Shure U1 User manual

Shure Incorporated
222 Hartrey Avenue
Evanston IL 60202-3696 U.S.A.
UHF Wireless System
E2000, Shure Incorporated Printed in U.S.A.
25–1021–2 (BG)
SERVICE MANUAL CHANGE NOTICE
U1/U1L UHF BODY-PACK TRANSMITTER
Changes and corrections have been made to the Service Manual for the U1/U1L UHF Body-Pack Trans-
mitter. These changes will make it easier to repair the transmitters. 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.
U1/U1L SERVICE MANUAL REVISION HISTORY
Release Part Number Date Code
Original 25A1021 QE
Revision 1 25B1021 SA
Revision 2 25C1021 TD
Revision 3 25C1021 AG
Revision 4 25C1021 BF
Revision 5 25C1021 BG
CHANGES EFFECTIVE JULY 12, 2002
REMOVE
these pages from the
U1/U1L Service Manual
INSERT
these Revised pages into the
U1/U1L Service Manual
21 to 25 21 to 25

E1999, Shure Incorporated Printed in U.S.A.
25B1021 (BG)
Service Manual
U1/U1L Body-Pack
UHF Transmitter
General
Characteristics The Shure U1/U1L Body-Pack UHF Transmitter is a microprocessor-
controlled body-pack transmitter operating in the UHF frequency range.
This product is intended for use in high-end installed sound, rental, and
concert sound applications. Different frequency variations are available.
Controls and Indicators
1. Antenna
2. Programmable Display
3. Input Connector
(U1L uses LEMO connectors)
4. ON/OFF Switch
5. On/Off LED
6. Belt Clip
7. MODE Button
12 13
11
10
O
N
5
41
69
7
2
O
FF
13
8
8. SET Button
9. Audio Gain Control
10. Battery Cover Release Tabs
11. Battery Compartment Cover
12. Battery Fuel Gauge
13. Battery Compartment
NOTE: All models shipped after February 1999
have a soldered attached antenna to replace the
screw-on removable antenna. .
Figure 1. U1/UL Transmitter Controls and Indicators
Service Note: 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 U1/U1L Body-Pack UHF Transmitter
25C1021 (BG)2
Circuit Description
Circuit Description
Audio Section Audio enters L201, an inductor that is used as an rf choke. The
signal enters a 6 dB pad made up of R203, R204, C204, and C206.
The signal is ac-coupled through C205 into a 40 dB (30 dB for JB
frequencies) user-adjustable gain stage around U201A.
This gain stage is externally accessible to the user. C201, C202,
and C207 protect the pre-amplifier and bias circuits from rf interference.
R205 and R207 set up a half-supply bias, and R206 sets the ac input
impedance.
The amplified audio signal is then passed through a pre-emphasis
network before entering the compression stage. R208, R211, and C211
set up two corners for the pre-emphasis network. The pre-emphasis
network boosts the high frequencies before transmission and helps set
the hinge point (0 dB gain) of the compandor. The network feeds NE575
compandor U203, which utilizes an external amplifier U202B. The com-
pandor performs 2:1 logarithmic compression of the audio signal.
Transistors Q201 and Q202, along with crystal Y202, form the tone key
oscillator circuit, which provides a stable, continuous 32.768 kHz sine wave.
Transistor Q204 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 in the transmitted signal. Therefore, if
the tone key or the transmitter is turned off, the receiver will be muted.
Q203 acts as a switch for toggling the tone key on and off. It is controlled
via the microprocessor. R224 allows the tone key amplitude level to be set.
The tone key circuit is powered by U208B, which is a dc amplifier
that multiplies the 3 V battery voltage to 4.5 V (gain = 1.5). As the battery
voltage drops, the tone key supply voltage also drops, which decreases
oscillator amplitude. The tone key amplitude is used by the receiver
to indicate transmitter battery strength.
The tone key feature indicates battery level at the receiver. It is not
available on JB models.
The tone key signal, along with the processed audio signal, is fed to
summing amplifier U202A. Resistors R232 and R233 set up a half-supply
bias. Resistor R231, located at the output of the summing amplifier, pre-
vents spurious oscillations from the operational amplifier. After passing
through ac-coupling capacitor C232, the signal is fed to the rf module.

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3
25C1021 (BG) Circuit Description
Rf Section Processed audio enters R243, an internal potentiometer adjusted for
45 kHz deviation (100% modulation) with a –7.2 dBV, 1 kHz tone, at the
output of the front audio stage (pin 1 of U201). On JB models, R243 is
adjusted for 5 kHz deviation with –63.2 dBV, 1 kHz tone, at the input to
the transmitter.
The audio is then fed to the tuning voltage pin of the voltage controlled
oscillator (VCO) and modulates the carrier directly. The use of a phase
locked-loop (PLL) frequency synthesized system eliminates the need for
multiplier stages, resulting in a much higher degree of spectral purity. The
VCO is shielded against interference from external rf fields. Regulated
+5 Vdc power from the dc-to-dc converter ensures frequency stability,
even if the battery voltage changes.
At the output of VCO U205, the rf signal splits into two paths. The
output of the VCO is coupled by C244 to the frequency control pin of
synthesizer U204. The synthesizer’s internal circuitry divides the signal
as necessary to reach the desired reference frequency.
The synthesizer contains a quartz-controlled reference oscillator
circuit, including a 4.0 MHz crystal (Y201), that is adjusted by means of
trimmer capacitor C239.
The transmitter output frequency is user-selectable. Frequency
selection is made via microprocessor U103, which interfaces with the
user by means of the mode/select switches. The output of the synthesiz-
er is a series of pulses that are integrated by a passive loop filter (R238,
C245, R240, C266, C267, R239, and C247) to produce a control voltage
signal. The control voltage signal is then connected to the VCO through
amplifier U210A, which is used to isolate the PLL filter from the audio
modulation signals.
The VCO output is also coupled to an rf power amplifier through a
resistive pad consisting of R254, R255, R256, R257, and an LC match-
ing network containing C261, L209, and C248. The rf power amplifier,
dual gate MESFET Q208, is fixed-tuned and configured as a common
source device.
Amplifier stability is obtained through resistive loading on the input,
R247. The output of Q208 contains a low-pass matching network (L206)
and an LC-type low-pass filter (LP206), which provide a high degree of
spectral purity. The output of the low-pass filter feeds a microwave isola-
tor that reduces the production of reverse third-order intermodulation
products.
The transmitter is capable of delivering a maximum of +10 dBm
(10 mW) to the 50 Ωantenna. During transmitter power-up and frequency
selection, rf power is muted by bringing the base of Q209 high. This pro-
vides approximately 45 dB rf attenuation until the PLL has locked. The
transmitter rf is then unmuted by bringing the base of Q209 low. During
transmitter power off conditions, voltage is first removed from the VCO by
bringing the base of Q207 high. In this way, the transmitter carrier signal is
not allowed to drift off frequency during power on or power off conditions.

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25C1021 (BG)4
Circuit Description
Transmitter Display Board
The display board consists of the following circuitry blocks.
Microcontroller Section
The microcontroller section consists of microcontroller U103 and the
liquid crystal display (LCD). The microcontroller has an on-board liquid
crystal display (LCD) driver. R111, R113, and R114 supply the microcon-
troller with the LCD drive voltage for a four-plex drive. The LCD indicates
the UHF frequency group and channel. The LCD also has a battery fuel
gauge. A 4.000 MHz oscillator, Y101, provides the operating frequency to
the microcontroller. The oscillator circuit includes C107, C108, R102, and
R103, which along with Y101, U106, R112, and C112, form the reset cir-
cuit. U106 is the reset integrated circuit (IC) that resets the U103 micro-
controller if the 5 V normal operating voltage falls below 3.5 V. R107 is
the pull-up resistor for the U103 programming voltage pin.
Memory Section The memory section consists of U101, a non-volatile EEPRAM,
that stores current transmitter settings and the mapping of compatible
groups and channels.
Battery Management Section
The battery management section consists of comparator U102. It is
used to measure the effective battery voltage, with reference to +5 V, by
measuring the time used to charge a capacitor to a reference threshold
of 0.1 Vdc ±0.01 Vdc. The battery is checked approximately every 5
seconds. Comparator U102 alternately charges C106 with +5 V refer-
ence voltage, then the battery voltage (PLUS signal, test point I109).
User Interface Section
The user interface section consists of the Power, Mode, and Set
switches. The status of each switch function is indicated on the LCD.
Power Supply Section
The U105 dc-to-dc converter provides the transmitter with regulated
+5 V derived from two AA batteries. Power MOSFET Q101 provides
reverse battery protection. Q103, R118, R286, and C124 control the
soft start and reset of dc-to-dc converter following battery voltage drops.

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5
25C1021 (BG) Preliminary Tests
Preliminary Tests
Test Component Locations
MC68H
ABCD
Digital Display Board,
Side 1 Digital Display Board,
Side 2
*
*Shorted with a
0 Ωresistor on F
board versions
and later.
Rf-Audio Board,
Side 1 Rf-Audio Board,
Side 2
**
*On F
board
versions
and later.
*On F
board
versions
and later.
*
Mic-Jack Board,
LEMO 4-Pin, Mic-Jack Board, TINI Q-G 4-Pin,
Figure 2. Test Component Locations

Shure U1/U1L Body-Pack UHF Transmitter
25C1021 (BG)6
Preliminary Tests
Listening Test Before completely disassembling the transmitter, operate it to deter-
mine whether it is functioning normally and try to duplicate the reported
malfunction. Refer to the User Guide for operating instructions, trouble-
shooting, 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 Tests
Refer to the Disassembly section to partially disassemble the
transmitter for the following functional tests.
Use dc blocks at all rf outputs to protect test equipment.
Test Setup
1. Use a U4 receiver for the following functional tests.
2. Dc voltages are present at most rf test points. Use dc blocks
to protect the test equipment, if necessary.
3. Connect the (+) power supply terminal through a milliammeter
to the (+) contact on the battery nest, and the (–) power supply
terminal to (–) the contact on the battery nest.
4. Connect a dc voltmeter across the power supply and set the
power supply for +3 Vdc..
5. Connect the audio generator to the mic-jack board either via the
TINI QG connector, or the LEMO connector to BNC cable,
depending on mic style.
Rf Power
1. Attach a U4 antenna to the spectrum analyzer.
2. Turn the U1 on and hold it very close to the antenna. Move the
U1 up and down to maximize power on the spectrum analyzer.
3. Verify that output power is greater than 3 dBm.
Current Drain
1. Apply 3.0 Vdc to the battery terminals.
2. Verify that the current drain is less than 110 mA.

Shure U1/U1L Body-Pack UHF Transmitter
7
25C1021 (BG) Preliminary Tests
Frequency Response
If the U1 has an attenuator switch on the back of the unit,
it should be set to –6 dB for the following tests (versions G or later).
Values between board versions may vary slightly; the following values
are typical values.
1. With the transmitter set to minimum gain, apply 200 mVrms
at 1 kHz to its input.
2. Connect the audio analyzer’s input to the unbalanced output of
the U4 receiver.
3. Make sure the receiver volume control is set to maximum.
4. With respect to the 1 kHz level, measure –8.22 dBu ±2 dB.
5. Change the frequency to 100 Hz. Verify that the measurement
from the U4 unbalanced output is within ±2 dB with respect to
the 1 kHz level.
6. Change the frequency to 10 kHz. Verify that the measurement
from the U4 unbalanced output is within ±2 dB with respect to
the 1 kHz level.

Shure U1/U1L Body-Pack UHF Transmitter
25C1021 (BG)8
Notes
Notes
This page intentionally left blank.

Shure U1/U1L Body-Pack UHF Transmitter
9
25C1021 (BG) Disassembly and Assembly
Disassembly and Assembly
ATTENTION
Observe precautions when handling this static-sensitive device.
Disassembly
NOTE: All models shipped after February 1999 have a soldered
attached antenna to replace the screw-on removable antenna.
Do not try to remove and replace the soldered attached antennas.
1. Open the battery compartment cover and remove the batteries.
2. Remove the belt clip.
3. Remove the two screws from the back of the case.
4. Lift the top half of the transmitter case away to expose
the printed circuit boards.
5. Remove the two screws securing the battery nest to the chassis.
6. Remove the rf ground screw, located next to the antenna.
7. Lift the printed circuit boards out of the case.
BELT CLIP
BATTERY NEST
ANTENNA
RF GROUND SCREW
TOP COVER
BATTERY COMPARTMENT COVER
RF-AUDIO CIRCUIT BOARD
DIGITAL DISPLAY CIRCUIT BOARD
CONDUCTIVE WASHER
(SLIPS OVER ANTENNA)
RF SHIELDING GASKET
NOTE: All models shipped after February 1999
have a soldered attached antenna to replace the
screw-on removable antenna. .
Figure 3. U1/U1L Hand-Held Transmitter Disassembly

Shure U1/U1L Body-Pack UHF Transmitter
25C1021 (BG)10
Disassembly and Assembly
Reassembly After completing all repairs, replace the antenna. Then place the
circuit boards back in the case, making sure the multi-pin connectors on
the boards mate. Reassemble the transmitter by performing the steps of
the disassembly procedure in reverse order.

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11
25C1021 (BG) Service Procedures
Service Procedures
Service Notes
Units With Date Codes
Earlier Than August 1996
A small number of synthesizer ICs (U204) can experience start-up
problems with the 4 MHz crystal reference oscillator. The problem will
only occur for certain values of tuning capacitance.
The transmitter displays the correct group and channel information.
However, the carrier will have moved to its lowest possible frequency
(around 750 MHz). The tuning voltage of the VCO will read 0 Vdc.
Adjusting the crystal’s tuning capacitor to its lowest value should
cause the 4 MHz crystal oscillator to start up, and the carrier will lock
to the proper frequency.
The tuning capacitor can now be readjusted to center the carrier to
within ±1000 kHz. However, once the unit is turned off, the problem may
return.
All units with August 1996 date codes or later have a 10 kΩresistor
from pin 2 of the synthesizer to ground to insure that the internal
oscillator will start up for all values of tuning capacitance (C239). Safe
values for the resistor are from 16.8 to 33.2 kΩ.
Product Changes
Antenna Changes
All models shipped after February 1999 have a soldered attached
antenna (70A8017) to replace screw-on removable antenna.
Attenuator Switch SW201
Attenuator switch SW201 has been added to the audio section of the
rf-audio printed circuit board. All products shipped after February 1997
(board versions “F”and later) should include this switch.
Inductor L104 Removal
Inductor L104 has been removed for improved electrostatic
discharge (ESD) performance. On products shipped after March 1997,
L104 was replaced with a jumper.
On “F”and later versions of the board, the circuit was redesigned
and the jumper was removed. Shure recommends that any product
shipped before March 1997 have L104 removed and replaced with a
jumper.
Comparator U102
Comparator U102 has been changed to prevent an “88 88”display.

Shure U1/U1L Body-Pack UHF Transmitter
25C1021 (BG)12
Service Procedures
Antenna Replacement
NOTE: All models shipped after February 1999 have
a soldered attached antenna to replace the screw-on
removable antenna. Do not try to remove and replace
the soldered attached antennas.
The top printed circuit board (pcb) is connected to the bottom pcb by
a multi-pin connector. Two wires also lead to the battery connector and a
three-wire flat cable that connects the pcbs to the microphone jack.
Handle the pcbs with care to avoid damaging these connections.
1. Open the battery compartment cover and remove the batteries.
2. Remove the belt clip.
3. Remove the two screws from the back of the case.
4. Lift the top half of the transmitter case away to expose the pcbs.
5. Remove the single screw visible next to the antenna connector.
6. Use the antenna to gently lift up both pcbs far enough so that the
antenna assembly clears the case, or remove the top pcb to gain
better access to the bottom pcb.
7. Remove the antenna by unscrewing it from the connector.
Make sure that the washer on the antenna clears the case.
8. Install the new antenna by screwing it onto the connector. If
necessary, replace the conductive rubber gasket at the base
of the antenna.
9. Return the pcbs to their original position.
10. Reinstall the single screw next to the antenna connector.
11. Perform these steps in reverse order to reassemble the unit.

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13
25C1021 (BG) Service Procedures
Measurement Reference
dBu is a measure of voltage, and dBm is a measure of power.
For example, the HP8903 should be labeled dBu instead of dBm
because it is a voltage measurement. These two terms are often used
interchangeably even though they have different meanings.
Audio levels in dBu are marked as dBm on the HP8903.
dB Conversion Chart
0 dBV =2.2 dBu
0 dBu =0 dBm, assuming the load = 600 Ω
Test Equipment Most test equipment needed is described in the Shure Wireless
Service Equipment Manual. The following test equipment (or approved
equivalent) is also needed. Table 1
Test Equipment
Equipment Type Model
Audio analyzer *Hewlett-Packard 8903B
Digital multimeter Fluke 87
Interconnect Cable Shure PT1843
BNC (Male) Cables (2) Shure PT1838A
DC Blocker Shure PT1838W
BNC (Female) to 1/4-inch Phone Plug Adapter Shure PT1838C
20 dB Attenuator Shure PT1838T
BNC to QG Cable Shure PT1825
BNC to LEMO Cable Shure PT1878
BNC (Female) to SMC (Female) Adapter Shure PT1838S
BNC (Female) to SMC (Female) Adapter Shure PT1838S
Test Cable, Japan Version Shure PT1838–AF
Adapter, Japan Version Shure PT1838–AJ
BNC (Male) to RG–174 Cable, unterminated Shure PT1824
Frequency counter Hewlett-Packard 53181A
Rf signal generator Hewlett-Packard 8656B
Spectrum analyzer Hewlett-Packard 8590L
Shure U4S receiver Shure U4S
*Audio levels in dBu are marked as dBm on the HP8903B.
Printed Circuit Board Interconnecting Cable
This cable is provided with the standard test equipment and is used
to connect U1 circuit boards that have been removed from the case for
servicing. It is made from two custom Shure printed circuit boards, a four-
inch, 11-wire ribbon cable, and one male (Shure 170A07) and one
female (Shure 170A08) surface-mount connector. Note that the SMC
connectors face in opposite directions.
Female SMC connector Male SMC connector
(on back side)
Figure 4. Printed Circuit Board Interconnecting Cable

Shure U1/U1L Body-Pack UHF Transmitter
25C1021 (BG)14
Service Procedures
Rf Alignment
CH 2
FREQUENCY COUNTER
CH 1
J3
U1 Transmitter Frequency Counter
Power (S103): ON Connect CH2: J3
Gain (R201): For JB models:
set to maximum
Figure 5. Alignment Test Set–Up
Rf Alignment Set-Up
1. Proper adaptors should be used to connect the test equipment.
2. Use RG58 or other low-loss 50 Ωcables for all rf connections.
3. Include the insertion loss of the cables and connectors in
rf conductive power measurements.
4. Connect the rf–audio board to the digital board through
board interconnects J104 and J200.
5. On all models except JB, audio GAIN potentiometer R201 does
not need to be preset to any position. On JB models, R201
GAIN should be set to maximum.
6. All rf measurements should be made from the antenna output
connection, the 50ΩSMC connector on PCB versions “G”and
earlier or through the P1824 test cable on PCB versions “H”and
later. For JB models with SMT rf test connector, use PT1838–AF
with PT1838–AJ.
Rf Alignment
1. Slide the ON/OFF switch (S103) to the ON position.
2. Connect the transmitter to the frequency counter via J3.
3. Determine the transmitter operating frequency by comparing the
Group and Channel information on the LCD to the tables in the
User Guide and User’s Guide Supplements.
4. Adjust variable capacitor C239 until the frequency counter mea-
surement matches the desired operating frequency, ±1 kHz.

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15
25C1021 (BG) Service Procedures
Power Output Measurement
The output power measurement ensures that the output signal is
strong enough for sufficient range when the system is in use. The output
power measurement also verifies that the output power is not above the
specified maximum level, to ensure compliance with regulatory agencies’
standards.
SPECTRUM ANALYZER
U1 Transmitter Spectrum Analyzer
Power: ON Peak search: ON
Signal track: ON
Marker: ON
Figure 6. U1 Power Output Measurement Test Set-Up
1. Rf output power is not adjustable. Use RG58 or any other low
loss 50 Ωcables for all rf connections.
2. Include the insertion loss of the cables and connectors in
rf conductive power measurements.
3. Using the spectrum analyzer, verify output power is at least
+8 dBm. JB models must be at least +8 dBm and cannot exceed
+10 dBm.

Shure U1/U1L Body-Pack UHF Transmitter
25C1021 (BG)16
Service Procedures
Audio Alignment
Deviation Reference Voltage
RF SIGNAL GENERATOR AUDIO ANALYZER
S201
TONE-KEY
SWITCH U4 RECEIVER
NOTE: DC VOLTAGES ARE PRESENT
AT MOST RF TEST POINTS. USE A
DC BLOCK ON THE RF SIGNAL
GENERATOR TO PROTECT
TEST EQUIPMENT.
DC BLOCK
U4 Receiver Audio Analyzer Rf Signal Generator
Output: Unbalanced Measurement: AC level INT: FM
Gain: Maximum Filters: INT: 1 kHz
Squelch: Mid Low-Pass (30 kHz): ON Output Amplitude: –50 dBm
Tone Key (S201): OFF High-Pass (400 Hz): ON
Figure 7. Deviation Reference Voltage Test Set-Up, Using a U4 Receiver
1. The U1 transmitter should be turned OFF for this procedure.
2. Connect the rf signal generator to antenna A or B on a U4
receiver. Make sure the dc block is on the rf signal generator.
3. Set the rf signal generator to the same frequency as the
U1 transmitter.
4. Set rf signal generator modulation to 1 kHz and set the deviation
to 45 kHz for UA, UB, MA, MB, MC, and MD models, 40 kHz for
KK models, and 5 kHz for II models.
5. Set the output amplitude of the rf signal generator to –50 dBm.
6. Turn the U4 receiver ON and set the tone key switch (S201)
inside the U4 receiver to the OFF position. This will disable the
receiver tone key function.
7. Connect the audio analyzer to the unbalanced output of the U4
receiver. The voltage should be 4.2 ±0.5 dBu (1.26 ±0.07 V) for
UA, MA, MB, MC, MD, and KK models, and –26.2 ±0.5 dBu for
II models.
Note the voltage obtained; it is the deviation reference voltage.
8. Disconnect the rf signal generator from the U4 receiver and
return the tone key switch (S201) to the ON position.

Shure U1/U1L Body-Pack UHF Transmitter
17
25C1021 (BG) Service Procedures
Deviation Reference Voltage Adjustment
AUDIO ANALYZER
U4 RECEIVER
20 dB PAD
DC BLOCK
NOTE: DC VOLTAGES ARE PRESENT
AT MOST RF TEST POINTS. USE A
DC BLOCK ON THE RF SIGNAL
GENERATOR TO PROTECT
TEST EQUIPMENT.
U1 Transmitter Audio Analyzer
Power: +3 Vdc Measurement: AC level
Gain: Minimum; for JB models,
set to MAX Output: 1 kHz
Filters:
Low-Pass (30 kHz): ON
High-Pass (400 Hz): ON
Figure 8. Deviation Reference Voltage Adjustment Test Set-Up
1. The U1 transmitter should be turned ON for this procedure.
2. Turn the rf signal generator OFF for this procedure.
3. For G and later board versions, adjust the audio analyzer for 1
kHz to get a level of –5.0 dBu (436 mV) at pin 7 of U201.
4. For F or earlier board versions, adjust the audio analyzer for
1 kHz to get a level of –5.0 dBu (436 mV) at pin 1 of U201.
5. On JB models, adjust the audio analyzer for 1 kHz to –61.0 dBu
at the input connector.
6. Connect the transmitter rf output to a U4 antenna connector
through a dc block and a 20 dB pad.
7. Connect the U4 unbalanced output to the audio analyzer’s input.
8. Adjust R243 until the audio analyzer reads the deviation
reference voltage, measured in the last test, from the
unbalanced output of the U4 receiver, ±0.1 dB.
9. Turn OFF the 30 kHz low-pass filter and the 400 Hz high-pass
filter on the audio analyzer.
10. Disconnect the audio analyzer output from the U1 mic input.

Shure U1/U1L Body-Pack UHF Transmitter
25C1021 (BG)18
Service Procedures
Tone Key Level Adjustment
AUDIO ANALYZER
U1 Transmitter Audio Analyzer
Power: +2.5 Vdc Measurement: AC level
Gain: Minimum; for JB models,
set to MAX Output: None
Filters:
Low-Pass (30 kHz): OFF
High-Pass (400 Hz): OFF
Figure 9. Tone Key Level Adjustment Test Set-Up
1. Use a dc power supply to apply 2.5 ±0.01 V to the battery
terminals, with no audio applied to the audio input.
2. Make sure no filters are used on the measuring instrument.
3. The tone key frequency will be approximately 32.768 kHz.
Adjust R224 so that the tone key level of –22.8 ±0.1 dBu
(56 mV) is measured at U202, pin 1. For JB models, this level
should be –24.7 dBu ±0.1 dBu (45 mV).