Motorola PM400 Service Manual Page 178
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Receive Audio Circuits 2-19
9.0 Receive Audio Circuits
Figure 2-9 Receive Audio Paths
9.1 Squelch Detect
The radio’s RF circuits are constantly producing an output at the discriminator (IF IC). This signal
(DISC AUDIO) is routed to the ASFIC CMP’s squelch detect circuitry input DISC (U504-pin 2). All of
the squelch detect circuitry is contained within the ASFIC CMP. Therefore from a user’s point of
view, DISC AUDIO enters the ASFIC CMP, and the ASFIC CMP produces two CMOS logic outputs
based on the result. They are CH ACT (U504-16) and SQ DET (U504-17).
The squelch signal entering the ASFIC CMP is amplified, filtered, attenuated, and rectified. It is then
sent to a comparator to produce an active high signal on CH ACT. A squelch tail circuit is used to
produce SQ DET (U504-17) from CH ACT. The state of CH ACT and SQ DET is high (logic “1”)
when carrier is detected, otherwise low (logic “0”).
CH ACT is routed to the µP pin 84 while SQ DET is routed to the µP pin 83.
SQ DET is used to determine all audio mute / unmute decisions except for Conventional Scan. In
this case CH ACT is a pre-indicator as it occurs slightly faster than SQ DET.
FLT RX AUDIO
P1
11
16
1
EXTERNAL
SPEAKER
INTERNAL
SPEAKER
ACCESSORY
CONNECTOR
CONTROL HEAD
CONNECTOR
HANDSET
AUDIO
18
20
19
J2
INT
SPKR-
SPKR +
SPKR -
1
9
2
U509
4110
INT
SPKR+
4
6
DISC
ASFIC_CMP
U504
AUDIO
PA
U502
VOLUME
ATTEN.
FILTER AND
DEEMPHASIS
17
MICRO
CONTROLLER
U403
80
FROM
RF
SECTION
(IF IC)
LIMITER, RECTIFIER
FILTER, COMPARATOR
SQ DET
SQUELCH
CIRCUIT
16
PL FILTER
LIMITER
CH ACT
AUX RX
43
18
LS IO
U IO
AUDIO
83
84
39
URX OUT
DISC
AUDIO
37
85
GCB4
MUTE
GCB1
14
U505
- Foreword 3
- Document Copyrights 3
- Disclaimer 3
- SAFETY INFORMATION 10
- Chapter 1 12
- INTRODUCTION 12
- 3.2 Motorola Online 13
- 3.3 Mail Orders 13
- 3.4 Telephone Orders 13
- 3.5 Fax Orders 13
- 4.0 Radio Model Information 14
- 1-4 INTRODUCTION 15
- Chapter 2 16
- MAINTENANCE 16
- 2-2 MAINTENANCE 17
- 2-4 MAINTENANCE 19
- 2-6 MAINTENANCE 21
- 2-8 MAINTENANCE 23
- SERVICE AIDS 24
- 2.0 Test Equipment 25
- OVERVIEW 30
- 1-2 OVERVIEW 31
- 2.3 Keypad Keys 33
- 2.6 Speaker 34
- 3.1 Power Supplies 35
- 3.2 SPI Interface 35
- 3.3 Keypad Keys 36
- 3.4 LCD Driver 36
- 3.7 Speaker 37
- (see table on next page) 39
- Key_Row Voltage TP402 40
- 2.1 Control Head Failure 41
- SHOWN FROM SIDE 1 46
- Control Head CM200 Schematic 47
- Bottom Side 49
- Top Side 49
- UHF2, 1-25 W, 438-470 MHz 58
- mP U403 90
- OL 79B02969C76-O 97
- OL 79B02969C78-O 97
- SHOWN FROM SIDE 2 98
- OL 79B02969C77-O 98
- OL 79B02969C79-O 98
- DC & AUDIO 100
- SHEET 2 OF 8 102
- 73D02968C74-O 102
- FRACN_63A27 103
- SHEE 5 OF 8 104
- TO SHEET 1 105
- SHEET 6 OF 8 106
- SHEET 7 OF 8 108
- SHEET 8 OF 8 110
- SHEET 3 OF 8 111
- List 1-25 W 112
- COMPARTMENT 123
- Option Board 126
- Keypad/Display 126
- CM200/CM300/PM400 150
- Computer Software Copyrights 151
- Table of Contents 152
- UHF2, 25-40 W, 438-470 MHz 156
- 2.0 Technical Specifications 157
- Transmitter 158
- Receiver 158
- THEORY OF OPERATION 160
- 2.2 Receiver Back End 161
- 3.3 Final Stage 162
- 3.4 Directional Coupler 162
- 3.5 Antenna Switch 162
- 3.6 Harmonic Filter 163
- 3.7 Power Control 163
- 4.1 Reference Oscillator 163
- 4.2 Fractional-N Synthesizer 164
- 4.4 Synthesizer Operation 166
- 5.1 Radio Power Distribution 167
- 5.2 Protection Devices 169
- 5.3 Automatic On/Off 169
- 5.6 SBEP Serial Interface 171
- 2-14 THEORY OF OPERATION 173
- 7.0 Transmit Audio Circuits 174
- 2-16 THEORY OF OPERATION 175
- 8.1 Sub-Audio Data (PL/DPL) 176
- 8.2 High Speed Data 177
- 9.1 Squelch Detect 178
- 2-20 THEORY OF OPERATION 179
- 9.4 Handset Audio 180
- 10.2 Alert Tone Circuits 181
- Chapter 3 182
- TROUBLESHOOTING CHARTS 182
- uP U403 188
- 3-8 TROUBLESHOOTING CHARTS 189
- Chapter 4 192
- Internal SPKR+ Jumper 197
- MRF1513’s Thermal pad 199
- LVFRACN Shield 201
- VCOBIC Shield 202
- FRONT-END SHIELD 203
- MIXER SHIELD 203
- IFAMP_DEC1 204
- IFAMP_DEC2 204
- AUDIOOUT 204
- AUDIO_FEED 204
- POWER SUPPLY 205
- TO SHEET 2 208
- UHF3, 25-40 W, 465-495 MHz 256
- VCOBIC Shield 330
- VCO Shield 330
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