Shure uc4 Service Manual
Shure Incorporated
222 Hartrey Avenue
Evanston IL 60202-3696 U.S.A.
UC UHF Wireless System
SERVICE MANUAL CHANGE NOTICE
UC4 DIVERSITY RECEIVER
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SERVICE MANUAL REVISION HISTORY
Release Part Number Date Code
Original 25A1045 RI
Revision 1 25B1045 SB
Revision 2 25C1045 TB
Revision 3 25C1045 TK
E1999, Shure Incorporated
Printed in U.S.A.
UC4 Diversity UHF Receiver
Characteristics
General
The Shure UC4 Diversity UHF Receiver is a microprocessorcontrolled single diversity receiver operating in the 692 to 716 MHz and
774 to 862 MHz frequency range. The UC4 is used in mid-level installed
sound, rental, and concert sound applications.
Controls and Connectors
R
A B
1
Service Manual
25C1045 (TK)
2
12
1. Diversity Indicators
2. Squelch Control
3. Rf Level Indicators
4. Audio Level Indicators
5. Low Transmitter Battery Indicator
6. Group Rotary Switch
7. LED Display
8. Channel Rotary Switch
9. Equalization (
Service Note: Shure recommends that all service procedures be performed by a FactoryAuthorized Service Center or that the product be returned directly to Shure Incorporated.
Licensing: Operation may require a user license. Frequency or power-output modifications may violate this product’s approvals. Contact your country’s communications authorities.
3 4
13 14 15
EQ) Adjustment Controls
Figure 1. UC4 Controls and Connectors
5
16
7
6
10. Level (Volume) Control
11. Power On/Off Switch
12. Power Input Connector
13. Balanced (
MIC/LINE Side Switch
14.
15. Unbalanced (
LOGIC OUT Connector
16.
17. Antenna Input Connectors
8
17
LOW Z) Output Connector
HIGH Z) Output Connector
10
119
E1999, Shure Incorporated Printed in U.S.A.
25C1045 (TK)
Shure UC4 Diversity Receiver
Circuit Description
The audio circuit and rf circuit description will describe only one
channel because the other channel is identical for both. The local
oscillator (LO) section is common for both channels and will be
described separately.
Audio Section
AUDIO A
AUDIO B
NOISE A
NOISE B
MARCAD
DIVERSITY
CIRCUIT
LOW BATTERY
DETECTOR
4-POLE
LP
FILTER
TONE KEY
DETECTOR
COMPANDER DE-EMPHASIS
TTL
CIRCUIT
MUTING
CIRCUIT
SQUELCH
TTL OUT
TONE
CONTROL
TO AUDIO LEVEL BAR DISPLAY
OUTPUT
STAGE
XLR OUT
1/4” OUT
Figure 2. UC4 Audio Section Block Diagram
The audio for each channel comes from the appropriate channel
detector output of the rf section. Each channel’s audio then enters its
own adjustable gain stage.
This adjustable gain stage is used to match the audio levels coming
from each rf channel, as well as to set the correct level necessary for the
compander.
From the gain stages, each channel enters an analog switch. Noise
outputs also come from each channel detector outputs. Each noise
output enters a bandpass noise filter that measures the 50 kHz noise
present in the audio signal. The noise level is proportional to the signalto-noise ratio of the channel.
Parts Designations
MARCAD diversity system, a rectified version of the noise is
In the
sent to a bank of comparators. A version of the channel noise that is 6
dB less also enters the comparators.
The noise from one channel is compared to the noise from the other
to make sure they are within 6 dB of each other. If the noise levels are
within 6 dB of each other, the comparators send a logic high signal to the
control of each channel’s analog switch, allowing the audio to pass
through.
2
25C1045 (TK)
Shure UC4 Diversity Receiver
If the noise levels are not within 6 dB of each other, the channel with
a noise voltage 6 dB greater than the other channel is not allowed to
pass through the analog switch; that is, the comparator puts a logic
low signal on the control line for the analog switch.
Each channel’s noise is also compared to an adjustable squelch
level; a dc level. If either noise voltage is greater than the squelch
threshold, it is shut off.
The outputs from the analog switches are connected together at the
audio combining stage, 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 is a crystal filter in which the
level of tone key is converted to dc and compared against a fixed dc voltage.
The second path enters a low Q bandpass filter centered around 32
kHz. This filter is for low battery detection in the receiver. The lower Q
allows for small frequency variation of tone key from various transmitters,
without the large amplitude variations that the crystal filter would have.
The filtered signal is then rectified and averaged. The dc that is obtained
from this is amplified, triggering a comparator for the low battery LED
display.
The third path is into the compander via a 24 kHz low-pass filter with
a 32 kHz notch. The audio is expanded and de-emphasized here. The
compander output then goes off the board to a high and low frequency
equalization circuit.
A user-adjustable gain stage follows. The signal is then brought
back to the main audio board, where it enters a balanced and unbalanced output stage. The balanced output can be set for either mic or
line level, where the mic level is 30 dB down from the line level.
For the audio level meter, audio is tapped off from the 24 kHz filter’s
output and goes through a full wave precision rectifier and averaging circuit. This dc signal then enters a dc amplifier stage used to adjust levels
for the LEDs.
The output from this stage drives the audio level meter on the front
panel board. For the rf level meters, a dc voltage from the detector chip
for the received signal strength indicator (RSSI) drives the bargraph IC
on the front board.
Parts Designations325C1045 (TK)
Shure UC4 Diversity Receiver
Rf Section
DIELECTRIC
FILTER
LNA
DIELECTRIC
FILTER
FIRST
MIXER
RF CHANNEL A
FIRST IF
FILTER
SECOND
MIXER
SECOND IF
FILTER
FM
DETECTOR
AUDIO A
NOISE A
RSSI A
FROM
MICROPROCESSOR
DIELECTRIC
FILTER
FIRST LO
SYNTHESIZER
LNA
SECOND LO
VCO
DIELECTRIC
FILTER
LOW PASS
FILTER
FIRST
MIXER
FIRST IF
FILTER
RF CHANNEL B
SECOND
MIXER
SECOND IF
FILTER
FM
DETECTOR
AUDIO B
NOISE B
RSSI B
Figure 3. UC4 Rf Section Block Diagram
The rf input signal is provided from the antenna ports to the receiver
by BNC connectors. Antenna port A is connected to J101 (channel A),
and antenna port B is connected to J201 (channel B).
The rf circuit description will describe only one channel because the
other rf channel is identical. The local oscillator (LO) section is common
for both channels and will be described separately.
Rf Channel
The rf signal is pre-selected to the 782 – 806 MHz frequency range
with two dielectric filters. The first dielectric filter is located between the
antenna port and the low noise amplifier (
located between the
LNA block and mixer input.
LNA). The second filter is
Parts Designations
The
LNA and the first mixer consist of a dual gate GaAs MOSFET.
The first conversion gives the first intermediate frequency (IF) signal at
50 MHz.
The first IF signal is amplified with
MMIC, band limited with a SAW
filter, and then down-converted to the second intermediate frequency (IF)
at 10.7 MHz with a second down-converter.
The second
IF signal is filtered by 10.7 MHz ceramic filters and
amplified by a 10.7 MHz pre-amp (Q105).
The 10.7 MHz signal goes to the second IF gain block with a
detector. The audio output is buffered and then processed as stated in
the audio section circuit description. The noise output is amplified to provide signal for the noise squelch circuitry. The Received Signal Strength
Indication (RSSI) output of the detector drives the LEDs that are located
on the receiver’s front panel.
4
25C1045 (TK)
Local Oscillator (LO)
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), a loop filter, a VCO, an rf power divider, and a bandpass
filter. The PLL limits the LO signal before injection to the first down converter, Q102 and Q202.
The prescaler receives the rf signal from the VCO via the coupling
capacitor, C333. The output from the phase detector is connected to an
external loop filter that controls the tuning voltage input to the VCO. The
prescaler/synthesizer IC is a serial-programmable input IC. It receives
the frequency programming data from the microprocessor, which is set
by the user, as described in the digital circuit description.
Digital and Display Section
Shure UC4 Diversity Receiver
ROTARY
SWITCH
ROTARY
SWITCH
(FREQ)
AUDIO
RSSI A
RSSI B
(CH)
EEPROM
MICROPROCESSOR
LED DRIVER
LED DRIVER
LED DRIVER
SHIFT
REGISTER
TO SYNTHESIZER
7 LED BAR
5 LED BAR
5 LED BAR
SHIFT
REGISTER
Figure 4. UC4 Digital and Display Section Block Diagram
Parts Designations525C1045 (TK)
Shure UC4 Diversity Receiver
Microcontroller
The microcontroller section consists of a U703 microcontroller and a
two digit, seven segment, LED display.
The LED display indicates frequency in terms of compatible channels
in a group. The LED display on the left indicates the current group. The
LED display on the right indicates the channel. Each LED is capable of
displaying digits 0 – 9. However, the channel LED also displays alpha
letters A – F.
Serial shift registers, U705 and U705, latch the current LED display.
A serial Load Enable (LE) signal of the display driver section is also
shared with the rf interface section.
A 4.0 MHz oscillator, Y701, provides the operating frequency to the
microcontroller. The oscillator circuit includes capacitors C702, C703,
with the crystal oscillator, Y701.
Resistor R704, C704, and U702 make up the reset circuit. The
microcontroller is reset if the supply voltage to it drops below 4.3 Vdc.
Memory
The memory section consists of U701, a non-volatile Electrically
Erasable and Programmable Read Only Memory (EEPROM). The
EEPROM stores the mapping of the compatible groups and channels
with respect to rotary switch positions.
The microcontroller serially communicates with the memory via data
and clock lines to read the frequency corresponding to the group and
channel position. Write to the memory only occurs during factory programming. During normal usage, this memory is used as a look-up table
only.
Resistors R702 and R703 allow in-circuit programming of the U701
EEPROM by letting data and clock lines be driven independently of the
microcontroller port pin states. R701 is the pull-up resistor for the data
line.
Audio / Rf Interface
The OUT ENAB signal gives the microcontroller the ability to mute
the audio during turn on and off, and frequency changes.
The microcontroller sets the phase-lock loop (PLL) to the required
signal using the DATA signal (U703, pin 12) to send the frequency initiali-
zation and set-up data. This data is clocked into the PLL by the microcontroller through the
Enable (
into a PLL’s internal registers to initialize and set the frequency.
LE) signal (U703, pin 10). The LE signal loads the clocked data
CLOCK signal (U703, pin 12) and the Load
Parts Designations
6
25C1045 (TK)
Shure UC4 Diversity Receiver
Rotary Switches for Frequency Selection
A 10-position group switch (S701) and a 16-position channel switch
(S702) select the receiver frequency. The current position of these
switches is displayed on the 7-segment LED display. Both rotary
switches share the same U703 microcontroller port pins (3 through 6)
for a multiplexed switch read operation.
The individual switches are selected by pins 7 and 8 of the U703
microcontroller. Resistors R705 through R708 are the pull-ups for switch
position read. Dual diodes D701 through D704 isolate the switches during multiplexed read operation.
The multiplexed scheme to read switches does not allow switch
change detection based on interrupts. Also, the switches cannot be
constantly scanned to determine changes because the scanning frequency is in audio range, which makes it hard to filter out.
In a steady state, the switch common pins are inputs to pins 7 and 8
of the U703 microcontroller, while pins 3 through 6 of the microcontroller
are outputs In this state, pins 4, 5, and 6 are held low which pin 3 is held
high. This forces the logic high level on switch common pins if the
switches are set on odd positions. For even position settings, the contact
on pin 1 is open from the switch common pin, and the internal pull-down
resistors force logic low to the U703 microcontroller, pins 7 and 8.
Any switch change is done by state toggle from odd to even, or vice
versa. Only this change is detected and followed by a multiplexed switch
read. In this case, U703 microcontroller pins 7 and 8 selectively become
grounded outputs to read the selected switch’s state on pins 3 through 6.
A multiplexed switch read is preceded by an audio mute. The
receiver audio is muted to allow a quiet change to another frequency.
Power Switch Interface
When a receiver is switched off, the MT signal goes to logic low on
U703, pin 19. This interrupts the microcontroller to immediately mute the
audio so that the receiver turns off without any audio pop.
Parts Designations725C1045 (TK)
Shure UC4 Diversity Receiver
Notes
Parts Designations
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8
25C1045 (TK)
Shure UC4 Diversity Receiver
Functional Test
Verify operation and reported malfunction, referring to the product
User’s Guide for a description of the unit as well as information on its
operation, troubleshooting, and technical data.
Disassembly and Assembly
! CAUTION !
Observe precautions when handling this static-sensitive device.
Disassembly
Top Cover Removal
1. Remove two screws and washers each from the top, left, and
right sides of the receiver (6 screws).
2. Slide the top cover off of the receiver to expose the circuit
boards.
Front Panel Removal
1. Pull up on the top two tabs to partially release the front panel
from the chassis.
2. With a thin tool and the unit upside down, pry the front panel
away from the chassis at the two slots located on the bottom
of the front panel.
3. With the front panel disengaged from the chassis, carefully pull
the front panel away from the chassis.
Printed Circuit Board Removal
1. Pull the power knob off the power switch.
2. Disengage the front four standoffs from the chassis by pinching
the standoff ends, which will free the front circuit board.
3. Except for the dc power receptacle, remove all screws, nuts, and
washers from the back of the unit.
4. Unplug the connector between the dc power receptacle and the
circuit board.
5. Remove the remaining five screws that secure the circuit board.
6. Raise the front of the circuit board to clear the chassis; then
move the circuit board forward to free the rear components and
lift the circuit board out.
Parts Designations925C1045 (TK)
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