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

Changes or corrections have been made to this service manual. Update your service manual by replacing the pages listed in the table below with the ones attached to this change notice.

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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.

Service Manual

UC4 Diversity UHF Receiver

25C1045 (TK)

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

2

3

4

5

6

7

8

9

10

11

	12
	13	14	15	16		17
1.	Diversity Indicators				10.	Level (Volume) Control
2.	Squelch Control				11.	Power On/Off Switch
3.	Rf Level Indicators				12.	Power Input Connector
4.	Audio Level Indicators
					13.	Balanced (LOW Z) Output Connector
5.	Low Transmitter Battery Indicator
					14.	MIC/LINE Side Switch
6.	Group Rotary Switch
					15.	Unbalanced (HIGH Z) Output Connector
7.	LED Display
					16.	LOGIC OUT Connector
8.	Channel Rotary Switch
9.	Equalization (EQ) Adjustment Controls				17.	Antenna Input Connectors

Figure 1. UC4 Controls and Connectors

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.

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		4-POLE				TONE	OUTPUT	XLR OUT
		LP	COMPANDER		DE-EMPHASIS
AUDIO B						CONTROL	STAGE	1/4” OUT
		FILTER
					TO AUDIO LEVEL BAR DISPLAY
NOISE A	MARCAD	TONE KEY	MUTING		SQUELCH
	DIVERSITY
			CIRCUIT
NOISE B	CIRCUIT	DETECTOR
	LOW BATTERY		TTL	TTL OUT
	DETECTOR		CIRCUIT

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 signal- to-noise ratio of the channel.

In the MARCAD diversity system, a rectified version of the noise is 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.

Parts Designations

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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.

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Parts Designations

Shure UC4 Diversity Receiver

Rf Section

RF CHANNEL A

		FIRST		SECOND
		MIXER		MIXER
					FM	AUDIO A
DIELECTRIC	LNA	DIELECTRIC	FIRST IF	SECOND IF		NOISE A
FILTER		FILTER	FILTER	FILTER	DETECTOR
						RSSI A

	FIRST LO			SECOND LO
FROM			LOW PASS
MICROPROCESSOR	SYNTHESIZER	VCO
			FILTER
						AUDIO B
DIELECTRIC	LNA	DIELECTRIC	FIRST IF	SECOND IF	FM	NOISE B
FILTER		FILTER	FILTER	FILTER	DETECTOR
						RSSI B
			FIRST	SECOND
			MIXER	MIXER

RF CHANNEL 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 (LNA). The second filter is located between the LNA block and mixer input.

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.

Parts Designations

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25C1045 (TK)

Shure UC4 Diversity Receiver

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

EEPROM

	ROTARY	SHIFT	SHIFT
		REGISTER	REGISTER
	SWITCH
	(CH)
		MICROPROCESSOR
	ROTARY	TO SYNTHESIZER
	SWITCH
	(FREQ)

AUDIO	LED DRIVER	7 LED BAR
RSSI A	LED DRIVER	5 LED BAR
RSSI B	LED DRIVER	5 LED BAR

Figure 4. UC4 Digital and Display Section Block Diagram

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Parts Designations

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 initialization and set-up data. This data is clocked into the PLL by the microcontroller through the CLOCK signal (U703, pin 12) and the Load Enable (LE) signal (U703, pin 10). The LE signal loads the clocked data into a PLL’s internal registers to initialize and set the frequency.

Parts Designations

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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.

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Parts Designations

Shure UC4 Diversity Receiver

Notes

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Parts Designations

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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.

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Parts Designations