Shure U4D User manual
Shure Brothers Incorporated
222 Hartrey Avenue
Evanston IL 60202-3696 U.S.A.
UHF Wireless System
E2000, Shure Incorporated Printed in U.S.A.
25–1062–2 (TD)
SERVICE MANUAL CHANGE NOTICE
UHF WIRELESS RECEIVER MODEL U4D
Changes and corrections have been made to the Service Manual for the U4D UHF Wireless Receiver.
These changes will make it easier to properly align the receivers. 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.
U4D SERVICE MANUAL REVISION HISTORY
Release Part Number Date Code
Original 25A1062 QE
Revision 1 25B1062 QK
Revision 2 25C1062 SB
Revision 3 25D1062 TD
Revision 4 25D1062 TL
Revision 5 25D1062 AG
CHANGES EFFECTIVE JULY, 2001
REMOVE
these pages from the U4D Service Manual INSERT
these Revisionpages into the U4D Service Manual
35–40 35–40
E1999, Shure Incorporated Printed in U.S.A.
25D1062 (AG)
Service Manual
25D1062 (AG)
U4D Dual Diversity UHF Receiver
General
Characteristics
The Shure Model U4D Dual Diversity UHF Receiver is a microprocessor con-
trolled dual diversity receiver operating in the UHF frequency range. This product
is intended for use in high-end installed sound, rental, and concert sound mar-
kets. Different frequency variations are available in various countries.
Controls and Connectors
5
15
14 18
13 16 17 17 181619 15
7
123 568910 11 12
4
7
123 6 8
4
1. MENU Button
2. SELECT Button
3. RF Level Indicators
4. AUDIO Level Indicators
5. Programmable Display
6. + Button
7. –Button
8. Volume Control
9. Headphone Monitor Volume Control
10. Headphone Monitor Status
11. Headphone Input Connector
12. POWER On/Off Switch
13. Power Input Connector
14. Power Output Connector
15. Antenna Input Connectors
16. HIGH Z (Unbalanced) Output Connector
17. Mic/Line Slide Switch
18. LOW Z (Balanced) Output Connector
19. Networking Interface
Figure 1. U4D Receiver Controls and Connectors
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 U4D Dual Diversity UHF Receiver
2
25D1062 (AG) Circuit Description
Circuit Description
Power Section The receiver accepts power line voltage ranging from 85 Vac to 264
Vac. The receiver hardware uses the +5 Vdc, +12 Vdc and 12 Vdc volt-
ages from the switching power supply. The switching power supply has
40 W overall output power capability, with maximum current capabilities
of 4A at 5V, 2A at +12V, and .5A at –12V. It also includes a fast–acting
2.5A fuse.
Up to four in-line rf amplifiers may be connected to the receiver,
depending on system setup. The receiver provides dc power to the in-
line amplifiers via the BNC antenna ports and RG58 cables. Maximum
dc power supplied to each antenna port is limited by self–resettable fuse.
Rf Section The rf circuit description is limited to one rf strip (channel A) in
receiver 1. The other rf strip (channel B) is virtually identical. The local
oscillator (LO) section is common for both channels and is described
separately. Receiver 2 is identical to receiver 1.
The rf input signals are sent from the antenna ports to the receiver
via cables with BNC and rf mini–plug connectors. Antenna port A is con-
nected to J302 of receiver 1. Antenna port B is connected to J302 of
receiver 2. Connectors J302 on each receiver are the input of the rf
power dividers.
Each of these splits the rf power from the antenna between two
receivers. The outputs of the power dividers are connected to the inputs
of the opposite rf strips of the other receiver: J303 of receiver 1 to J304
of receiver 2; and J303 of receiver 2 to J304 of receiver 1. In addition,
J306 on receiver 1 and J306 on receiver 2 have to be solder jumpered to
provide connection from the outputs of the rf power dividers to channel A
rf strips of both receivers.
Rf Channel The rf signal is preselected to the appropriate frequency range with
two dielectric filters. The first dielectric filter is located between the
antenna port and the low noise amplifier (LNA). The second filter is
located between the LNA block and mixer input. The front end down–
converter integrated circuit contains the LNA block and the first mixer.
The first conversion produces the first intermediate frequency (IF)
signal at 50 MHz. The first if signal is amplified with the MMIC, band-
limited with a SAW filter, then down-converted to the second IF frequen-
cy (10.7 MHz) with a second down-converter.
The second down-converter has an internal second local oscillator
(LO) that oscillates at 60.7 MHz, using an external crystal. The second
LO buffered output also provides the LO drive to channel B of the sec-
Shure U4D Dual Diversity UHF Receiver
3 25D1062 (AG)Circuit Description
ond mixer. The second down–converter also incorporates an internal IF
amplifier that is used with external 10.7 MHz ceramic filters. The 10.7
MHz signal goes to the second IF gain block with detector. The audio
output is buffered with an operational amplifier, then processed as de-
scribed in the Audio section. The noise output is also amplified by the
operational amplifier, providing a signal for the noise squelch circuitry.
The received signal strength indication (RSSI) output of LM1865 is used
to drive the LEDs on the receiver front panel.
Local Oscillator The first local oscillator (LO) is common for channel A and channel B
rf strips. The LO is a phase locked-loop (PLL) system. The PLL consists
of a prescaler/synthesizer, voltage-controlled oscillator (VCO), loop filter,
rf power divider, and band-pass filter, band limiting the LO signal before
injection to the first down converter. The prescaler receives the rf signal
from the VCO via the coupling capacitor, C116. The output from the
phase detector is connected to the external loop filter, which controls the
tuning voltage input to the VCO.
The prescaler/synthesizer integrated circuit (IC) is a serial program-
mable input IC. It receives the programming data from the front panel/
digital board. The digital board includes a user-controlled microprocessor
that allows users to change the frequency and other settings.
Audio Section The audio for channel A comes from the channel A detector output
of the rf section. Each channel’s audio then enters its own factory-adjust-
able gain amplifier stage. These adjustable gain stages are used to
exactly match the audio levels coming from each rf channel, as well as to
set the proper level necessary for the compandor.
From the gain stages, each channel enters an analog switch. Noise
outputs also come from the channel A and channel B detector outputs.
Each noise output enters a bandpass noise filter that is used to measure
the 60 kHz noise present in the audio signal. The noise level is propor-
tional to the signal-to-noise ratio of the channel.
The noise from a channel, after being rectified and low-pass filtered
(changed from an ac to dc signal), enters a bank of comparators. A ver-
sion of the channel’s noise that is 6 dB less also enters the comparator
bank. The noise levels from the two channels are then compared. If they
are within 6 dB of each other, the comparators send a logic high signal to
the control of each channel’s analog switch, and audio is allowed to pass
through the switches.
If the noise levels are not within 6 dB of each other, the channel with
the noise level greater than 6 dB of the other channel is not allowed to
pass through the analog switch; the comparator puts a logic low signal
on the control line for the analog switch. Also, each channel’s noise is
Shure U4D Dual Diversity UHF Receiver
4
25D1062 (AG) Circuit Description
compared to an adjustable squelch level (a dc level). If either channel’s
noise is greater than the squelch threshold, its switch is shut off.
The outputs from the analog switches are connected at the audio
combining stage. This is a unity gain buffer stage where the audio from
channel A is combined with the audio from channel B. The output from
this stage splits into three paths.
The first path goes to a high Q tone key detection circuit. This circuit
is a crystal filter in which the tone key level is converted to dc and
compared to a fixed dc voltage. If the tone key is not present, the
comparator sends a logic high signal to an audio mute IC and mutes
the receiver output. If the tone key is present, a logic low signal is sent,
and the audio is allowed to pass.
The second path goes to a low Q bandpass filter centered around
32 kHz. This filter provides low battery detection in the receiver. The
lower Q allows for small frequency variation of tone key from various
transmitters, without large amplitude variations that the crystal filter
would have.
The filtered signal is then rectified and averaged. The resulting dc
signal is amplified and then enters the digital section of an analog to digi-
tal (A/D) converter. The A/D converter and the microcontroller
control the battery icon on the LCD display.
The third path goes into the compandor, via a 17 kHz low-pass filter.
Here the audio is expanded and de-emphasized. The compandor output
then goes off the audio board to a volume potentiometer on the front
panel board. Then the wiper is brought back to the audio board.
At this point, the audio signal takes two paths. The first path is
through the mute IC and into the output stage. The output stage consists
of an inverting amplifier stage, the output of which goes directly to one
pin of an XLR connector. A 180°phase-shifted version of the same sig-
nal is obtained by tapping off of this point and entering another inverting
stage. This phase-shifted version then goes to another pin on the XLR
connector.
Taking the output across the two XLR pins provides an electrically
balanced output signal. The unbalanced output is obtained by taking one
of the output stage amplifier’s outputs with respect to ground. Each side
of the balanced output goes through a pad that is switched in or out by
the user. This switch changes the balanced output level by approximate-
ly 30 dB.
The second path is through the headphone amplifier circuit. The
audio signal goes into a fixed gain amplifier, then off the board to the
monitor board. The monitor board can select between receiver 1 and
receiver 2. It also has a user-adjustable gain control, and a 1/4 inch jack
for headphones.
For the audio level meter, audio is tapped off from the 17 kHz filter
output and goes through a full wave precision rectifier and averaging cir-
cuit. This dc signal then enters a dc amplifier stage to adjust levels for
Shure U4D Dual Diversity UHF Receiver
5 25D1062 (AG)Circuit Description
the LEDs. The output from this stage drives the audio level meter on the
front panel board.
A dc voltage from the detector chip RSSI drives the bar graph
integrated circuit on the front board for the rf level meters.
Display Board / Digital Section
Microcontroller Section
The microcontroller section consists of microcontroller U103 and the
liquid crystal display (LCD). The microcontroller has an on-board LCD
driver. R104, R116, and R118 supply the microcontroller with LCD drive
voltage for a four-plex drive. The LCD is a transmissive type that uses a
backlight for optimum readability. J104 supplies current, limited through
5 Ω(paralleled R119 and R120), +5V for the LCD diffused backlight LED
array.
The LCD indicates frequency in MHz, a user-programmable name
up to 8 characters long, and the UHF frequency group, channel, and
television channel.
The LCD also has a battery fuel gauge that indicates the state of
the transmitter battery. A padlock icon on indicates whether the user-
accessible menus are locked or unlocked. A 4.000 MHz oscillator (Y101)
provides the operating frequency to the microcontroller.
The oscillator circuit includes C107, C108, R111, R112, and Y101.
R105 and C103 form the reset circuit. R121 is the pull-up resistor for the
U103 programming voltage pin.
Memory Section The memory consists of non-volatile ferroelectric RAM or EEPROM
U106, which stores current receiver settings and maps of compatible
groups and channels. R108 and R109 allow in-circuit programming of
U106 FRAM.
Analog to Digital Converter Section
The analog to digital converter section consists of A/D converter
U101. Signal DLOW_BATT (P102.2, U101.2, I138) from the audio sec-
tion is an analog signal representing the transmitter’s battery level. This
is converted to an 8-bit digital signal for the microcontroller and is dis-
played on the LCD as the battery fuel gauge. Microcontroller U103
communicates serially with A/D converter U101.
Shure U4D Dual Diversity UHF Receiver
6
25D1062 (AG) Circuit Description
User Interface Section
The user interface section consists of switches SW101 MENU,
SW103 SELECT, SW102 UP (+), and SW104 DOWN (–). These
switches provide access to various user-programmable menus on the
front panel display. The LCD provides the user with feedback for all
switch actions performed.
Audio Output Level Control R110
The audio output level control potentiometer has no associated
circuitry in this section. Refer to the Audio Section.
RSSI Bar Graph Section
Channel A
Bar graph driver U104 gets the DRSSI_CH_A analog signal (U104.5,
P102.6, I155) from the rf-audio board and indicates its strength on the
5-LED bar graph formed by D117, D115, D110, D109, and D105.
Channel B
Bar graph driver U102 gets the DRSSI_CH_B analog signal (U102.5,
P102.11, I170) from the rf-audio board and indicates its strength on the
5-LED bar graph formed by D116, D114, D111, D108, and D106.
Audiometer Bar Graph Section
Bar graph driver U105 gets the DAUDMTR audio metering (averag-
ing only, no peak) signal (U105.5, P102.13, I156) from the rf-audio board
and indicates its strength on the 7-LED bar graph formed by D119, D118,
D113, D112, D107, D104, and D103.
Diversity LEDs D101 and D102
Diversity LEDs A and B have no associated circuitry in this section.
Refer to the Audio Section.
Digital to Analog Converter Section
The microcontroller communicates with 8-bit serial D/A converter
U215 over two signal wires, DSQUELCH (P102.3, U103.10, TP113) and
DSCL (P102.15, U103.9, T114), to set up the audio squelch threshold.
Shure U4D Dual Diversity UHF Receiver
7 25D1062 (AG)Circuit Description
Display Board Interconnect with Rf-Audio Board
Integrated ribbon cable connector P102 interfaces with the rf-audio
board and the networking Interface board through the display board. Pin
assignments for the P102 connector are presented in the table below.
Table 1
P102 Interconnect Pin Assignments
PIN NO. SIGNAL NAME DESCRIPTION
1 D+5V +5V power supply to the Digital Board
2 DLOW_BATT Analog voltage representing TX battery level
3 DSQUELCH Data signal to U215 squelch D/A
4 GND Input power ground to the Digital Board
5 DLE Data Load Enable to U309 PLL Synthesizer
6 DRSSI_CH_A Chan. A rf Received Signal Strength Indicator
7 DD Data signal to U309 PLL Synthesizer
8 DLEDA Diversity LED A drive signal input
9 DCK Clock signal to U309 PLL Synthesizer
10 DLEDRET Diversity LED A and B common return
11 DRSSI_CH_B Chan. B rf Received Signal Strength Indicator
12 DLEdB Diversity LED B drive signal input
13 DAUDMTR Audio metering analog signal input
14 N141 Audio potentiometer return to the Audio Board
15 DSCL Clock signal to U215 squelch D/A
16 N142 Audio potentiometer wiper to the Audio Board
17 DLONE_W_OUT Interrupt output to the Networking Interface
18 N143 Audio potentiometer input from the Audio Board
19 DSDO Networking Serial Data Output
20 DLONE_W_INT Interrupt input from the Networking Interface
Shure U4D Dual Diversity UHF Receiver
8
25D1062 (AG) Notes
Notes
This page intentionally left blank.
Shure U4D Dual Diversity UHF Receiver
9 25D1062 (AG)Preliminary Tests
Preliminary Tests
Test Component Locations
Rf-Audio Board, Side 1
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