Manuals / EFJohnson / Home Audio / Speaker

EFJohnson 761X, 764X service manual 4Second IF System IC1 UHF

Models: 761X 764X

1 99

Download 99 pages 7.65 Kb

Page 51

Figure 5-4 Second IF System IC1 (UHF)

UHF (7640) CIRCUIT DESCRIPTION

Figure 5-4 Second IF System IC1 (UHF)

Figure 5-5 Audio Switching and Amplifier Circuit (UHF)

and applied to the limiter amplifier and quadrature detector. The quadrature detector demodulates the audio signal contained in the second IF signal. Com- ponents connected to pins 10 and 11 including X1 are part of the quadrature detector. The audio signal is fed out on pin 9 (IC1) and applied to the AF amplifier circuit.

5.5.5 AUDIO AMPLIFIER CIRCUIT

The AF (audio frequency) amplifier circuit pro- vides drive to the speaker (see block diagram in Figure 5-5). The audio signal from IC1, pin 9 is applied to AF amplifier IC7b and then fed to high-pass filter IC6c/ IC6d. The cut-off frequency of this filter is controlled by the “AFHPF” line. When “AFHPF” is high, the cut-off frequency is shifted higher to attenuate the Call Guard (CTCSS or DTCS) signals.

The filtered output signal on IC6d, pin 14 is applied to pin 8 of AF switching circuit IC11. The switched output signal on IC11, pin 9 is then applied to pin 16 of level controller IC12. This device allows the CPU to control the speaker volume level. The vol- ume controlled output on pin 15 is then applied to pin 2 of AF switching circuit IC11. The switched output on pin 1 is applied to pin 4 of de-emphasis circuit IC4a. The signal is then amplified by IC9 to provide drive to the speaker.

5.5.6 RECEIVER MUTE CIRCUIT

Noise Squelch

The noise squelch circuit turns off the audio sig- nal when no RF signal is being received. The squelch circuit is controlled by the amount of noise present in the audio signal.

November 1998
Part No. 001-7600-001	5B-8

Image 51

EFJohnson 761X, 764X service manual 4Second IF System IC1 UHF

Contents

Part No. 761x VHF 764x UHF Conventional MobileVHF 146-174MHz 45 Watts Part No. UHF 400-430, 450-470, 490-512MHz 35 Watts761x VHF 764x UHF CONVENTIONAL FM TWO-WAYRADIO VHF 146-174MHz 45 WattsUHF 400-430, 450-470, 470-490,or 490-512MHz 35 Watts3 OPERATION TABLE OF CONTENTS2 INSTALLATION AND DISASSEMBLY 1 GENERAL INFORMATION5A VHF 7610 CIRCUIT DESCRIPTION TABLE OF CONTENTS CONT’D6 ADJUSTMENT PROCEDURE 7 PARTS LISTTABLE OF CONTENTS CONT’D 8SCHEMATIC DIAGRAMS AND COMPONENT LAYOUTSLIST OF TABLES LIST OF FIGURESSECTION 1 GENERAL INFORMATION 1.3 PRODUCT WARRANTY1.6 ACCESSORIES 1.7 FACTORY CUSTOMER SERVICEToll-Free:800 Table 1-175xx Accessories1.8 FACTORY RETURNS Accessory1.10 INTERNET HOME PAGE 1.9 REPLACEMENT PARTSThis page intentionally left blank NovemberPart No. GENERAL 7610 VHF AND 7640 UHF MOBILE SPECIFICATIONSNovember NOTES2.1 GENERAL SECTION 2 INSTALLATION AND DISASSEMBLYFigure 2-1Installation Components 2.2 TRANSCEIVER INSTALLATION2.3 POWER CABLE INSTALLATION Figure 2-2Mounting Bracket Installation2.2.2 INSTALLING MOUNTING BRACKET 2.2.3 INSTALLING MICROPHONE HANGERDB-9Pin Changing 20-AmperePower Cable Fuses2.4 USING AN EXTERNAL SPEAKER 2.5 ACCESSORY CABLE INSTALLATIONFigure 2-6Removing PC Board 2.6 TRANSCEIVER DISASSEMBLYFigure 2-5PC Board Screws Figure 2-4Cover and Front Panel Removal2.7 2-TONE/5-TONEMODULE INSTALLATION Figure 2-7 2/5-ToneModule InstallationSetting 5-ToneDeviation 25 kHz Channel Spacing - ±3.5 kHz 3.1 FEATURES SECTION 3 OPERATIONFigure 3-17600 Front Panel 3.3 BASIC OPERATION 3.2 CONTROLS AND DISPLAYDirect Selection - The F1-F4and 3.4 RECEIVING AND PLACING CALLS Key Label 3.5 PROGRAMMABLE FUNCTIONSTable 3-1Option Key Programmable Functions Function1.Press the TONE key and “TON--x”is displayed 3.6 CHANNEL SCAN 3.6.3 PRIORITY CHANNEL SAMPLING NovemberPart No. 4.1 GENERAL Figure 4-1Programming SetupSECTION PROGRAMMING4.2STARTING THE PROGRAM 4.3 SPECIAL KEYS AND FUNCTIONS4.4 MENU FLOW Current - Prints the currently displayed data Bank Select 4.4.7 SETUP MENUParameter DescriptionParameter Lockout Auto ResetParameter RF PWRDescription ParameterLabel Description LabelParameter Table 4-3DTMF Autodial Screen Description ParameterParameter Part No. Table 4-4Continuous Tone Screen DescriptionTable 4-5Scan Function Screen Description NovemberParameter Table 4-6 2-ToneCode Channel Screen DescriptionDescription ParameterBeep ParameterTable 4-7Common Screen Description Table 4-7Common Screen Description Continued Table 4-8Expert Screen DescriptionParameter Table 4-8Expert Screen Description Continued 4.5 UNIQUE PMR EUROPEAN SCREENSDescription PROGRAMMING Part No. Figure 4-2Memory Channel Screen PMR ModelsNovember 4-174-18 This page intentionally left blankNovember Part No.5.1 VHF RECEIVER CIRCUIT SECTION 5A VHF 7610 CIRCUIT DESCRIPTIONFigure 5-1Second IF System IC3 VHF 5.2 VHF TRANSMITTER CIRCUIT 5.3.1 PLL CIRCUIT Figure 5-3PLL Circuit VHF5.2.5 APC CIRCUIT 5.3 VHF PLL CIRCUITPort 5.4 VHF IC PIN DESCRIPTIONSLine DescriptionPort 5.5 UHF RECEIVER CIRCUIT SECTION 5B UHF 7640 CIRCUIT DESCRIPTIONFigure 5-4Second IF System IC1 UHF 5.6 UHF TRANSMITTER CIRCUIT 5.7 UHF PLL CIRCUIT Figure 5-6PLL Circuit UHFNovember 5.7.3 UHF POWER SUPPLY5.7.2 VCO CIRCUIT 5.7.4 UHF CPU IC1 PORT ALLOCATIONPart No. 5.7.5 UHF I/O EXPANDER IC12 MAIN UNIT5.7.6 UHF PORT EXPANDER IC13 MAIN UNIT November6.1 GENERAL SECTION 6 ADJUSTMENT PROCEDURETest Setup Figure6.1.3 TEST CABLE Figure 6-3Test Cable SchematicFigure 6-2Screen Display Example 6.1.2 TEST CHANNELSTable 6-1VHF Test Frequencies Table 6-2UHF Test FrequenciesADJUST /X /Y 6.3 PLL ADJUSTMENT VHF MODELS VHF ADJUSTMENTSVHF ADJUSTMENTS 6.2 PRELIMINARY SETUPFigure 6-4VHF Adjustment Points VHF ADJUSTMENTS CONT’DVHF ADJUSTMENTS CONT’D 6.5 RECEIVER ADJUSTMENTS VHF MODELSVHF ADJUSTMENTS CONT’D Figure 6-5Beep Tone Level AdjustmentUHF ADJUSTMENTS 6.6 PLL ADJUSTMENT UHF MODELS6.7TRANSMITTER ADJUSTMENTS UHF MODELS UHF ADJUSTMENTS CONT’D Figure 6-6UHF Adjustment Points6.7.4 DTCS WAVEFORM ADJUST UHF ADJUSTMENTS CONT’D 6.8 RECEIVER ADJUSTMENTS UHF MODELSHVFULSWLRQ SECTION 7 PARTS LISTæçìíýõ9+ôý0$,1ý81,7 7610 VHF Main UnitNovember 76105 VHF Main UnitHVFULSWLRQ HVFULSWLRQNovember 7610 VHF Main UnitHVFULSWLRQ HVFULSWLRQNovember Part No. 7610 VHF Main UnitHVFULSWLRQ HVFULSWLRQNovember 7610 VHF Main UnitHVFULSWLRQ HVFULSWLRQNovember 7610 VHF Main UnitHVFULSWLRQ HVFULSWLRQNovember 7610 VHF Main UnitHVFULSWLRQ HVFULSWLRQHVFULSWLRQ æçéíýõ8+ôý0$,1ý81,77640 UHF Main Unit 7610 VHF Main UnitNovember 7640 UHF Main UnitHVFULSWLRQ HVFULSWLRQNovember 7640 UHF Main UnitHVFULSWLRQ HVFULSWLRQNovember 7640 UHF Main UnitHVFULSWLRQ HVFULSWLRQHVFULSWLRQ 5HIý1Rï7640 UHF Main Unit HVFULSWLRQNovember 7640 UHF Main UnitHVFULSWLRQ HVFULSWLRQNovember Part No. 7640 UHF Main UnitHVFULSWLRQ HVFULSWLRQNovember 7640 UHF Main UnitHVFULSWLRQ HVFULSWLRQNovember Part No. 7640 UHF Main UnitHVFULSWLRQ HVFULSWLRQ7-17 7640 UHF Main UnitHVFULSWLRQ November5HIý1Rï 5217ý81,7 õ9+ý$1ý8+ý02/6ôFront Unit All Models 7640 UHF Main UnitNovember Front Unit All ModelsHVFULSWLRQ HVFULSWLRQFront Unit All Models æçìíýõ9+ôý&+$66,6ý3$576æçéíýõ8+ôý&+$66,6ý3$576 Chassis PartsPart No. VHF 7610 EXPLODED VIEW7-21 NovemberUHF 7640 EXPLODED VIEW ←FOLDOUT VHF Exploded ViewVHF 7610 BLOCK DIAGRAM MAIN UNITFRONT UNIT VHF 7610 Diode Basing Diagrams VHF 7610 Transistor Basing DiagramsVHF 7610 MAIN BOARD BOTTOM VIEW FOLDOUT →VHF 7610 MAIN BOARD TOP VIEW NovemberPart No. VHF MAIN UNIT VHF 7610 MAIN BOARD SCHEMATICUHF 7640 BLOCK DIAGRAM NovemberPart No. FOLDOUT → UHF 7640 MAIN BOARD BOTTOM VIEWNovember J5 T o O p t Ca ble UHF 7640 MAIN BOARD TOP VIEWJ4 T o O p tion al Un it J2 T o S p krUHF 7640 MAIN BOARD SCHEMATIC VHF/UHF FRONT UNIT BOARD BOTTOM VIEW VHF/UHF FRONT UNIT BOARD TOP VIEWFRONT UNIT VHF/UHF FRONT UNIT SCHEMATIC• DIODES UHF 7640 Transistor Basing DiagramsUHF 7640 Diode Basing Diagrams TRANSISTORS AND FETS