: This can deliver up to +11.5 dBm (14 milliwatts) 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 like the Duracell MN1604 is recommended).

Voltage Measurements: With 9 Vdc applied to the unit, the fol-

lowing voltages should appear at the terminals of the output transistor:

S Vc = 8.83 Vdc S Vb = .097 Vdc S Ve = .32 Vdc S Base current = 0.27 µAdc S Emitter current =9.67 mAdc S Collector current = 9.67 mAdc S Power input = 87 mW

The output power is +9.5 dBm (8.9 mW) into a 50 Ω load, at a frequency of 169.4445 MHz. At the lowest acceptable battery voltage of 6 Vdc, the final collector current drops to 8.84 mAdc and the output power to +7.3 dBm (5.4 mW).

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Characteristics

Shure T2 Vocal Artist Microphone Transmitter

Notes

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Preliminary Tests

Listening Tests

Before disassembling the unit, operate it to determine whether it is functioning normally.

Focused Testing: First and most important: Review any customer complaint or request and focus your tests on any reported problem for both listening and functional tests. For example, many complaints are for “short range” and “drop-outs.” In such cases, perform only the RF tests in this section to verify the problem. If the unit passes these, there is a strong indication that the customer is using the product incorrectly (e.g., not keeping the transmitter in the receiver’s line of sight, not avoiding metal enclosures or TV interference). Return the unit to the customer together with an explanation of the proper set-up procedures.

Functional Test

For complaints of distortion or other audio problems, try a “standard” microphone cartridge (you should have one of each cartridge on-hand for testing) and perform the audio tests in this section.

Shure T2 Vocal Artist Microphone Transmitter

RF Tests

Note: Most of the following tests can be performed without disassembling the unit.

1. Install a fresh 9 V battery in the T2, mute its audio, and turn it on.

2. Measure current drain: it should not exceed 35 mA.

3. Maximize the signal received on the spectrum analyzer by attaching a telescoping whip antenna to it. Then measure the near-field output power: it should be 7 dBm (FCC-approved model) or 3 dBm (ETSI-approved model).

(If you are unsure of the results you obtained here, measure the output power conductively by soldering a 50 Ω cable to the output of the transmitter. Verify that the output power is 15 dBm, 2 dBm [FCC-approved model] or 10 dBm, 2 dBm [ETSI-ap- proved model].)

4. Verify that the carrier frequency of the transmitter varies from its nominal value by no more than "6 kHz.

5. Check for an intermittent problem by shaking the transmitter and tapping on it. As you do so, try to keep it at a constant distance from the spectrum analyzer. Verify that the output power on the spectrum analyzer shows no large and sudden drops in power level (it will, however, vary a few dB with hand position).

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6. Turn off the T2.

If the transmitter passes the above tests, its RF circuits are

working as designed.

Preliminary Tests

Shure T2 Vocal Artist Microphone Transmitter

Audio Tests

A: Verify the Matching Receiver

1. Make sure that the receiver is turned off. Connect the signal generator to the receiver through a 50 Ω cable. Tack-solder the center conductor to the antenna input and ground the shield of the cable to pcb ground. Turn on the receiver.

2. Set the RF signal generator as follows:

Amplitude: –50 dBm Modulation: 1 kHz Deviation: 15 kHz Frequency: T2 operating frequency

3. Connect the audio from the unbalanced output to the audio analyzer with a 3.3 kΩ load. Turn the Volume control all the way up.

4. Engage the 400 Hz and 30 kHz filters on the audio analyzer. Verify the following:

S For the T3 and T4 the audio level is 400 mVrms ("90 mV) S For the T4N the audio level is 626 mVrms ("120 mV) S thd = <0.75%

B: Check the Transmitter

Units That Pass

good, then the system is functioning as expected and shouldn’t require tuning and alignment. Inform the customer that the product has retested within specifications.

1. Disconnect the signal generator from the receiver. Monitor the receiver’s unbalanced audio output with a 3.3 kΩ load and the audio analyzer. Make sure the receiver’s Volume control is at its maximum setting.

2. Replace the microphone cartridge on the T2 with the test head. Set the unit’s Gain control to minimum and unmute the audio.

3. Inject a 775 mV, 1 kHz signal from the audio analyzer into the adapter cable and verify the following:

S the amplitude from receiver’s unbalanced output equals

400 mVrms ("90 mV)

S thd = <0.75%

4. Change the frequency of the audio generator to 100 Hz and disengage the 400 Hz high-pass filter from the audio analyzer. Verify that the audio level is –1.0 dB ("0.7 dB) relative to the level measured in step 3.

5. Change the frequency of the audio generator to 10 kHz and reengage the 400 Hz high-pass filter. Verify that the audio level, relative to that measured in step 3, is –3.5 dB, "2 dB.

If the system components pass these tests and the microphone is

Preliminary Tests

25C1018 (CC)

Shure T2 Vocal Artist Microphone Transmitter

Disassembly and Assembly

To access the printed circuit (pc) boards, disassemble the transmitter

(refer to Figures 2 and 3 on pages 9 and 10).

CAUTION

Observe precautions when handling this static-sensitive device.

Disassembly

1. Turn off the Power switch.

2. Unscrew the transmitter battery cup and remove the battery.

3. Unscrew the microphone cartridge.

4. If necessary, remove the microphone-transmitter subassembly: (a) Use snap ring pliers to remove the retaining ring from in-

side the microphone handle.

(b) Remove the bezel by carefully inserting a small screwdriver

into the microphone handle, pressing the blade against the plastic bezel tab, and prying it up (Figure 2). Remove the label plate and switch actuators (Figure 3, page 10).

Note: Newer bezels have the labeling printed directly on their faces; there are no separate label plates.

and head circuit boards) from the handle, note how it was positioned in the internal guides.

bezel

handle

tab

(Right-side view)

tab

circuit-board subassembly

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Figure 2. Removing the Bezel

Disassembly and Assembly

Shure T2 Vocal Artist Microphone Transmitter

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Reassembly

1. Insert the transmitter subassembly (audio, RF, and head circuit boards) into the internal guides of the handle (Figure 3).

2. Orient the retaining ring so its gap will fit over the flat edge of the head board (to avoid shorting the board). Use snap-ring pliers to insert the retaining ring into the groove inside the handle.

3. Drop in the switch actuators and position the label plate (older bezels only) over them. Position the bezel over the switches then press until it snaps into place.

4. Screw on the microphone cartridge and ball screen. Install a battery (if desired) and screw on the battery cup.

ball screen

retaining

ball screen

microphone cartridge BG 3.1

ring

circuitboard

head board

Figure 3.

switches

circuitboard guides

microphone cartridge SM 58

audio circuitboard

(older, BG 3.0

gain control

handle

cartridge)

(older bezels only)

label plate

access to gain control

9 V alkaline battery

bezel

battery cup

switch actuators

Disassembly and Assembly

25C1018 (CC)

Shure T2 Vocal Artist Microphone Transmitter

Service Procedures

Reference Material

The Shure Wireless System T Series User’s Guide describes the product, tells how to operate it, and provides troubleshooting and technical data.

Special Equipment and Tools

In addition to the standard items described in the Wireless Service Equipment manual, you will need:

S to verify that the system is working properly, obtain the receiver

with which the transmitter is used (usually a T3 or T4); otherwise, use the modified SC4 receiver described in the equipment manual

S a small flat-blade screwdriver to remove the bezel

S snap-ring pliers to remove and re-insert the retaining ring

S hand-made high-impedance probe (see the Service Equipment

manual)

System Operating Frequencies

Each transmitter circuit board is marked with a group letter that identifies the range of frequencies on which the transmitter can operate. Note that Table 1 applies only to T2 transmitters that are FCC-approved, and Table 2 applies only to T2 transmitters that are ETSI-approved.

Frequency Coverage: Earlier models used the same family of RF boards (with Groups A, B, and C) for all the frequencies offered worldwide at that time. Now there are separate board assemblies for units approved by the ETSI. If you have a frequency from Table 4, you have an

ETSI-approved model; if you have a frequency from Table 3, you have an FCC-approved model.

Pc Board Groups for

FCC-Approved Models

Group Frequency Range

A 169.000–183.975 MHz B 184.000–198.975 MHz C 199.000–215.975 MHz

Used with pcb assembly 90_8690

(pcb marking 34A8494).

Table 1

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Service Procedures

Shure T2 Vocal Artist Microphone Transmitter

Pc Board Groups for

ETSI-Approved Models

Group Frequency Range

A 169.000–173.975 MHz B 174.000–180.975 MHz C 181.000–187.975 MHz D 188.000–194.975 MHz E 195.000–201.975 MHz

F 202.000–208.975 MHz G 209.000–215.975 MHz H 216.000–222.975 MHz

K 216.000–239.975

Used with pcb assembly 90_8705

Tables 3 and 4 provide information for identifying the system frequency. The Crystal Letter Code, when used with the appropriate Shure model number, identifies a specific operating frequency for both transmitters and receivers. Note that, although a Crystal Letter Code always designates a specific frequency, it may be used with different Group Letters on other products.

Table 2

(pcb marking 34A8538).

Table 3

T2 System Operating Frequencies for

FCC-Approved Models

Crystal

Group

Used with pcb assembly 90_8690

Code

A V 169.445 A W 171.845 A CA 176.200 A CC 177.600 A CE 182.200 A CF 183.600 B CG 186.200

B CL 192.200 C CQ 202.200 C CV 208.200

(pcb marking 34A8494).

Operating Freq. (MHz)

Service Procedures

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