Motorola Two Way Portable Radio Ht750ls Detailed 6881088c46 E Manual

MANUAL REVISION
12-26-03
®
© Motorola, Inc. 2003
8000 West Sunrise Boulevard
Fort Lauderdale, Florida 33322
*FMR2045A-2*
FMR-2045A-2
HT Series, MTX Series, PRO Series
Professional Series
Two-Way Portable Radios
Detailed Service Manual
6881088C46-E
REVISION CHANGE:
This manual revision contains theories of operation, schematics, board layouts, and troubleshooting 
flowcharts for Professional Series radios with the following boards installed:
Use the information provided in this manual revision to...

December 26, 2003 2 FMR-2045A-2
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Table of Contents
REVISION CHANGE: ................................................................................................................................. 1
Chapter 1 UHF Theory of Operation ............................................................................... 7
1.1 Transmitter........................................................................................................................................ 7
1.1.1 General...

4Table of Contents
December 26, 2003FMR-2045A-2
5.1 Notes For All Schematics and Circuit Boards .................................................................................45
5.2 Circuit Board/Schematic Diagrams and Parts List .......................................................................... 47
Chapter 6 UHF Band 2 Troubleshooting Charts .......................................................... 61
6.1 Troubleshooting Flow Chart for Controller...

Table of Contents5
FMR-2045A-212/26/03
List of Figures
Transmitter Block Diagram .................................................................................................................. 7
UHF Receiver Block Diagram .............................................................................................................. 9
Frequency Generation Unit Block Diagram ....................................................................................... 10
Synthesizer Block Diagram...

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FMR-2045A-2December 26, 2003
UHF Theory of Operation: Transmitter7
Chapter 1 UHF Theory of Operation
1.1 Transmitter
Figure 1-1.  Transmitter Block Diagram
1.1.1 General
(Refer to Figure 1-1.)
The UHF transmitter contains five basic circuits:
 Power amplifier
 Antenna switch
 Harmonic filter
 Antenna matching network
 Power control integrated circuit (PCIC)
1.1.2 Power Amplifier
The power amplifier consists of two devices:
 9Z67 LDMOS driver IC (U101)
 PRF1507 LDMOS PA (Q110)
The 9Z67 LDMOS driver...

December 26, 2003FMR-2045A-2
8UHF Theory of Operation: Transmitter
1.1.3 Antenna Switch
The antenna switch circuit consists of two PIN diodes (CR101 and CR102), a pi network (C107, 
L104 and C106), and two current limiting resistors (R101, R170). In the transmit mode, B+ at PCIC 
(U102) pin 23 will go low and turn on Q111 where a B+ bias is applied to the antenna switch circuit to 
bias the diodes “on.” The shunt diode (CR102) shorts out the receiver port, and the pi network, which 
operates as a quarter...

FMR-2045A-2December 26, 2003
UHF Theory of Operation: Receiver9
1.2 Receiver
Figure 1-2.  UHF Receiver Block Diagram
1.2.1 Receiver Front-End
(Refer to the UHF Receiver Front-End Schematic Diagram on page 20 and the UHF Transmitter 
Schematic Diagram on page 25.)
The RF signal is received by the antenna and applied to a low-pass filter. For UHF, the filter consists 
of L101, L102, C102, C103, C104. The filtered RF signal is passed through the antenna switch. The 
antenna switch circuit consists of two...

December 26, 2003FMR-2045A-2
10UHF Theory of Operation: Frequency Generation Circuitry
The output of the post-RF amplifier filter which is connected to the passive double balanced mixer 
consists of T301, T302 and CR306. Matching of the filter to the mixer is provided by C381. After 
mixing with the first LO signal from the voltage controlled oscillator (VCO) using low side injection, 
the RF signal is down-converted to the 44.85 MHz IF signal. 
The IF signal coming out of the mixer is transferred to the...