Shure u2 Service Manual

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

UHF Wireless System

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

22 22

INSERT

these Revised pages into the

U2 Service Manual

E2000 Shure Incorporated Printed in U.S.A.
25–1022–2 (AG)

Service Manual

U2 Hand-Held UHF Transmitter

General

Characteristics

The Shure Model U2 Hand-Held UHF Transmitter is a micro­processor controlled microphone-transmitter operating in the 774 to
862 MHz frequency range. This product is intended for use in high­end installed sound, rental, and concert sound applications. Different
frequency variations are available in various countries.

Controls and Indicators

1

2

3

5

4

5

ON

OFF

6

1. Grille

2. Programmable Display

3. Battery Fuel Gauge

4. Battery Cover

5. ON/OFF Switch

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: Operation may require a user license. Frequency or power-output modifications may
violate this product’s approvals. Contact your country’s communications authorities.

7

8

6. Antenna

7. Battery Compartment

8. MODE Button

9. SET Button

10. Audio Gain Control

9

10

GAIN

E1999, Shure Incorporated Printed in U.S.A.
25B1022 (AG)

Shure U2 Hand-Held UHF Transmitter

Circuit Description

Audio Section

Audio enters L248, an inductor used as an rf choke. The signal is
ac-coupled thr ough C201 into a 26 dB user-adjustable gain stage around
U201B. This gain stage is ex t ernally 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 amplif ied audio signal is then passed through a pre-emphasis
network before entering the com pr ess ion stage. R230, R202, and C203
set up two corners for the pre-emphasis network . The pre-emphasis
boosts the high frequencies befor e tr ansm ission.

This network feeds an NE575 compandor, U203, whic h utilizes an
external amplif ier U204B. The compandor perf orm s 2:1 logarithm ic com­pression 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 pr ov ides a stable, cont inuous 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 trans m itt ed signal; there ­fore, if the tone key or the transmit t er 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 cont rolled 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 am plif ier
used to multiply the 3V battery voltage up to 4.5 V (gain = 1.5). As the
battery volt age drops, the tone key supply voltage drops, decr easing
the amplitude of the oscillator. This is used to detect low battery in the
receiver. (This featur e was eliminat ed 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 pre­vent spurious oscillations from the operational amplifier. Aft er passing
ac-coupling capacit or 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 mod­els, 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-

Circuit Description 25B1022 (AG)2

Shure U2 Hand-Held UHF Transmitter

ence from external rf fields. Regulated 5 Vdc power from the dc/dc con­verter 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 synthes iz er’s internal circuitry divides the signal as necess ar y to
the desired ref erenc e frequency of 125 kHz. The synthesizer contains a
quartz-controlled reference oscillat or cir cuit operating from a 4.0 MHz
crystal, Y203, that is adjusted by means of trim m er VC201.

The transmit t er out put fr equency 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 select ion
is made via microproc ess or U104, which interfaces with the user through
the mode/selec t 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 cont rol voltage signal. The contr ol voltage signal is
then connected to the VCO through amplifier U210A which is used to
isolate the PLL filter from the audio modulat ion signals.

The VCO output is also coupled to an rf power resistive pad consist­ing 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 transmit t er is capable of delivering +10 dBm (10 mW ), maxi­mum to the 50 Ω helical antenna. During transm it ter power up and fre­quency select ion, the rf power is muted by bringing the base of Q209
high. This pr ov ides approximately 45 dB rf at t enuat ion until the PLL has
locked.

The transmitter rf is then unmuted by bringing the base of Q209 low.
During transmitt er power off conditions, volt age is first rem oved from the
VCO by bringing the base of Q208 high. In this way, the transmit ter
carrier signal is not allowed to drift off frequenc y during power on or
power off condit ions .

U2 Display Board

The Display Board consists of following circuitry blocks:

Microcontroller Section

The microcont roller section consist s of microcontr oller U104 and the
liquid crystal display (LCD). The microcontroller has an on-boar d LCD
driver. R104, R105, and R107 supply the microcontroller wit h the LCD
drive voltage for a 4- plex drive.

The LCD indicates the UHF frequency group and channel, and also
has a batt ery fuel gauge. A 4. 000 MHz oscillator, Y101, pr ovides the

Circuit Description25B1022 (AG) 3

Shure U2 Hand-Held UHF Transmitter

operating frequency to the microcont roller. The oscillat or cir cuit inc ludes
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 res ist or 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 com­patible 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 micro­controller 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 interf ace section consists of power, MODE, and SET
switches. The LCD provides the user with feedback for all switch
operations.

Circuit Description 25B1022 (AG)4

Preliminary Tests

Test Component Locations

TOP

Shure U2 Hand-Held UHF Transmitter

BOTTOM

DIGIT AL DISPLAY BOARD

BOTTOM

R227 location for G and
later board versions.

TOP

R227 location for F and
earlier board versions.

RF-AUDIO BOARD

Figure 2. Test Component Locations

Preliminary Tests25B1022 (AG) 5

Shure U2 Hand-Held UHF Transmitter

Listening Test

Before completely disassembling the transmitter, operate it to deter­mine whether it is functioning normally and try to duplicate the reported
malfunction. Refer to the User Guide for operating instructions, trouble­shooting, 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.

Preliminary Tests 25B1022 (AG)6

Shure U2 Hand-Held UHF Transmitter

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 measure­ment 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 measure­ment from the U4 unbalanced output is within ± 1.5 dB with
respect to the 1 kHz level.

Preliminary Tests25B1022 (AG) 7

Shure U2 Hand-Held UHF Transmitter

Notes

This page intentionally left blank.

Notes 25B1022 (AG)8

Shure U2 Hand-Held UHF Transmitter

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 complet ing all repairs, slide the circuit boar ds back into the
case; then reinstall the retaining ring, sc rew and microphone
head.

MICROPHONE

HEAD

RETAINING RING

PRINTED CIRCUIT BOARD ASSEMBLY

BATTERY NEST

RF GROUND

SCREW

CASE

CONDUCTIVE WASHER

ANTENNA

“O” RING

BATTERY

CUP

Figure 3. U2 Transmitter Disassembly and Assembly

Disassembly and Assembly25B1022 (AG) 9