Shure uc2, uc58 User Manual

Shure Incorporated

222 Hartrey Avenue

Evanston IL 60202-3696 U.S.A.

UC UHF Wireless System

SERVICE MANUAL CHANGE NOTICE

UC2 UHF HAND-HELD TRANSMITTER

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.

CHANGES EFFECTIVE [DATE]

	REMOVE					INSERT
	these pages from				the following revised pages
	your current manual				attached to this notice
	Revision 1	ALL				Revision 2 ALL
	Revision 2 pages:14,15,17,20,22,27,29 and 30			Revision3 pages:14,15,17,20,22,27,29 and 30
	SERVICE MANUAL REVISION HISTORY
	Release		Part Number			Date Code
	Original		25A1044			RI
	Revision 1		25B1044			SB
	Revision 2		25C1044			TB
	Revision 3		25C1044			TK

E1999, Shure Incorporated

Printed in U.S.A.

Service Manual

UC2 Hand-Held UHF Transmitter

25C1044 (TK)

Characteristics

General

The Shure UC2 Hand-Held UHF Transmitter is a microprocessorcontrolled microphone transmitter, operating in the 692 to 716 MHz and 774 to 862 MHz frequency range. The UC2 hand-held transmitter is used in mid-level installed sound, rental, and concert sound applications. Six frequency range variations are available.

Controls and Connectors

1

2

3

8

4

5

7

			6
1.	Mic Cartridge Grille (87 shown)	5.	9 V Battery
2.	Battery Fuel Gauge LEDs	6.	Battery Cup
3.	Power ON/OFF Switch	7.	Group Selection Rotary Switch
4.	Audio Gain Control	8.	Channel Selection Rotary Switch

Figure 1. UC2 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 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.

1999, Shure Incorporated

Printed in U.S.A.

25C1044 (TK)

Shure UC2 Hand-Held UHF Transmitter

Circuit Description

	LIMITER
	CONTROL INPUT
MIC		Σ	AUDIO
			OUT
	LIMITER	TONE KEY
+5V	CONTROL OUTPUT

	REG.	+5v		BATTERY	CALL ID
			TONE KEY
		32.768 kHz		MGMT.
			CIRCUIT	& FUEL
				GAUGE
FROM	ON / OFF	UNREG. PWR.
BATT.	SWITCH		TONE CONTROL
		PWR. OFF DETECT			4 MHz
		PLL CONTROL	MCU		EEPROM
	FET				(MEM)
	BYPASS		MC68HC705
	PWR.

CONTROL	HOLD	4 MHz
	CIRCUIT
		SYNTH.
		MB15A02
		GROUP	CHANNEL
		RF POWER	RF MUTE
		RF MUTE
	AUDIO IN
		VCO

Figure 2. UC2 Hand-Held Transmitter Circuit Block Diagram

Audio Section

FCC-Approved

Audio enters L200, an inductor used as an rf choke. The signal is ac coupled through capacitor C200 into a user adjustable gain stage. Resistors R202 and R203 set up a half-supply bias, and R204 sets the input impedance for the stage.

The back-to-back diodes, D201, are used to keep the op-amp from snapping to the rail and reverse phasing when the maximum input voltage range is exceeded.

The 30 dB adjustable gain stage is built around U200A. The user externally controls the gain of this stage. C206, C207, and C208 protect

Characteristics

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25C1044 (TK)

Shure UC2 Hand-Held UHF Transmitter

the amplifier and bias circuits from rf interference. Due to its topology, this stage is unique because it is non-inverting and allows for a gain less than unity.

Audio then enters a buffer to the pre-emphasis network and the compression stage. R213, R214, and C211 set up two corners for the pre-emphasis network. The pre-emphasis boosts the high frequencies before transmission.

This network feeds an NE575 compander, U202, that utilizes an external amplifier, U201B. The compander performs a 2:1 logarithmic compression of the audio signal. The pre-emphasis network also plays a role in setting the hinge point (0 dB gain) of the compander.

From the compressor, the processed audio enters a low-pass filter, U201D, and then a summing amplifier, U201C. The tone key (and for J frequencies, the call ID signal) is added here to the processed audio signal.

Transistors Q208 and Q209, with crystal Y200, form the tone key oscillator circuit to provide a stable, continuous 32.768 kHz sine wave. Transistor Q210 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 with the transmitted signal. 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. Q211 acts as a switch for toggling the tone key MUTE/ UNMUTE; it is controlled via the microprocessor.

The tone key signal, along with the processed audio signal, is then fed to a summing amplifier, U201C. R244, at the output of the summing amplifier, helps prevent spurious oscillations from the op-amp. After passing the ac coupling capacitor, C243, the signal is fed to the rf module via the rf choke, L207.

The battery meter circuit is comprised of U205; LEDs D203, D204, D205; and various resistors. The meter works by comparing a divided down version of the battery voltage (R250, R251) to two thresholds (set by R252, R253, and R254), and lighting the appropriate LED.

A 9 Vdc battery provides power to the audio printed circuit board (pcb), via switch S200. FET Q203 provides electrical reverse battery protection by connecting the negative battery terminal to the pcb ground only when the battery is connected with the correct polarity.

The 9 Vdc then enters U203, a low dropout 5 V regulator, which gives a clean, regulated 5 V supply to run the audio circuitry. The regulator has appropriate bypass capacitors on its input and output. Q201, Q202, Q212, Q213, and their respective resistors, provide power management and timing.

25C1044 (TK)

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Circuit Description

Shure UC2 Hand-Held UHF Transmitter

ETSI-Approved

This transmitter uses the same pcb as the domestic system, but it requires a different topology and different parts.

A limiter is inserted between the pre-emphasis and the compressor to limit the occupied bandwidth.

The buffer after the gain stage, U201A, is now an inverter with pre-emphasis and 20 dB of attenuation. Previously bypassed, the expander side of the NE575 (U202) is now activated and used as a limiter. A sample of the audio is taken from the limiter output, U202, pin 6, and sent to a control circuit that detects signals above a limiting threshold. The comparator then sends a control signal to U202, pin 5, which clamps the signal.

Rf Section

Processed audio enters R320, an internal potentiometer that is adjusted for 45 kHz deviation (40 kHz for England), 100% modulation, with a 6.8 dBu 1 kHz tone at the output of the compressor. For J frequencies, R320 is adjusted for 5 kHz deviation with 1 kHz tone injected into the mic input, to give –23.47 dBu at U201, pin 7 (TPA4).

The audio is then fed to the tuning voltage pin of the voltage controlled oscillator (VCO), which modulates the carrier directly. A phase locked-loop (PLL) frequency-synthesized system eliminates the need for multiplier stages and results in a much higher degree of spectral purity.

The VCO is shielded to prevent external rf fields from affecting its operation. Regulated 5 Vdc power from the low drop-out regulator, U311, is provided to ensure frequency stability with changes in battery voltage.

The VCO is capable of tuning from 782 to 806 MHz (FCC-approved), with a 1 to 4 V tuning voltage range. At the output of the VCO, the rf signal splits into two paths. Frequency variations by country are given in a table in the Service Procedures section.

The output of the VCO is coupled by C323 to the frequency control pin of the synthesizer, U304. The synthesizer’s internal circuitry divides the rf signal down, as necessary. The synthesizer contains a quartz-con- trolled reference oscillator circuit operating from a 4.0 MHz crystal, Y302, that is adjusted by trimmer C314.

The transmitter output frequency is user-selectable in groups of compatible channels from 782 to 806 MHz for domestic groups. Frequency selection is made via microprocessor U303, which interfaces with the user by means of the Group/Channel switches, S301 and S302.

The output of the synthesizer is a series of pulses integrated by a passive loop filter (R316, C319, R317, C353, R318, C320) to produce a control voltage signal. The control voltage signal is then connected to the VCO through buffer amplifier U306B, which is used to isolate the PLL filter from the audio modulation signals.

The VCO output is also coupled to the pre-driver and rf power amplifier through a resistive network (R322, R324, R325) and a coupling capacitor, C329.

Characteristics

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25C1044 (TK)

Shure UC2 Hand-Held UHF Transmitter

The pre-driver stage, Q302, provides approximately 6 to 8 dB of gain, which makes up for the pad. R326 and R327 provide base bias for the transistor, while R328 sets its operating current.

L303 is an rf choke used to provide power to the stage, while L304, C332, C333, C357, and C2 provide filtering/matching for the stage. The collector of Q302 feeds into the power amplifier stage via coupling capacitor C338 and a pi-matching network made up of C339, L305, and C340.

The rf power amplifier, Q304, is a dual emitter BJT. This high-gain, high-frequency low-noise device can provide +18 dBm out at its 1 dB compression point. It is biased via base resistors R331 and R332. Its operating current is controlled via emitter resistor R333.

L306 acts as a choke, and C349, C350, C355, and C356 provide a good emitter bypass to ground. The amplifier output is matched to lowpass filter U1, via L307. The low-pass filter output couples to the printed circuit board (pcb) via C347 and L308.

The transmitter can deliver +17 dBm (50 mW) maximum to the antenna for domestic frequencies; JA and JB frequency transmitters can deliver +10 dBm maximum to the antenna. During transmitter power-up and frequency selection, the rf power is muted by bringing the gates of Q303/Q305 low. This provides approximately 45 dB rf attenuation until the PLL has locked.

The transmitter rf is then unmuted by bringing the gates Q303/Q305 high. During transmitter power off conditions, voltage is first removed from the VCO by bringing the base of Q301 high. Thus, the carrier signal of the transmitter is not allowed to drift off frequency during power on/off conditions.

Digital Section

The digital section contains several circuitry blocks.

Microcontroller Section

The microcontroller section consists of the U303 microcontroller. The rotary switches indicate the UHF frequency group and channel. A 4.000 MHz oscillator provides the operating frequency to the microcontroller. The oscillator circuit includes C300, C301, and Y301. U5, R306, and C305 form the reset circuit. U5 is the reset IC that resets the U303 microcontroller if the 5 Vdc normal operating voltage falls below 4.3 Vdc. C302 and C303 form the power supply bypass filter circuit.

Memory Section

The memory section consists of U302, a non-volatile, Electrically

Erasable/Programmable Read Only Memory (EEPROM) that stores the

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Circuit Description

Shure UC2 Hand-Held UHF Transmitter

mapping of the compatible groups and channels. The microcontroller serially communicates with this part via data and clock lines to read the frequency corresponding to the Group and Channel position.

The ability to write to the memory occurs during factory programming only. During normal usage, this memory is used as a look-up table only.

R335 and R305 resistors allow the clock and data lines to be driven independently of the microcontroller port pin states during in-circuit programming of the EEPROM.

Battery Management Section

The U303 microcontroller provides low battery shutdown. The shutdown threshold is 1.88 Vdc ± 10%. A voltage lower than the shutdown threshold on U303, pin 17, shuts down the transmitter. Resistors R308 and R309 divide down the battery voltage for U303; a battery voltage less than 5.65 Vdc must shut down the transmitter.

This auto shutdown disables the audio tone key mix, mutes the rf output, and powers down the rf output amplifier section. The current draw from a 9 Vdc battery in this state is 14 ± 2.0 mA, and the battery fuel gauge is not functional. Turning off the power switch completely shuts off the transmitter.

The audio circuit description section provides information for the battery fuel gauge circuit description.

Rotary Switches for Frequency Selection

A 10-position Group switch (S302) and a 16-position Channel switch (S301) select the transmitter frequency. Both rotary switches share the same U303 microcontroller port pins (3 through 6) for a multiplexed switch read operation. The individual switches are selected by U303, pins 7 and 8. Resistors R4, R300, R302, and R303 are the pull-ups for the switch position read. Diode packs D301 through D304 isolate the switches during the multiplexed read operation.

The multiplexed scheme to read switches does not allow incorporating switch change detection based on interrupts. Also, the switches cannot be constantly scanned to determine changes because the scanning frequency being in audio range is difficult to filter out.

In a steady state, the switch selector common pins are inputs to the U303, pins 7 and 8, while U303, pins 3 through 6, are outputs. In this state, pins 4, 5, and 6 are held low while pin 3 is held high. This forces logic high level on switch selector 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 U303, pins 7 and 8.

Any switch change is comprised of state toggle from odd to even, and vice versa. Only this change is detected, and it is followed by a multiplexed switch read, in which U303, pins 7 and 8, become selectively grounded outputs to read the selected switch’s state on pins 3 through 6.

A multiplexed switch read is preceded by tone key and rf mutes. This mutes the audio in the receiver to allow a quiet change to another frequency.

Characteristics

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25C1044 (TK)

Shure UC2 Hand-Held UHF Transmitter

For JA frequencies, the Group switch has 16 positions, and the Channel switch has 10 positions.

Power Switch and Mute Interface

When a transmitter is turned off, the PWRDN signal goes to logic low on U303, pin 19. This immediately disables the tone key, and the power hold circuit automatically kicks in to bypass the power switch. This is followed by 500 mS of delay, and then the rf is muted and turned off. The power hold circuit is also disabled at this point, and the transmitter shuts off.

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Circuit Description

Shure UC2 Hand-Held UHF Transmitter

Notes

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Notes

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25C1044 (TK)

Shure UC2 Hand-Held UHF Transmitter

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

1.Remove the microphone cartridge from the UC2.

2.Use a pair of needlenosed pliers to remove the circuit board retaining ring from inside the handle.

3.Push the bezel tab-snap in the handle behind the contact pcb to remove the bezel and switch actuator.

4.Slide the circuit board out by pushing on the battery connectors.

	Bezel
Switch actuator	Right side view of microphone
Handle	Tab

Contact pcb

Circuit board subassembly

Tab

Figure 3. Bezel Removal

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Disassembly

Shure UC2 Hand-Held UHF Transmitter

		Ball screen
	Retaining		Microphone
			cartridge
	ring
		Contact	(SM58 shown)	Bezel
		board
			Audio circuit
			board
			Gain control
		Rf circuit		Switch
		board		actuator
				9 Vdc alkaline
				battery

Handle

Gain control access

Battery cup

Figure 4. UC2 Hand-Held Transmitter, exploded view.

Reassembly

To reassemble the unit, reverse the disassembly steps given above:

1.Slide the circuit board back into the handle.

2.Reinstall the retaining ring, switch actuator, bezel, and the microphone cartridge.

Disassembly and Assembly

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25C1044 (TK)