Ericsson LBI-38505A User Manual

LBI-38505A

(Supercedes LBI-30025)

Maintenance Manual

®

MASTR

BASE STATION
406-512 MHz RECEIVER

II

ericssonz

TABLE OF CONTENTS

RF ASSEMBLY, MIXE R AND

REFILTER BOARD . . . . . . . . . . . . . LBI-30032

(DF1107)
OSCILLATOR/MULTIPLIER

BOARD . . . . . . . . . . . . . . . . . . . . LBI-30029

(DF1106)
IF AUDI O AND SQUELCH

BOARD . . . . . . . . . . . . . . . . . . . . LBI-38507

Ericsson Inc.

Private Radio Systems
Mountain V ie w Roa d
Lynchbur g, V ir ginia 24502
1-800-528-7711 (Outside USA, 804-528-7711) Printed in U.S.A.

LBI-38505 LBI-38505

TABLE OF CONTENTS

Page

SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

MODIFICATION INSTRUCTIONS (High Side Injection) . . . . . . . . . . . . . . . . . . . . . . . . 3

FRONT END ALIGNMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

ICOM FREQUENCY ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

COMPLETE RECEIVER ALIGNMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

TEST PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Audio Power Output And Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Usable Sensitivity (12 dB Sinad) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Modulation Acceptance Bandwidth (IF Bandwidth) . . . . . . . . . . . . . . . . . . . . . . . . . 8

TROUBLESHOOTING PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

ILLUSTRATIONS

FIGURE 1 - DISASSEMBLY PROCEDURE (Top View) . . . . . . . . . . . . . . . . . . . . . . . . 2

Squelch Sensitivity

Critical Squelch
Maximum Squelch

Frequency Stability

2C-ICOMs

Modulation Acceptance

Maximum Frequency Separation

406-470 MHz
470-494 MHz 1.50 MHz 2.0 MHz
494-512 MHz 1.50 MHz 2.0 MHz

Frequency Response

RF Input Impedance

*These specifications are intended primarily for the use of the serviceman. Refer to the appropriate Specifica tion Sheet for

the complete specifications.

Full Specifications 3 dB Degradation

1.60 MHz 2.0 MHz

Within +2 and -8 dB of a sta nd ard 6 dB per oc ta v e de-e mp has is cur v e fro m 300 t o
3000 Hz (1000 Hz reference)

50 ohms

0.25 µV0.1
Greater than 12 dB NQ (less than 1.0 µV)

0.0002% (-40°C to +70°C)

±

7 kHz (narrow-band)

±

V

µ

FIGURE 2 - RECEIVER BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

FIGURE 3 - DISASSEMBLY PROCEDURE (Bottom View) . . . . . . . . . . . . . . . . . . . . . . . 3

FIGURE 4 - RECEIVER MODULE LOCATION DIAGRAM . . . . . . . . . . . . . . . . . . . . . . 3

FIGURE 5 - TEST POINTS AND ALIGNMENT CONTROLS . . . . . . . . . . . . . . . . . . . . . . 4

FIGURE 6 - TEST SETUP FOR 20 Hz DOUBLE-TRACE SWEEP ALIGNMENT . . . . . . . . . . . . . . 4

FIGURE 7 - FREQUENCY CHARACTERISTICS vs. TEMPERATURE . . . . . . . . . . . . . . . . . . 5

SPECIFICATIONS*

Audio Output (to 8-ohm Speaker) 1 Watt at less than 3% distortion

Sensitivity

12 dB SINAD (EIA Method)
20 dB Quieting Method

SELECTIVITY

EIA Two-Signal Method (2 5 k H z Spacing) -90 dB -90 dB

Spurious Res po ns e -90 dB -100 dB

With Pre-Ampl Without Pre-Ampl

0.20 µV0.35

0.25 µV0.50

V

µ

V

µ

WARNING

Although the highest DC voltage in MASTR II receiv er is +12 Volts DC, high current may be drawn under short circuit
conditions. These currents can possibly heat metal objects such as tools, rings, watc hbands, etc., enough to cause burns.
Be careful when working near energized circuits!

High-level RF ener gy in the transmitte r Power Amplifier assembly can cause RF b u rns upon contact. Keep away from
these circuits when the transmitter is energized!

Intermodulation (EIA) -75 dB -80 dB

Copyright © May 1990, Ericsson GE Mobile Communications Inc.

1

LBI-38505 LBI-38505

DESCRIPTION

MASTR II Base Station, 40 6 to 512 mega hertz receivers
are single con version, superheter odyne FM receiv ers designed
for one-through eight-frequency operation. The solid state
receiver utilizes integrated circuits (ICs), monolithic crystal
filters and discrete components with each of the crystal filters
located between gain stages to provide 100 dB selecti vity a nd
maximum protection from de-sensitization and intermodula­tion.

The receiver consists of the following modules:

•

RF Assembly (Includes Mixer)

•

IF-Filter

•

Oscillator/Multiplier (Osc/Mult)

•

IF/Audio and Squelch (IFAS)

•

Optional Ultra-High Sensitivity

(UHS) Pre-Amplifier

Audio, supply voltages and control functions are con­nected to the system board through P903 on the Osc/Mult
board, and P904 on the IFAS board. The regulated +10 Volts
is used for all receiver stages except the audio PA stage which
operates from the A+ system su pp ly.

Centralized metering jack J601 on the IFAS board is pro­vided for use with Test Set 4EX3A11 or Test Kit 4EX8K12.
The test set meters the oscillator, multiplier, IF Detector and
IF amplifier stages. Speaker high and low are metered on the
system board metering jack.

Remove the top cover , then loosen the two bottom co ver
retaining screws and remove the bottom cover (see Fig­ure 1).

3. To gain access to the bottom of the Osc/Mult and IFAS
board, remove the six screws (A) holding the receiver
bottom cover (see Figure 3).

NOTE

Refer to Figure 4 for receiver module location.

To remove the OSC/Mult board from the radio:

1. Remove the six screws (A) holding the receiver bottom
cover.

2. Remove the eight screws (E ) holding the IF-Filter bottom
cover .

3. Remove the four screws (B) holding the board.

4. Press strai ght down on the plug-in Osc/Mu lt boar d from
the top to avoid bending the pins when unplugging th e
board from the syste m bo ard jack.

To remove the IFAS board from the radio:

1. Remove the six screws (A) holding the bottom cover, and
the one screw (C) holding the board.

A block diagram of the complete receiver is shown in

Figure 2.

Refer to the appropriate Maintenance Ma nual for complete

details on each receiver module listed in the Table of Contents.

MAINTENANCE

DISASSEMBL Y

To service the Receiver from the top (see Mechanical Parts
Breakdown):

1. Pull the locking handle down, then pry up the top cover
at the front notch and lift off the cover.

To service the Receiver from the bottom:

1. Pull the locking handle down and pull the radio out of
the mounting frame.

2.

2. Remove the two screws (D) holding the audio PA
heatsink to the right side rail.

Figure 2 - Receiver Block Diagram

Figure 1 - Disassembly Procedure

(T op V iew)

2

LBI-38505 LBI-38505

MODIFICATION INSTRUCTIONS

Figure 3 - Disassembly Procedure

(Bottom Vi ew)

To remove the IF Filter board from the radio:

1. Remove the eight screws (E) holding the IF Filter bottom
cover.

2. Remove the six screws (F) holding the IF Filter top cover.

3. Remove the thre e screws (G) and the Con nector (H), an d
carefully push down on the top of the board to avoid
damaging the feedthrough capacitors .

To remove the optional UHS pre-amplifier board:

1. Remove the eight screws (E) holding the IF Filter bottom
cover , and the six screws (F) holding the IF Filter top cover.

2. Disconnect the two connectors and 10 Volt lead (J).

3. Remove the three screws on the bottom side of the board,
and lift out the board.

MODIFICATION INSTRUCTIONS FOR UHF HIGH SIDE INJECTION APPLYING 19A130045G5 KIT. THIS
MODIFICATION IS NOT REQUIRED FOR RECEIVERS OPERATING IN THE FOLLOWING RANGES.

450 TO 458.8 MHz
470 TO 482.8 MHz
494 TO 500.8 MHz

1. FOR RECEIVERS OPER ATING BETWEEN 458.8 TO 470 MHz (OSC/MULT BD’S 19D423266G2 & G6):
A. IF THE RECEIVER HAS LESS THAN 8 ICOMS, REMOVE C407, C412, C417 .

REPLACE C407 WITH C2315 (13 pF, -N80). REPLACE C412 WITH C2316 (5pF, NPO).

B. IF THE RECEIVER HAS MORE THAN 8 ICOMS, REMO VE C407 , C41 2, C417 .

REPLACE C407 WITH C2317 (8pF, N80). REPLACE C412 WITH 2316 (5pF, NPO)

2. FOR RECEIVERS OPER ATING BETWEEN 482.8 TO 494 MHz (OSC/MULT BD’S 19D423266G3 & G7):
A. IF THE RECEIVER HAS LESS THAN 8 ICOMS, REMOVE C407, C412, C417 .

REPLACE C407 WITH C2318 (10pF, N80). REPLACE C412 WITH C2319 (4pF, NPO).

B. IF THE RECEIVER HAS MORE THAN 8 ICOMS, REMO VE C407 , C41 2, C417 .

REPLACE C407 WITH C2320 (6pF, N80). REPLACE C412 WITH C2319 (4pF, NPO).

3. FOR RECEIVERS OPER ATING BETWEEN 500.8 TO 512.0 MHz (OSC/MULT BD’S 19D423266G4 & G8):
A. IF THE RECEIVER HAS LESS THAN 8 ICOMS, REMOVE C407, C412, C417 .

REPLACE C407 WITH C2317 (8pF, N80). REPLACE C412 WITH C2321 (3pF, NPO).

B. IF THE RECEIVER HAS MORE THAN 8 ICOMS, REMO VE C407 , C41 2, C417 .

REPLACE C407 WITH C2316 (5pF, N80). REPLACE C412 WITH C2321 (3pF , NP0).

4. SOLDER ALL ELECTRICAL CONNECTIONS. DISCARD CAPACITORS NOT USED.

5. IN APPLICATION OF THIS KIT THE CRYSTAL OSCILLATOR FREQUENCY MUST BE CHANGED PER THE
FOLLOWING FORMULA:

FX= Fo + 11.2

27

6. MARK ALL OSC/MUL T BD’S (19D42 3266) WITH A BLUE COLOR DOT IN T HE AREA OF THE PL DRAWING NO.
PER 19A115740P1.

7. APPLY LABEL (19A130206P3) TO SIDE OF PLASTIC FRAME.

8. TEST AND ALIGN PER NORMAL PROCEDURE.

Figure 4 - Receiver Module Location Diagram

HIGH SIDE INJECTION

3

LBI-38505 LBI-38505

FRONT END ALIGNMENT

EQUIPMENT REQUIRED

1.

Test Set Models 4EX3A11, 4EX8K12, or 20,000 ohms-per-Volt multimeter with a 1 V olt scale.

2.

A 406-512 MHz signal source.

PRELIMINAR Y CHECKS AND ADJUSTMENTS

1.

Connect black plug from Test Set to Receiver Centralized Metering Jack J601, and red plug to system boa rd metering jac k J905. Set met er sensitivity
switch to the TEST 1 position (or 1-Volt position on 4EX8K12).

2.

For multi-frequency receivers with a frequency spacing up to 0.800 MHz for frequency range of 406-470 MHz, 0.900 MHz for frequency range of 470-494
MHz or 0.750 MHz for frequency range of 494-512 MHz, align the receiver on the channel nearest center frequency.

For multi-frequency receivers with a frequency spacing exceeding the above but no greater than 1.60 MHz for frequency range of 406-470 MHz, 1.80
MHz for frequency range of 470-494 MHz, or 1.50 MHz for frequency range of 494-512 MHz, align the receiver using a center frequency tune-up ICOM.
These limits can be extended to 2.00 MHz, 2.30 MHz and 2.00 MHz respectively, with 3 dB degradation in standard receiver specifications.

3.

With Test Set in Position J, check for regulated +10 Volts. If using multimeter, measure between J905-3 (+) and J905-9 (-).

4.

If using multimeter, connect the negative lead to J601-9 (A-).

5.

Disable Channel Guard.

ALIGNMENT PROCEDURE

METERING POSITION

STEP SET METERING -AT J601-9 CONTROL READING PROCEDURE

TEST INTERNAL MULTIMETER TUNING METER

OSCILLATOR/MULTIPLIER

1. C
(MULT-1)3(MULT-1)

2. C411, C416,

3. D
(MUL T-2)4(MUL T-2)

4. F
(MULT-3)5(MULT-3)

NOTE: IF AMP meter range is 0-700 mVdc with a high impedance DC voltmeter.

5. B 2

(IF AMP)

Pin 3 C406 Maximum Tune C406 for maximum meter reading.

See
C306, C307 and
C308

Pin 4 C411, C416,

C406

Pin 7 C306, C307 &

C308

Pin 1 C301 thru C305,

A303-C2, (and
L2301 if pres ent)

Procedure

See

Procedure

See

Procedure

RF SELECTIVITY

Maximum Apply an on-frequency signal to antenna jack, keeping the signal

Preset C411 and C416 to a positi on similar to C406. Next, preset
C306, C307 and C308 fully counterclockwise. (Minimum capacity.)

Tune C411 and C416 for maximum meter reading. Next, retune
C406, C411 and C416 for maximum meter reading. Then carefully
tune C306 for a change in meter reading (peak or dip).

Carefully tune C307 and C306 for maximum meter reading. Repeat
the procedure. Next, carefully tune C308 for minimum meter
reading, and retune C306 for maximum meter reading. Do
readjust C307 and C308.

below saturation. Then tune C301 through C305 and A303-C2 for
maximum meter reading. In receivers with the UHS preamplifier,
also tune L2301 for maximum meter reading.

Figure 5 - T e st Points And Alignment Controls

NOT

6. B 2
(IF AMP)

Pin 1 C301 thru C305,

A303-C2, C306,
C307 and C308
(L2301 if present)

406-512 MHz MASTR II RECEIVER

4

Maximum Apply an on-frequency signal to the antenna jack and slightly tune

C301 through C305, A303-C2, (L2301 if present) for best quieting
sensitivity. C306, C307 and C308 also may be tuned slightly (not to
exceed 1/4 turn).

Figure 6 - Test Setup For 20 Hz Double-Trace Sweep Alignment

LBI-38505 LBI-38505

ICOM FREQUENCY ADJUSTMENT

First, check the frequency to determine if any adjustment is required. The frequency measurement requires equipment with an
absolute accuracy which is 5 to 10 times better than the tolerance to be maintained. When performing frequency measurement, the
entire radio should be as near as possible to an ambient temperature of 26.5°C (79.8°F).

MASTR II ICOMs should be reset only when the measured frequency error exceeds the following limits.

A.

±0.5 PPM, when the radio is at 26.5°C (79.8°F).

B.

±2 PPM at any other temperature within the range -5°C to +55°C (+131°F).

C.

The specification limit (±2 PPM or ±5 PPM) at any temperature within the ranges -40°C to -5°C (-40°F to +23°F) or +55° to
+70°C (+131°F to +158°F).

If frequency adjustment is required, lift up the cover on the top of the ICOM (where present) to expose the adjustment trimmer.
Depending upon the type of frequency measuri ng equ i pm en t that i s available, a n y of the following procedures may be used:

DIRECT MEASUREMENT IN THE INJECTION CHAIN

A.

1. WITH A FREQUENCY COUNTER. "Count" the frequency at the junction of C416 and L4 03 on the Oscillator/Multiplier
Board. The frequency measured at this point is 9 times the ICOM frequency. NOTE: The output from the ICOM itself is
not sufficiently sinusoidal for reliable operation with most frequency counters.

2. WITH A COMMUNICATION MONITOR (for e xam ple: Cushm an Mo de l CE- 3). "Moni tor" f re quen cy a t the j uncti on of
C416 and L403 on the Oscillator/Multiplier Board. The frequency monitored at this point is 9 times the ICOM frequenc y.
NOTE: This frequency will not always fall within an available measuring range of all monitors at all receiver operating
frequencies.

STANDARD "ON FREQUENCY" SIGN AL AT THE RECEIVER INPUT (Generated from a COMMUNICATION MONI-

B.

TOR, for example: Cushman Model CE-3).

The frequency of the "beat" is the frequency error, related to the IF frequency. This deviation, in Hz, is compared to the

receiver oper ating freque ncy, also in Hz, to calculate the err or in PPM.

NOTE

The FM Detector output (meter position A of the test set) has a DC voltage of +0.35 to 0.5-Volts with an
ON-FREQUENCY signal or under NO-SIGNAL conditions and is provided for routine test and measurement only. The
resolution of this reading (approximately .025 V per kHz as read on a Test Set in meter position A, or 0.1 V per kHz as
measured with a VTVM at P904-3 or J601-2 on the IFAS board) is ina dequate for oscillator frequency setting.

If the radio is at an ambient temperature of 26.5°C (79.8°F), set the oscillator for the correct mixer frequency (ICOM FREQ.

X 9).

If the radio is not an ambient temperature of 26.5°C, setting errors can be minimized as follows:

A.

To hold setting error to ±0.6 PPM (which is considered reasonable for 5 PPM ICOMS):

1.

Maintain the radio at 26.5°C (±5°C) and set the oscillator to require mixer injection frequency, or

2.

Maintain the radio at 26.5°C (±10°C) and offset the oscillator, as a function of actual temperature, by the frequency
error factor shown in Figure 7.

B.

To hold setting error to ±0.35 PPM (which is considered reasonable for 2 PPM ICOMS): Maintain the unit at 26.5°C
(±5°C) and offset the oscillator, as a function of actual temperature, by the frequency error factor shown in Figure 7.

For example: Assume the ambient temperature of the radio is 18.5°C (65.4°F). At that temperature, the curve shows a

correction factor of 0.3 PPM. (At 138 MHz, 1 PPM is 138 Hz. At 174 MHz, 1 PPM is 174 Hz).

With a mixer injection of 150 MHz, adjust the oscillator for a corrected mixer injection frequency 45 Hz (0.3 X 150 Hz)
higher. If a ne gative correction factor is obtained (at temperatures above 26.5°C), set the oscillator for the indicated PPM lower
than the calculated mixer injection frequency.

1. WITH A FREQUENCY COUNTER. "Count" the dev elo ped I F freq ue nc y at the top of Z6 02-R2 on th e IFAS board. The
deviation from the nominal IF frequency (11.2 MHz) in Hz is compared to the receiver operating frequency (also in Hz)
to calculate error in PPM.

2. WITH AN 11.2 MHz IF FREQUENCY STANDARD (for example: Model 4EX9A10). Loosely couple the IF frequency
standard to the IF signal path to create a heterodyne with the developed IF frequency. The resultant "beat frequency" can
be monitored by either of the following methods:

a. Audible "beat frequency" from the receiver speaker (this requires careful frequency adjustment of the frequency standard).

NOTE

T o SET ICOM frequenc y using "be at frequenc y" metho d, the tempe rature shoul d be at 26.5°C (79. 8°F). If t he temperat ure
is not 26.5°C, then offset the "on frequency" signal (at the receivers input), as a function of actual temperature, by the
frequency error factor (in PPM) shown in Figure 7.

b. Observe "beat frequency" at P904-4 with an Oscilloscope.
c. With TEST SET (Meter Position B) connected to J601 on the IFAS Board, visually observe the "beat frequency" indicated

by meter movement.

Figure 7 - Frequency Characteristics Vs. Temperature

406-512 MHz MASTR II RECEIVER

5

LBI-38505 LBI-38505

ALIGNMENT PROCEDURES

COMPLETE RECEIVER ALIGNMENT

EQUIPMENT REQUIRED

1.

Test Set Models 4EX3A11, 4EX8K12, or 20,000 ohms-per Volt multimeter with a 1- Volt scale.

2.

An 11.2 MHz signal source (Test Set Model 4EX9A10). Also a 406-512 MHz s ignal source with a one-inch piece of insulated wire no larger than .065
inch diameter connected to generator probe.

3.

DVM.

4.

Distortion Analyzer.

PRELIMINARY CHECK S AND ADJUSTMENTS

1.

Connect the black plug from the Test Set to receiver metering jack J601, and the red plug to system board metering jack J905. Set the meter sensitivity
switch to the Test 1 (or 1- Volt position on the 4EX8K12).

For multi-frequency receivers with a frequency spacing up to 0.800 MHz for frequency range of 406-470 MHz, 0.900 MHz for frequency range of
470-494 MHz, or 0.750 MHz for frequency range of 494-512 MHz, align the receiver on the channel nearest center frequency.

For multi-frequency receivers with a frequency spacing exceeding the above but no greater than 1.60 MHz for frequency range of 406-470 MHz, 1.80
MHz for frequency range of 470-494 MHz, or 1.50 MHz for frequency range of 494-512 MHz, align the receiver using a center frequency tune-up ICOM.
These limits can be extended to 2.00 MHz, 2.30 MHz and 2.00 MHz respectively, with 3 dB degradation in standard receiver specifications.

3.

With the T est Set in Position J, check for regulated +10 Volts. With multimeter, measure from J905-3 to J905-9.

4.

If using multimeter, connect the negative lead to J601-9 (A-)

5.

Disable the Channel Guard.

ALIGNMENT PROCEDURE

METERING POSITION

TEST INTERNAL MULTIMETER TUNING METER

STEP SET METERING -TO J601-9 CONTROL READING PROCEDURE

FM DETECTOR

1. A
(FM DET)1(FM DET)

2. C

(MULT-1)3(MULT-1)

3. C411, C416,

4. D

(MULT-2)4(MULT-2)

5. F

(MULT-3)5(MULT-3)

Pin 2 L603 0.38 Vo lt With no signal applied, adjust L603 for a meter reading of

approximately 0.38 V olt.

OSCILLATOR/MULTIPLIER

Pin 3 C406 Maximum Tune C406 for maximum meter reading.

C306, C307
and C308

Pin 4 C411, C41 6,

C406

Pin 7 C306, C30 7

and C308

See

Procedure

See

Procedure

See

Procedure

Preset C411 and C416 to a position similar to C406. Next,
preset C306, C307 and C308 fully counterclockwise
(minimum capacity).

Tune C411 and C416 for maximum meter reading. Next, retune
C406, C411 and C416 for maximum reading. Then carefully
tune C306 for a change in meter reading (peak or dip).

Carefully tune C307 and C306 for maximum meter reading.
Repeat the procedure. Next carefully tune C308 for minimum
meter reading. Do

NOT readjust C307 and C308.

METERING POSITION

TEST INTERNAL MULTIMETER TUNING METER

STEP SET METERING -AT J601-9 CONTROL READING PROCEDURE

RF AMP & SELECTIVITY

NOTE: IF AMP meter range is 0-700 mVDC with a high impedance DC voltmeter.

6. B
(IF AMP)2 (IF AMP)

7. B
(IF AMP)2(IF AMP)

8. B
(IF AMP)2(IF AMP)

9. B
(IF AMP)2(IF AMP)

10. B
(IF AMP)2(IF AMP)

11. L603, R609 See

The mixer and IF circuits have been aligned at the factory and will normally require no further adjustment. If adjustment is necessary, use the procedure out­lined in STEP 13.

Pin 1 C305, C304

and A303-C2

Pin 1 C304 and C303 Maximum Apply an on-frequency signal in the hole adjacent to C303,

Pin 1 C303 and C302 Maximum Apply an on-frequency signal in the hole adjacent to C302,

Pin 1 C301 thru C305,

A303-C2 (and
L2301 if pres ent)

Pin 1 C301 thru C305,

A302-C2, C306,
C307 & C308
(L2301 if present)

Maximum Preset A303-C2 to mid position. Apply an on-frequency signal in

the hole adjacent to C304, keeping the signal below saturation.
Then tune C305, C304 and then A303-C2 for maximum meter
reading.

keeping the signal below saturation. Then tune C304 and C303
for maximum meter reading.

keeping the signal below saturation. Then tune C303 and then
C302 for maximum meter reading.

Maximum Apply an on-frequency signal to the antenna jack, keeping the

signal below saturation. Then tune C301 through C305 and A303­C2 for maximum meter reading. In receivers with the UHS
preamplifier, also tune L2301 for maximum meter reading.

Maximum Apply an on-f requency signal to th e antenna jack an d slightly tune

C301 through C305, A303-C2 (and L2301 if present) for best
quieting sensitivity. C306, C307 & C308 also may be tuned
slightly not to exceed 1/4 turn).

Remove the Test set metering plug from J601. Apply a 1000

Procedure

MIXER & IF

microvolt signal w ith 1 kHz m odulation and 3 kHz de viation to th e
antenna jack. Tune L603 for maximum voltage at 1.0 kHz and
adjust R609 for 1 Volt RMS measured with a DVM at P904-11
(VOL/SQ HI) and P904-17 (A-).

NOTE

Refer to DATAFILE BULLETIN 1000-6 (IF Alignment of Two-Way Radio FM
Receivers) for helpful suggestions on how to deter mine when IF Alignment is required.

12. L507, L503, L504 and C504,

T601, T602, and T603

Connect scope, signal generator, and probe as shown in Figure 6.
Set signal generator level for 3 to 5 µV and modulate with 20 Hz
at 12 kHz deviation. With probe between P904-4 (or J601-1) and
A-, tune L507, L503, L504, C504, T601, T602, and T603 for
double trace as shown on scope pattern. Preset T601-T603 to top
of coil form before tuning.

Cont’d.

13. See

Procedure

Check to see that modulation acceptance bandswidth is greater
than ±7 kHz.

406-512 MHz MASTR II RECEIVER

6

LBI-38505 LBI-38505

TEST PROCEDURES

TEST PROCEDURES

These Test Procedures are designed to help you to service a
receiver that is operating---but not properly. The problems en­countered could be low power , poor sensitivity , distortion, limiter
not operating properly , and low gain. By following the sequence
of test steps starting with Step 1, the defect can be quickly
localized.

TEST EQUIPMENT REQUIRED

•

Distortion Analyzer similar to:
HP331A, or an equivalent aver age response meter

•

Signal Generator similar to:
HP8640B

•

6-dB attenuation pad, and 8.0 ohm, 2-Watt resistor

Once the defective stage is pin-pointed, refer to the "Service
Check" listed to correct the problem. Additional corrective meas­ures are included in the Troubleshooting Procedure. Before
starting with the Receiver Test Procedures, be sure the receiver
is tuned and aligned to the proper operating frequency.

PRELIMINAR Y ADJUSTMENTS

1. Connect the test equipment to the receiver as sho wn f or all

steps of the receiver Test Procedure.

2. Turn the SQUELCH control fully clockwise for all steps of

the Test Procedure.

3. Turn on all of the equipment and let it warm up for 20

minutes.

STEP 1

AUDI O POWER OUTPUT AND DISTORTION

TEST PROCEDURE

Measure Audio Power Outp ut as follo ws:

A. Apply a 1,000 microvolt, on frequency test signal modulated by 1,000 Hertz with 3.0 kHz deviation to antenna jack A301-J1.

B. Disconnect speaker lead pin from System Plug P701-11 (on rear of Co ntrol Unit).

Connect an 8.0-ohm, 2-Watt load resistor from P904-19 (SPKR H1) to P904-18 (SPKR LO) or from P701-4 to P701-17

(SPKR HI) on the System Plug. Connect the Distortion Analyzer input across the resistor as shown.
OR WITH HANDSET:
Lift the handset off of the hookswitch. Connect the Distortion Analyzer input from P904-19 to P904-18.

C. Adjust the VOLUME control for one W att output using the Distortion Analyzer as a Voltmeter.

D. Make distortion measurements according to manufacturer’s instructions. Reading sho uld be less than 3%. If the receiver

sensitivity is to be measured, leave all controls and equipment as they are.

SERVICE CHECK

If the distortion is more than 3%, or maximum audio output is less than 1 Watt, make the follo wing che cks:

E. Powe r Supply and regulator voltage---low voltage will cause distortion. (Refer to Receiver Sc hematic Diagram for voltages.)

F. Audio Gain (Refer to Recei ver Trouble s ho oti n g P rocedure.)

G. FM Detector Alignment (Refer to Receiver Alignment.)

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LBI-38505 LBI-38505

TEST PROCEDURESTEST PROCEDURES

TROUBLESHOOTING PROCEDURES

STEP 2

USABLE SENSITIVITY

(12 dB SINAD)

If STEP 1 checks out properly, measure the receiver sensitivity as follows:

A. Apply a 1000 microvolt, on frequency signal modulated by 1000 Hz with 3.0 kHz deviation to A301-J1.

B. With Function Switch on Distortion Analyzer set to VOLTMETER position, adjust volume control for 1.0 W att (2.83 VRMS

across 8 ohm load). Again, verify that audio output is nulled when Function Switch is set to DISTORTION position.

C. Place the RANGE switch to the SET LEVEL position (filter out of the circuit) and adjust the input LEVEL control for a

+2 dB reading on a 30% range.

D. While reducing the signal generator output, switch the FUNCTION control from SET LEVEL to the DISTORTION until

a 12 dB difference (+2 dB to -10 dB) is obtained between the SET LEVEL and DISTORTION positions (filter out and filter
in).

E. The 12 dB difference (Signal plus Noise and Distortion to noise plus distortion ratio) is the "usable" sensitivity level. The

sensitivity should be less than rated 12 dB SINAD specifications with an audio output of watt across the 8.0 ohm load.

F. Lea ve all controls as they are and all equipment connected if the Modulation Acceptance Bandwidth test is to be performed.

SERVICE CHECK

If the sensitivity level is m ore than the rated 12 dB SINAD specification, check the alignment of the RF stages as directed in the
Alignment Procedure, and make the gain measurements as shown on the Troubleshooting Procedure.

STEP 3

MODULATION ACCEPTANCE

BANDWIDTH (IF BANDWIDTH)

If STEPS 1 and 2 check out properly, measure the bandwidth as follows:

A. Set the Signal Generator output for twice the microvolt reading obtained in the 12- dB SINAD measurement.

B. Set the RANGE control on the Distortion Analyzer in the SET LEVEL position (1000-Hz filter out of the circuit), and

adjust the input LEVEL control for a +2 dB reading on the 30% range.

C. While increasing the deviation of the Signal Generator, switch the RANGE control from SET LEVEL to distortion range

until a 12- dB difference is obtained between the SET LEVEL and distortion range readings (from +2 dB to -10 dB).

D. The deviation control reading for the 12- dB difference is the Modulation Acceptance Bandwidth of the receive r. It should

be more than ±7 kHz.

SERVICE CHECK

STEP 1 - QUICK CHECKS

TEST SET CHECKS

These checks are typical readings measured with Test Set Model 4EX3A11 in the Test 1 position, or Model 4EX8K12 in the
1-Volt position.

METERING READING READING WITH- TEST
POSITION WITH NO 10 MICROVOLTS POSITION

SIGNAL IN (UNMODULATED)

A (FM DET) Approximately Test 1

B (IF Amp) 0.1 VDC
C (Mult-1) 0.4 VDC
D (Mult-2) 0.4 VDC
F (Mult-3) 0.1 VDC
J (Reg. +10 Volt at +10 VDC

System Metering

SYMPTOM PROCEDURE

NO SUPPLY VOLT A GE

NO REGULATED 10-VOLTS

LOW IF READING

LOW OSCILLATOR/MULTIPLIER READINGS

LOW RE CEIVER SENSITIVITY

0.38 VDC (or 1 Volt)

SYMPTOM CHECKS

• Check power connections, continuity of supply leads . Check fuse

and replace if blown. Check receiver for short circuits.

• Check the 12 Volt supply. Then check 10 Volt regulator circuit.

(See Troubleshooting Procedure for 10 Volt Regulator).

• Check supply voltages and then check oscillator readings at

P904-1 & -2 as shown in STEP 2.

• Make SIMPLIFIED GAIN CHECKS from Mixer through

Limiter Detector stages as shown in STEP 2.

• Check alignment of Oscillator/Multipli er chain. (Refer to Front

End Alignment Procedure).

• Check voltage readings of Oscillator/Multiplier chain (Q401,

Q402, Q403).

• Check Front End Alignment. (Refer to Receiver Alignment

Procedure).

• Check antenna connections, cable and antenna switch.

• Check Oscillator injection voltage.

• Check voltage readings of IF Amplifiers.

• Make SIMPLIFIED GAIN CHECKS (STEP 2).

If the Modulation Acceptance Bandwidth test does not indicate the proper width, make gain measurements as shown on the
Receiver Troubleshooting Procedure.

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Con’t.

406-512 MHz MSTR II RECEIVER

LBI-38505 LBI-38505

TROUBLESHOOTING PROCEDURES

SYMPTOM CHECKS Con’t.

SYMPTOM PROCEDURE

IMPROPER SQUELCH OPERATION

LOW OR DISTORTED AUDIO

NOISE SQ OUTPUT U605-2

CAS U605-1

• Check voltages on Schematic Diagram.

• Make gain and waveform checks with noise.

• Make gain and waveform checks with 6 kHz signal.

• Check discrete components in the squelch circuit.

• Replace IC circuit U603.

• Check voltages on Schematic Diagram.

• Make gain and waveform checks.

• Check receiver alignment and FM -DET output.

• Check Q601, Q602, Q605 and other discrete components.

SQUELCH CHECKS

SQUELCHED UNSQUELCHED

0.2 VDC 9.9V

0.1 VDC 9.9V

RX MUTE U605-14

RUS U605-13

SQ DISABLE SW. INPUT U606-1

AUDI O GATE SW. CONTROL U606-11

If External Decoder is used (CG, DCG, Type 99, etc.),

response is decoded.

In above cases,

is unsquelched for all conditions.

RX Mute = Noise Sq Output• Decoder Output.

Sq Disable is assumed high (9.9V). If Sq Disable is grounded, U606-10 = 0.2 Vdc, U606-11 = 9.9 Vdc and Unit

0.2 VDC 9.9V

0.2 VDC 4.9V

0.2 VDC 9.9V

0.2 VDC 9.9V

RX Mute will remain low (regardless of noise squelch output), until proper

9

LBI-38505 LBI-38505

TROUBLESHOOTING PROCEDURES

406-512 MHz MASTR II RECEIVER

10

LBI-38505 LBI-38505

TROUBLESHOOTING PROCEDURES

406-512 MHz MASTR II RECEIVER

11