Shure slx2 User Manual

SLX2 Wireless Transmitter Service Manual

25A1090

SLX2 WIRELESS HANDHELD TRANSMITTER

PRODUCT DESCRIPTION

The Shure Model SLX2 is a µP (microprocessor) controlled frequency agile UHF handheld transmitter operating over the frequency range of 518 to 865 MHz (in eight different 24 MHz-wide frequency bands). The transmitter will operate for a minimum of 8 hours using two "AA" alkaline batteries. The User Interface includes "mode" and "set" buttons, and an LCD that displays battery status, group/channel, and transmitter/ receiver frequency synchronization. The SLX2 has a plastic enclosure, and utilizes an internal antenna for optimum range and reliability. This product is intended for use in entry-level presentation, installed, and performance markets.

SLX

mute select

FEATURES

1.Frequency agile; microprocessor controlled. Model number extension determines frequency band of operation.

2.Minimum of 12 compatible systems per SKU in the U.S. Additionally, a minimum of 12 compatible systems in the top 50 U.S. markets across all three domestic SKU's (H5, J3, and L4).

3.Operating frequency programmable locally or from the receiver using a built-in IR link.

4.Designed for use with "AA" alkaline batteries (2 required). May also be used with rechargeable "AA" batteries. Note: battery condition indicator is calibrated for alkaline batteries and may not be accurate with rechargeable types. Electrical reverse battery protection is included.

5.Minimum battery life of 8 hours with new "AA" alkaline batteries.

6.Designed for use with SM58, BETA 58, SM86, and BETA 87A&C microphone heads. Compatible with "active load" or standard heads (active load circuitry to be incorporated in heads).

7.Tone key squelch.

8.Power/Mute and Select buttons with LCD display for frequency group/channel selection and control. LED backlight for easy reading of LCD display.

9.Bicolor, green/red LED for power "on" and low battery, mute and infrared link indications.

10.Rugged plastic construction.

11.Utilizes Shure Patented ARC (Audio Reference Companding) audio processing.

©2006, Shure Incorporated 25A1090 (Rev.3)

DETAILED DESCRIPTION

1

2

SLX

3

4

mute

select

5

Features

1Interchangeable microphone head (SM58 pictured)

2Power / Infrared (IR) / Mute indicator

Green: ready Amber: mute on

Flashing red: IR transmission in process Glowing red: battery power low

Pulsing red: battery dead (transmitter cannot be turned off until batteries are changed)

3LCD screen

4On-off / mute switch

Press and hold to turn on or off. Press and release to mute or unmute.

5Select switch

6IR port

Receives infrared beam to synchronize frequencies. When using multiple systems, only one transmitter IR port should be exposed at a time.

6

SLX

mute select

Adjusting Gain

Access the gain adjustment switch a by unscrewing the head of the microphone.

Two gain settings are available on the SLX2. Choose a setting appropriate for vocal volume and for the performing environment. Use the tip of a pen or a small screwdriver to move the switch.

•0dB: For quiet to normal vocal performance.

•–10dB: For loud vocal performance.

	BIAS
AUDIO
0dB	-10dB

a

b

SLX

mute select

25A1090 (Rev.3)	2

a Incompatible

MASTER LIST

GROUP CHANNEL

i8 i8

select

b Incompatible

MASTER LIST

GROUP CHANNEL

i8 i8

select

SLX2 Transmitter Programming

Manually Select a Group and/or Channel

select

5

1.Press and hold the select button until the GROUP and CHANNEL displays begin to alternate.

2.To change the group setting, release the select button while GROUP is displayed a. While GROUP is flashing, pressing select increases the group setting by one.

3.To change the channel setting, release the select button while CHANNEL is displayed b. While CHANNEL is flashing, pressing select increases the channel setting by one.

Incompatible

MASTER LIST

GROUP CHANNEL

i8 i8

Incompatible

MASTER LIST

GROUP CHANNEL

i8 i8

Lock or Unlock Transmitter Settings

select

+

Press the mute/ and select buttons simultaneously to lock or unlock the transmitter settings. When locked, the current settings cannot be changed manually. Locking the transmitter does not disable infrared synchronization.

Battery Status

Indicates charge remaining in transmitter batteries.

Incompatible

MASTER LIST

GROUP CHANNEL

i8 i8

Incompatible

MASTER LIST

GROUP CHANNEL

i8 i8

Master List Indicator

Indicates that a master list frequency is currently in use. No group or channel information is displayed.

Note: the transmitter cannot be used to change master list settings.

INCOMPATIBLE Frequency Warning

The INCOMPATIBLE warning indicates that the receiver and transmitter are transmitting on different frequency bands. Contact your Shure retailer for assistance.

25A1090 (Rev.3)	3

AUDIO/RF BLOCK DIAGRAM

						Deviation Trim
					2-pole,	and Tone Key
		User Gain	Pre-			Sum Amp
		Control Switch		VCA	17kHz,
			emphasis		LPF
	Audio Input
	(mic head)
IR					Limiter	RMS
Photodetector
						Detector
LCD	32.768	Microcontroller Tone Key			Compressor
	kHz		Frequency
LCD			Synthesizer
Driver			control

				Audio Muting
EPROM	Channel
			RF Muting
	Select,
	Power Mute					VCO (Carrier
						Range)
	LPF	RF	Pad	RF	Pad	Loop
		Amp	0-4 dB (Band	Amp	0-4 dB (Band	Filter
			dependent)		dependent)
			+5V DC
		DC-DC	Source			Frequency
						Synthesizer
	AA Battery	Converter
	Supply
						16
						MHz

CIRCUIT DESCRIPTION

AUDIO CIRCUIT DESCRIPTION

AUDIO SECTION

Audio enters the transmitter board through pin 4 of the mic-jack board connector (CON100). Pin 2 of the connector provides 5 Vdc bias for the mic head. Pin 6 supplies the ground connection. The audio preamp (IC150-2) provides either 0 or 10 dB of gain (user switchable via SW100). Capacitor C140 couples the signal into a pre-emphasis network formed by R140, R141, and C141.

Next, the audio signal enters the patented Shure ARC™ processor. The main elements in this section are the VCA (IC100-5) and the RMS Detector (IC100-4). The VCA, or Voltage Controlled Amplifier, is a DC controlled amplifier. Following the VCA, the signal enters a 3-pole 17kHz lowpass filter stage (IC100-2) that protects the RMS detector from energy above the audio band.

Next, the signal is coupled to the RMS detector (IC100-1), which converts it to a DC voltage. A +1 dB increase at the input to the detector produces a +6 mV increase at its output. The detector output is fed to the compression threshold stage (IC150-2). This stage provides the transition from uncompressed to compressed signal. At low levels, the audio is uncompressed because diode D169 is turned off. As the AC level increases, the output of IC150-2 decreases enough to turn the diode on. As D190 conducts, the compression ratio changes from 1:1 to 5:1. Once D190 is turned fully on, the audio compression ratio remains fixed at 5:1. An additional diode in the bias

25A1090 (Rev.3)	4

network (D162) provides temperature compensation for changes in the VY, or "cut-in" voltage of D190. After the compression threshold stage, the DC control signal is amplified by a 40 dB fixedgain stage (IC100-5). It is then sent to the VCA control voltage input (EC+).

Following the ARC™ processor section, the audio signal must pass through a muting network consisting of R199, R200, C205, and Q205. A trim pot (TR200) allows the audio deviation level to be set. Next, audio enters the tone key summing amp (IC150-4). Here, tone-key is added to the audio before passing to the RF section for transmission. The tone key signal is used in the receiver to provide audio output only when the tonekey signal is present with the transmitted signal; therefore, if the tone key or the transmitter is turned off, the receiver will be muted. The tone key squelch will eliminate receiver noise associated with loss of the carrier, which usually sounds like a "pop". The tone key signal is generated by a square wave from the mP (IC300). It is then filtered by active filter stage Q185 and attenuated by R188/R189 (under µP control) before being fed to the summing amplifier. The combined audio/tone-key signal is then sent to the VCO through R504.

POWER SECTION

Two "AA" batteries supply power to the transmitter through FET Q410, which provides electrical reverse battery protection. Next, power enters switching boost converter IC400, which supplies regulated 5V power. To turn on the transmitter, SW325 shorts the base of Q480 to ground, enabling the converter and powering up the unit. The microprocessor keeps Q480 disabled until shutdown.

Power is turned off by a "shutdown" signal from the microprocessor, which can be initiated manually by the user (by holding down SW325 for 2.2 seconds) or automatically by the system (e.g., when the battery is too weak for proper operation). At this time, the microprocessor enables Q480 and shuts down the converter. When the unit is off, Q480 and its bias circuitry draw less than 30 µA, so the effect on battery life is negligible. The converter and microprocessor are disabled.

LOW BATTERY SHUT DOWN:

A software battery shutdown routine allows the battery supply to run down to 2.05 V before shutdown, and will not turn the system back on until a voltage greater than 2.25 V is present. The hysteresis keeps the system in a controlled state when the batteries are low, and also helps prevent weak batteries from being used from the start.

RF CIRCUIT DESCRIPTION

RF SECTION

The system block diagram is shown above. The SLX2 uses a PLL system with direct carrier frequency modulation. Processed audio enters the VCO through a passive "reflection" network before being applied to the varactor diode (D500) through choke L503. The VCO is shielded to prevent external RF fields from affecting its operation, and to help control radiated emissions of its harmonics. Power for the VCO and PLL circuitry is supplied by the main 5 V regulator. Power and signal lines in the VCO area are heavily decoupled and bypassed to remove noise.

The VCO has a tuning bandwidth of more than 30 MHz on all bands, with a tuning voltage range of approximately 1 to 4 volts. The VCO employs separate stages for the oscillator (Q502) and buffer (Q501) to minimize phase noise and load pulling. The VCO output is isolated by capacitive and resistive dividers, before being applied to the frequency control pin of the PLL synthesizer (IC501) through C538. The synthesizer's internal circuitry divides the RF signal down as necessary to achieve a tuning precision of 25 kHz. The synthesizer circuit contains a quartz-con- trolled reference oscillator operating from a 16 MHz reference crystal (Y801) that is adjusted by means of trimmer CV501. The transmitter output frequency is user selectable in groups of compatible channels within each of the eight available bands. Frequency selection is made via microprocessor controller IC300, which interfaces with the user by means of the Group and Channel switches, SW324 and SW325. The output of the synthesizer is a series of pulses that are integrated by a passive loop filter consisting of C532, R514, C533, R513, and C531 to produce the control voltage signal.

The VCO output is coupled to the RF buffer stage (Q600) by a matching network consisting of R602, C614, and L610. R600 and R603 provide base bias for the transistor, while R605 sets its operating current. RF choke L600 provides power and decoupling for the stage, in conjunction

25A1090 (Rev.3)	5

with C600 - C604. The collector of Q600 feeds the power amplifier stage via an impedance matching network consisting of L602, C611, and C618.

The bias voltage for the RF power amplifier (Q601) is supplied by R601 and R604. Its operating current is controlled via emitter resistor R606. RF choke L601 provides power and decoupling for the stage, in conjunction with C605-C609. For Japanese systems only, the output power is trimmed via TR640. L603, C612, and L604 provide the output impedance matching into the low pass filter, which consists of L604, L605, L606, C615, C616, and C617. The low pass filter output couples to the battery antenna via C641 and L607. Connector CON640 and C613 are only used for Japanese (JB) units. Coupling capacitor C610 is used to ensure that both batteries are driven equally.

The transmitter is capable of delivering up to +15.0 dBm to the antenna (depending on band and country). During transmitter power-up and frequency selection, the RF output is muted by bringing the base of Q631 low, which removes bias from Q630 and shuts down power to the RF stages. The RF output is also muted during the transmitter power-down sequence. This is done so that the carrier signal will not interfere with other transmissions when the loop becomes unlocked.

DIGITAL CIRCUIT DIAGRAM

Backlight

LED

RF Band					Power LED
DC Level

LCD Driver

Battery DC (Rohm LCD

Level

BU9729k)

Sythesizer

Power Mute

(National

VCO

Button

Microprocessor

Semiconducter

LMX2335)

(Motorola

MC68HC908GR16)

Select

RF Power

Button

Softstart						Tonekey
Shutdown						Squarewave

Infrared		EEPROM				Audio Mute				Tonekey
Photodetector										Level
		(MicroChip
(Sharp GP1U10X)
		93AA46 )

25A1090 (Rev.3)	6

DIGITAL SECTION

ACCESSING DIFFERENT MODES

ATE MODE

If TP_PB0 is held to TP_EGND, or logic level 0, at startup, the microcontroller will enter ATE Mode. To ensure proper operation, TP_PA0 and TP_PA1 should be held to TP_EGND at startup. In ATE Mode, each band has a three test frequencies that are controlled by the logic levels at test points TP_PA0 and TP_PA1.

				Frequency	TP_PA0		TP_PA1
				Low		0	0
				Center		0	1
				High		1	1
Test Frequencies (MHz)		H5	J3	JB	L4	P4	Q4	R5	S6
SLX2	Low	518.400	572.400	806.125	638.400	702.100	740.125	800.525	838.100
	Center	529.500	583.500	807.500	649.500	714.000	746.325	810.275	851.300
	High	541.800	595.800	809.750	661.800	725.900	751.875	819.800	864.800

RF BAND RESISTORS

Two resistors (RA and RB) are responsible to start the microcontroller in a RF band. They determine the voltage at test point TP_RFBAND.

This table shows RA's and RB's reference designators and how the voltages at the test points reflect the operating RF band.

SLX Reference Designators

	SLX2
RA		RB
R319		R320

This figure depicts the voltage divider feeding the microprocessor analog to digital converter.

.

25A1090 (Rev.3)	7

This table shows the variant resistor values and resulting voltages at TP_RFBAND for each band.

RF BAND	Rb		TP_RFBAND(+/- 0.10V)
H5		1.00k	0.30V
J3		2.99k	0.76V
L4		4.99k	1.10V
R5		7.50k	1.41V
S6		12.10k	1.81V
P4		18.2k	2.13V
Q4		30.1k	2.48V
JB		49.9k	2.75V

Note: Voltages are calculated with a 3.30V (+/- 0.10V) reference from the power supplies. If power section supports less than 3.30V, thresholds need to be adjusted.

µC DECISIONS BASED ON ANALOG VOLTAGES

	Continuous Operation Battery Thresholds
BATTERY_A2D	RF Level	Display	Logic	Voltage (V)
Measured @ 3V	- dBC		>=	2.25
block battery clips
	- dBC		<	2.25
	- dBC		<	2.14
	-8 dBC		<	2.05

Note: There is a dead battery lock voltage set at 2.30 Volts. If the transmitter is powered on with a voltage of less than 2.30 Volts, the system will lock, forcing the user to either recharge or replace the batteries. During the dead battery lock out, the battery gauge is empty and the red led flashes.

25A1090 (Rev.3)	8

NOTES

25A1090 (Rev.3)	9

FUNCTIONAL TEST

REQUIRED TEST EQUIPMENT (OR APPROVED EQUIVALENT OR SUPERIOR MODELS):

Spectrum analyzer or power meter	HP8590L/Agilent E4403B/Agilent E4407B
Digital multimeter	Fluke 87
Audio Analyzer	HP 8903B
Frequency Counter	HP 53181/HP 5385A
Power Supply	Power Supply must be able to supply 3Vdc
	with an internal ammeter.
Shielded test lead	Shure PT1838F
BNC (Male) to BNC (Male) cable (1)	Shure PT1838A
UA820 Antenna	Frequency Dependent
Audio Test Head	PT1840
Brass Ring	PT1838Y

LISTENING TEST

Before completely disassembling the transmitter, operate it to determine wether it is functioning normally and try to duplicate the reported malfunction. Refer to pages 2 and 3 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 TEST

Refer to the Disassembly section to partially disassemble the transmitter for the following functional tests.

TEST SETUP

1.Remove the PCB from the handle.

2.Set gain switch to “0” dB.

3.Connect the (+) terminal of the power supply through a milliammeter to the (+) battery terminal and the (-) power supply terminal to the (-) battery terminal.

4.Connect a DC Voltmeter across the power supply and set the power supply for 3Vdc.

5.Connect the audio analyzer to the microphone via the microphone test head (PT1840) as needed.

DISPLAY TEST

1.Power unit ON.

2.Verify that all display segments are displayed for approximately 2 seconds. This includes a full battery indication and "1818" displayed for group and channel.

REVERSE BATTERY PROTECTION TEST

1.Adjust power supply to -3.0 ± 0.1 V dc.

2.The current should be less than 0.5 mA.

VOLTAGE REGULATION TEST

With power applied properly, and the unit switched on, measure the DC voltages at the following test points. All test points are located on the top side of the PCB. Refere to the component diagram.

•TPBATT+ (Battery input) = 3 ± 0.2 Volts

•TP5V (Power Converter) = 5 ± 0.2 Volts

•TP3.3V (Power Converter) = 3.3 ± 0.2 Volts

•TPA1 (Audio Preamp) = 2.5 ± 0.2 Volts

•TPA3 (Tone Key Summing Amp (IC150 Pin 14)) = 2.5 ± 0.2 Volts

•TPVREF (IC100 Pin 5) = 2.5 ± 0.1 Volts

CURRENT CONSUMPTION TEST

1.With +3V applied to the battery terminals and the unit powered on.

2.Verify the current drain is 130 ± 15mA.

25A1090 (Rev.3)	10

FREQUENCY RESPONSE TEST

1.Set the audio generator as follows:

•Frequency = 1 kHz

•Amplitude = -20 dBu

•Filters = 30 kHz LPF

2.With the audio analyzer, probe TPA2 (top side), it should read -3.4dBu ± 0.5dB. Record this level using the Ratio button. This level will be used as your reference level for the following test.

3.Change the generator's frequency to 100Hz and measure the level at TPA2 to be -2.2dB ± 0.2dB relative to the 1kHz reference level.

4.Change the generator's frequency to 10kHz and measure the level at TPA2 to be +2.3dB ± 0.2dB relative to the 1kHz reference level.

5.Disengage the Ratio button.

DISTORTION TEST

1.Set the audio generator frequency to 1kHz with an amplitude of -20.0dBu.

2.Activate the 30kHz LPF on the audio generator.

3.Measure the total harmonic distortion and noise (THD+N) at TPA2 to be less than 0.7%.

RADIATED RF OUTPUT POWER AND FREQUENCY STABILITY TEST

1.Choose any group and channel free of interference. Using a spectrum analyzer with the appropri- ate-band UA820 antenna, measure the approximate near field radiated power as follows:

•SPAN=100 MHz

•REF LVL=10dBm

•FREQUENCY=(Look at tables on pages 18 thru 23)

2.Extend the UA820 away from the analyzer into the horizontal plane (straight out). Align the SLX2 antenna parallel to the UA820 as close as possible. Move the unit along the UA820 antenna until you find a maximum peak.

3.Do a peak search and measure the power to be at least 2 dBm for H5, J3, L4, and P4 bands and at least 0 dBm for Q4, R5, JB, and S6 bands.

4.Set SPAN to 200 KHz. Measure the frequency to be within +/- 3 kHz of the nominal frequency you are testing. (See frequency tables on pages 19 to 24).

TONE KEY LEVEL TEST

1.Set Power Supply to 3.0VDC

2.Find transmitting carrier on the spectrum analyzer with a span of 200 kHz. Use the "Peak Search, Marker Delta, Next Peak" soft-keys on the analyzer.

3.Measure the 32.768 kHz tone key level to be -21 dBc ± 1.5 dB.

4.Set Power Supply to 2.1 V (1 segment on LCD battery icon).

5.Measure the 32.768 kHz tone key level to be -14 dBc ± 1.5 dB.

OCCUPIED BANDWIDTH TEST (JB model only)

1.Set transmitter gain to maximum.

2.Set up the HP-8591E spectrum analyzer to measure Occupied Bandwidth with the following settings:

•Percentage Power = 99.5%

•Channel Spacing = 250 kHz

•Bandwidth = 110 kHz

3.Connect the audio generator to TQG connector CON90. Use a 1 kHz tone with a level that gives - 23.47 dBu (52mV) at TPA3.

4.Increase the audio level by 36dB.

5.Measure Occupied Bandwidth to be less than 110 kHz.

ADJACENT CHANNEL POWER TEST (JB model only)

1.Set the spectrum analyzer, and audio input level to the same settings as stated in “Radiated RF Output Power and Frequency Stability” and “Distortion Test”.

2.Measure Extended Adjacent Channel Power to be less than -60 dB.

IF ALL TEST PASSED, THIS MEANS THE UNIT IS PROPERLY FUNCTIONING, AND

NO ALIGNMENT IS REQUIRED.

25A1090 (Rev.3)	11