Manuals / EFJohnson / Home Audio / Speaker

EFJohnson 761X, 764X service manual 1Second IF System IC3 VHF

Models: 761X 764X

1 99

Download 99 pages 7.65 Kb

Page 45

Figure 5-1 Second IF System IC3 (VHF)

VHF (7610) CIRCUIT DESCRIPTION

Figure 5-1 Second IF System IC3 (VHF)

Figure 5-2 Audio Switching and Amplifier Circuit (VHF)

are part of the quadrature detector. The audio signal is fed out on pin 9 (IC3) and applied to the AF amplifier circuit.

5.1.5 AUDIO AMPLIFIER CIRCUIT

The AF (audio frequency) amplifier circuit pro- vides drive to the speaker (a block diagram is shown in Figure 5-2). The audio signal from IC3, pin 9 is applied to AF amplifier IC7A and then fed to pin 1 of AF switching circuit IC4. The switched output signal on IC4, pin 2 is then applied to high-pass filter IC8A/ B. 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 IC8, pin 7 is applied to limiter IC7b and buffer IC7c. De-emphasis is pro-

vided by R145 and C182. The audio signal is then applied to pin 16 of level controller IC5. This device allows the CPU to control the speaker volume level. The level controlled signal is fed out of IC5 on pin 15 and applied to low-pass filter IC6b. It is then applied to AF switching circuit IC4 on pin 8, and the switched output is on pin 9. This signal is buffered by IC6d and then amplified by AF amplifier IC10 to provide drive to the speaker.

5.1.6 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	5A-2

Image 45

EFJohnson 761X, 764X service manual 1Second IF System IC3 VHF

Contents

VHF 146-174MHz 45 Watts Part No. 761x VHF 764x UHF Conventional MobileUHF 400-430, 450-470, 490-512MHz 35 Watts Part No.UHF 400-430, 450-470, 470-490,or 490-512MHz VHF 146-174MHz 45 Watts35 Watts 761x VHF 764x UHF CONVENTIONAL FM TWO-WAYRADIO2 INSTALLATION AND DISASSEMBLY TABLE OF CONTENTS1 GENERAL INFORMATION 3 OPERATION6 ADJUSTMENT PROCEDURE TABLE OF CONTENTS CONT’D7 PARTS LIST 5A VHF 7610 CIRCUIT DESCRIPTIONLIST OF TABLES 8SCHEMATIC DIAGRAMS AND COMPONENT LAYOUTSLIST OF FIGURES TABLE OF CONTENTS CONT’D1.6 ACCESSORIES 1.3 PRODUCT WARRANTY1.7 FACTORY CUSTOMER SERVICE SECTION 1 GENERAL INFORMATION1.8 FACTORY RETURNS Table 1-175xx AccessoriesAccessory Toll-Free:8001.10 INTERNET HOME PAGE 1.9 REPLACEMENT PARTSThis page intentionally left blank NovemberPart No. GENERAL 7610 VHF AND 7640 UHF MOBILE SPECIFICATIONSNovember NOTESFigure 2-1Installation Components SECTION 2 INSTALLATION AND DISASSEMBLY2.2 TRANSCEIVER INSTALLATION 2.1 GENERAL2.2.2 INSTALLING MOUNTING BRACKET Figure 2-2Mounting Bracket Installation2.2.3 INSTALLING MICROPHONE HANGER 2.3 POWER CABLE INSTALLATION2.4 USING AN EXTERNAL SPEAKER Changing 20-AmperePower Cable Fuses2.5 ACCESSORY CABLE INSTALLATION DB-9PinFigure 2-5PC Board Screws 2.6 TRANSCEIVER DISASSEMBLYFigure 2-4Cover and Front Panel Removal Figure 2-6Removing PC Board2.7 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 Table 3-1Option Key Programmable Functions 3.5 PROGRAMMABLE FUNCTIONSFunction Key Label1.Press the TONE key and “TON--x”is displayed 3.6 CHANNEL SCAN 3.6.3 PRIORITY CHANNEL SAMPLING NovemberPart No. SECTION Figure 4-1Programming SetupPROGRAMMING 4.1 GENERAL4.2STARTING THE PROGRAM 4.3 SPECIAL KEYS AND FUNCTIONS4.4 MENU FLOW Current - Prints the currently displayed data Parameter 4.4.7 SETUP MENUDescription Bank SelectParameter Parameter Auto ResetRF PWR LockoutDescription ParameterLabel Description LabelParameter Table 4-3DTMF Autodial Screen Description ParameterParameter Table 4-5Scan Function Screen Description Table 4-4Continuous Tone Screen DescriptionNovember Part No.Description Table 4-6 2-ToneCode Channel Screen DescriptionParameter 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 November Figure 4-2Memory Channel Screen PMR Models4-17 Part No.November This page intentionally left blankPart No. 4-185.1 VHF RECEIVER CIRCUIT SECTION 5A VHF 7610 CIRCUIT DESCRIPTIONFigure 5-1Second IF System IC3 VHF 5.2 VHF TRANSMITTER CIRCUIT 5.2.5 APC CIRCUIT Figure 5-3PLL Circuit VHF5.3 VHF PLL CIRCUIT 5.3.1 PLL CIRCUITLine 5.4 VHF IC PIN DESCRIPTIONSDescription PortPort 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 UHF5.7.2 VCO CIRCUIT 5.7.3 UHF POWER SUPPLY5.7.4 UHF CPU IC1 PORT ALLOCATION November5.7.6 UHF PORT EXPANDER IC13 MAIN UNIT 5.7.5 UHF I/O EXPANDER IC12 MAIN UNITNovember Part No.Test Setup SECTION 6 ADJUSTMENT PROCEDUREFigure 6.1 GENERALFigure 6-2Screen Display Example Figure 6-3Test Cable Schematic6.1.2 TEST CHANNELS 6.1.3 TEST CABLETable 6-1VHF Test Frequencies Table 6-2UHF Test FrequenciesADJUST /X /Y VHF ADJUSTMENTS VHF ADJUSTMENTS6.2 PRELIMINARY SETUP 6.3 PLL ADJUSTMENT VHF MODELSFigure 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 MODELSæçìíýõ9+ôý0$,1ý81,7 SECTION 7 PARTS LIST7610 VHF Main Unit HVFULSWLRQHVFULSWLRQ 76105 VHF Main UnitHVFULSWLRQ NovemberHVFULSWLRQ 7610 VHF Main UnitHVFULSWLRQ NovemberHVFULSWLRQ 7610 VHF Main UnitHVFULSWLRQ November Part No.HVFULSWLRQ 7610 VHF Main UnitHVFULSWLRQ NovemberHVFULSWLRQ 7610 VHF Main UnitHVFULSWLRQ NovemberHVFULSWLRQ 7610 VHF Main UnitHVFULSWLRQ November7640 UHF Main Unit æçéíýõ8+ôý0$,1ý81,77610 VHF Main Unit HVFULSWLRQHVFULSWLRQ 7640 UHF Main UnitHVFULSWLRQ NovemberHVFULSWLRQ 7640 UHF Main UnitHVFULSWLRQ NovemberHVFULSWLRQ 7640 UHF Main UnitHVFULSWLRQ November7640 UHF Main Unit 5HIý1RïHVFULSWLRQ HVFULSWLRQHVFULSWLRQ 7640 UHF Main UnitHVFULSWLRQ NovemberHVFULSWLRQ 7640 UHF Main UnitHVFULSWLRQ November Part No.HVFULSWLRQ 7640 UHF Main UnitHVFULSWLRQ NovemberHVFULSWLRQ 7640 UHF Main UnitHVFULSWLRQ November Part No.HVFULSWLRQ 7640 UHF Main UnitNovember 7-17Front Unit All Models 5217ý81,7 õ9+ý$1ý8+ý02/6ô7640 UHF Main Unit 5HIý1RïHVFULSWLRQ Front Unit All ModelsHVFULSWLRQ Novemberæçéíýõ8+ôý&+$66,6ý3$576 æçìíýõ9+ôý&+$66,6ý3$576Chassis Parts Front Unit All Models7-21 VHF 7610 EXPLODED VIEWNovember Part No.UHF 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 J4 T o O p tion al Un it UHF 7640 MAIN BOARD TOP VIEWJ2 T o S p kr J5 T o O p t Ca bleUHF 7640 MAIN BOARD SCHEMATIC VHF/UHF FRONT UNIT BOARD BOTTOM VIEW VHF/UHF FRONT UNIT BOARD TOP VIEWFRONT UNIT VHF/UHF FRONT UNIT SCHEMATICUHF 7640 Diode Basing Diagrams UHF 7640 Transistor Basing DiagramsTRANSISTORS AND FETS • DIODES