Shure U2 User manual

Shure Incorporated
222 Hartrey Avenue
Evanston IL 60202-3696 U.S.A.
UHF Wireless System
E2000 Shure Incorporated Printed in U.S.A.
25–1022–2 (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.
These 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 SERVICE MANUAL REVISION HISTORY
Release Part Number Date Code
Original 25A1022 QE
Revision 1 25B1022 SA
Revision 2 25C1022 TD
Revision 3 25C1022 AG
CHANGES EFFECTIVE JULY 2, 2001
REMOVE
these pages from the
U2 Service Manual
INSERT
these Revised pages into the
U2 Service Manual
22 22

E1999, Shure Incorporated Printed 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 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
4GAIN
2
6
3
7
1. Grille
2. Programmable Display
3. Battery Fuel Gauge
4. Battery Cover
5. ON/OFF Switch
6. Antenna
7. Battery Compartment
8. MODE Button
9. SET Button
10. Audio Gain Control
Figure 1. U2 Transmitter Controls and Indicators
ServiceNote: 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.

Shure U2 Hand-Held UHF Transmitter
Circuit Description 25B1022 (AG)2
Circuit Description
Audio Section Audio enters 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-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.
This 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, along 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 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 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 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, is 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 kHz
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. 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-

Shure U2 Hand-Held UHF Transmitter
Circuit Description25B1022 (AG) 3
ence 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 output of the VCO is coupled by C207 to the frequency
control pin of synthesizer U205.
The synthesizer’s 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
crystal, 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 interfaces 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 amplifier 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 fixed 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 filter 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 Ωhelical antenna. During transmitter power up and fre-
quency selection, the rf power is muted by bringing the base 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
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 microcontroller 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 Transmitter
Circuit Description 25B1022 (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 is the pull-up resistor for the
U104 programming voltage pin.
Memory Section The memory section consists of U101, a non–volatile 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 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 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 Section
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-AUDIO 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 Tests 25B1022 (AG)6
Listening Test Before completely disassembling the transmitter, operate it to deter-
mine whether 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, functional
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 voltages 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 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 positive (+) 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 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 analyzer’s 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 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
respect to the 1 kHz level.

Shure U2 Hand-Held UHF Transmitter
Notes 25B1022 (AG)8
Notes
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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 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 repairs, 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 Assembly

Shure U2 Hand-Held UHF Transmitter
Notes 25B1022 (AG)10
Notes
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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 experience 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 tuning voltage of the VCO will read 0 Vdc.
Adjusting the crystal’s 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, once the unit is turned off, the problem may
return.
All units with August 1996 date codes or later have a 10 kΩresistor
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 16.8 to 33.2 kΩ.

Shure U2 Hand-Held UHF Transmitter
Service Procedures 25B1022 (AG)12
Antenna Replacement
The top printed circuit board (pcb) is connected to the bottom pcb by
a multi–pin connector. Two wires also lead to the battery connector and a
three-wire flat cable that connects the pcbs to the microphone 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 sure that the washer on the antenna clears the case.
8. Install the new antenna by screwing it onto the connector. If
necessary, replace the conductive rubber gasket at the base
of the antenna.
9. Return the pcbs to their original position.
10. Reinstall the single screw next to the antenna connector.
11. Perform these steps in reverse order to reassemble the unit.

Shure U2 Hand-Held UHF Transmitter
Service Procedures25B1022 (AG) 13
Test Equipment
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 =2.2 dBu
0 dBu =0 dBm, assuming the load = 600 Ω
Table 1
Test Equipment
Equipment Type Model
Audio analyzer *Hewlett-Packard 8903B
Digital multimeter Fluke 87
Rf signal generator Hewlett-Packard 8656B
Frequency counter Hewlett-Packard 53181A
Spectrum analyzer Hewlett-Packard 8590L
Shure U4 receiver Shure U4
SMC to BNC Adapter PT1838S
Audio Test Head PT1840
Test Head Brass Ring PT1838Y
*Audio levels in dBu are marked as dBm on the HP8903B.
Reference Material
Use the Shure UHF Wireless System User’s Guide for information
on Controls, Operation, Specifications, etc. Refer to the appropriate
User’s Guide or User’s Guide Supplement for information on frequency
compatibility.

Shure U2 Hand-Held UHF Transmitter
Service Procedures 25B1022 (AG)14
Test Set-Up 1. Use a UA802 0.61 m (2 ft) coaxial cable or an RG58 low-loss
50 Ω cable for all cable connections.
2. Include the insertion loss of the cables and connectors in rf
conductive power measurements.
3. Audio gain potentiometer R208 does not need to be preset;
however, on JB models, GAIN should be set to maximum.
4. All rf measurements should be made through 50ΩSMC
connector J103.
5. Proper adapters should be used to connect the test equipment.
6. Apply 3.0 Vdc from a dc power supply to the respective U2
battery terminals.
7. Turn on the U2 by switching S101 to the ON position.
Output Power Confirmation
1. Using the spectrum analyzer, verify output power is at least
+8 dBm. JB models must have at least +8 dBm, but cannot
exceed +10 dBm.
2. Rf output power is not adjustable.

Shure U2 Hand-Held UHF Transmitter
Service Procedures25B1022 (AG) 15
Rf Alignment
VC201
J103
FREQUENCY COUNTER
U2 Transmitter Frequency Counter
Power (S101): ON Connect CH2: J103
Gain: For JB models:
set to maximum
Figure 4. Rf Alignment Configuration
1. Verify that the transmitter is ON; switch S101 is set to the
ON position.
2. Connect the transmitter to the frequency counter via J103.
3. Determine the transmitter operating frequency by comparing the
group and channel information on the LCD to the tables in the
User’s Guide and User’s Guide Supplements.
4. Adjust variable capacitor VC201 until the frequency counter
measurement matches the desired frequency, ±1 kHz, found in
the User’s Guide and User’s Guide Supplements.

Shure U2 Hand-Held UHF Transmitter
Service Procedures 25B1022 (AG)16
Audio Alignment
Deviation Reference Voltage
S201 (INSIDE U4)
U4 RECEIVER
RF SIGNAL GENERATOR AUDIO ANALYZER
DC
BLOCK
U4 Receiver Audio Analyzer Rf Signal Generator
Output: Unbalanced Measurement: AC level INT: FM
Gain: Maximum Filters: INT: 1 kHz
Squelch: Mid Low-Pass (30 kHz): ON Output Amplitude: –50 dBm
Tone Key (S201): OFF High-Pass (400 Hz): ON
Figure 5. Deviation Reference Voltage Set-Up
1. Turn the U2 transmitter OFF.
2. Remove the cover of the U4 receiver to expose the pcbs.
3. Connect the rf signal generator to antenna port A or B on a U4
receiver. Make sure the dc block is on the rf signal generator.
4. Set the rf signal generator to the same frequency as the U2.
5. Set the rf signal generator internal FM tone to 1 kHz modulation.
6. Set the rf signal generator deviation to 45 kHz for UA, UB, MA,
MB, MC, and MD models; 40 kHz for KK models; and 5 kHz for
II models.
7. Set the rf signal generator amplitude to –50 dBm.
8. Turn the U4 receiver ON and set switch S201 inside the U4 to
the OFF position. This will disable the tone key function.
9. Set the output level of the U4 receiver to maximum.
10. Connect the voltmeter section of the audio analyzer to the
unbalanced output of the U4.
11. Verify that the voltage is 4.2 ±0.5 dBu (1.26 ±0.07 V) for UA, MA,
UB MB, MC, MD, and KK models, and –26.2 ±0.5 dBu for II mod-
els. This is the deviation reference voltage.
12. Disconnect the rf signal generator from the U4 and move switch
S201 on the U4 to the ON position.
13. Turn OFF the rf output power from the rf signal generator.

Shure U2 Hand-Held UHF Transmitter
Service Procedures25B1022 (AG) 17
Deviation Reference Voltage Adjustment
R286
U4 RECEIVER
AUDIO ANALYZER
TEST HEAD RETAINING
RING
DC
BLOCK
20 dB
PAD
U201 U204 R227 for
G and later
board ver-
sions
R227 for
F and earlier
board versions
U2 Transmitter Audio Analyzer
Power: +3 Vdc Measurement: AC level
Gain: Minimum; for JB models set to MAX Output: 1 kHz
Filters:
Low-Pass (30 kHz): ON
High-Pass (400 Hz): ON
Figure 6. Microphone Test Head Configuration
1. Slide the U2 circuit boards into the supplied test head retaining
ring assembly.
2. Attach the microphone test head to the test head retaining ring
assembly.
3. Connect the audio analyzer output to the microphone test head
input. Connect the shield probe to the audio analyzer’s input.
4. Turn the U2 transmitter ON.
5. Adjust the audio analyzer output for 1 kHz to achieve a level of
-5.0 dBu (436 mV) at pin 7 of U201 on the transmitter. For JB
models, adjust the audio analyzer for 1 kHz and -65 dBu at the
input of the test head.
6. Connect the transmitter rf output to an antenna port on the U4
through a dc block and a 20 dB pad.
7. Connect the U4 unbalanced output to the audio analyzer’s input.
8. Adjust R227 until the audio analyzer reads the deviation
reference voltage determined in the previous test, ±0.05 dB
(±0.2 dB for JB models).
9. Disconnect the audio analyzer from the U4 unbalanced output.

Shure U2 Hand-Held UHF Transmitter
Service Procedures 25B1022 (AG)18
Tone Key Level Adjustment
1. Use a dc power supply to apply 2.5 ±0.01 Vdc to the
battery terminals.
2. No audio is applied to the audio input.
3. Do not use filters on the measuring instrument.
4. The tone key frequency will be approximately 32.768 kHz.
5. Adjust R286 so that a tone key level of -22.8 ±0.1 dBu (56 mV)
is measured at pin 1 of U204. For JB models, this level is
–24.7dBu ±0.1 dBu (45 mV).

Shure U2 Hand-Held UHF Transmitter
Bench Checks25B1022 (AG) 19
Bench Checks
Dc Problems
nVerify the battery voltage is between 2 and 3.5 V.
nCheck for proper Vcc and +5 V rf at Q208 (make all dc measure-
ments with respect to rf ground unless otherwise specified). if
incorrect voltage is present, check the biasing resistors values.
nTrace the dc back to the dc to dc converter.
nCheck the power switch.
nLook for open coils, cracked parts, reversed polarity capacitors,
solder shorts. if there is a short to ground from 5 V, isolate differ-
ent parts of the circuit.
nVerify rf OFF signal changes from +5V at power up/power down
to 0V during normal operation. Trace the signal to the micropro-
cessor. Q208 should be saturated during normal operation.
nVerify that battery voltage appears at U208, pin 1. Check for
reversed polarity capacitors C239 and C247.
nVerify Vds of Q204 is approximately –.025 V. Q204 should be
saturated.
nVerify 5V dc/dc converter output at U208, pin 8. Check for open
coil L205, reversed polarity or bad diodes D201 and D202, or
bad converter U208.
Rf Problems
nIf the carrier is out of specification by less then 40 kHz and
cannot be corrected by adjusting VC201, check the values of
VC201, C224 and Y203. If these values are correct, replace
Y203. As a last resort, replace synthesizer U205.
nIf the carrier frequency is not between 782 and 810 MHz, or is
unstable, the loop is unlocked. Check the solder connections at
the, head board, VCO, microprocessor (traces LE, D, and CK)
and synthesizer U205.
nCheck for 4 MHz oscillation at pins 1 and 2 of U205. if not
replace the crystal Y203.
nCheck the values and polarity of the loop filter: R226, C231,
R251, C237, R243, C257 U210, R227, and R270.
nCheck the bias voltage of U205 pins 3 and 4 and U210, pin 8.
nAs a last resort, replace synthesizer U205. The tuning voltage
of the VCO should be about 3 Vdc when the transmitter is pro-
grammed for 800 MHz operation.