EFJohnson 7780 service manual Control Logic and Display, Receive Audio Processing

Page 69

CIRCUIT DESCRIPTION

4.4.3 POWER CONTROL (IC2A/B)

The power output circuit maintains a steady power output level by controlling the supply voltage to the first stage in power module IC1 (VCC1). The output power is monitored using a directional coupler consisting of L34, L13, C33, C35, D4, D5, and several other components. Reflected (reverse) power is detected by L13/D5, and forward power is detected by L12/D4. These couplers produce a DC voltage that is proportional to the reverse or forward power.

The forward power signal is amplified by IC2A and is combined with the reverse power signal on pin 6 of IC2B. If there is no reverse power being detected, IC2B amplifies only the difference between the forward power signal on pin 6 and the reference voltage on pin 5. This reference voltage controls the power output, and it is set by the control logic through potentiometer 2 in IC209 in the logic unit.

As forward or reverse power increases, the output voltage on pin 7 decreases. Q5 and Q6 then turn off more which decreases the supply voltage applied to VCC1 of IC1. Power then decreases to maintain a stable output. The opposite occurs if forward or reverse power decrease. The power decrease resulting from an increase in reverse power prevents transmitter damage which may result if excessive power is reflected back into the transmitter. This may occur, for example, if the transmitter is keyed with a defective antenna.

4.5 CONTROL LOGIC AND DISPLAY

NOTE: A block diagram of the RF and logic units is located on page 8-3.

4.5.1 CONTROL LOGIC

The digital control logic is based on 8-bit CMOS microprocessor IC306. The operating speed is set by 9.8304 MHz crystal X2. A clock shift signal applied through D301. This signal goes high to shift the clock frequency slightly when the second harmonic inter- feres with the receive signal.

A serial data bus formed by MSI, MSO, and MSCK (pins 49-51) is used to transfer data to and

from two external devices. They are 16K x 8 EEPROM IC304 and DTMF encoder IC303. Another serial port formed by XTXD and XRXD is used to transfer programming data to and from an external computer. This port is fed out of the transceiver on pins 6 and 7 of the accessory connector. Descriptions of the IC306 pins are located in Table 4-1.

4.5.2 DISPLAY ASSEMBLY DESCRIPTION

IC1 on the display board is an intelligent LCD display controller/driver. It communicates with the microprocessor on the logic board over a serial bus consisting of MSCK (serial clock) and MSO (serial data), and DISST (display strobe) signals. IC1 is set for 1/3 bias and 1/5 duty cycle and drives an 8-char- acter, 14-segment display at a 98 Hz frame frequency. The LCD display (DS6) has 127 segments that are driven by a 34-segment signal with 4 common lines.

4.6 RECEIVE AUDIO PROCESSING

4.6.1 BANDPASS FILTER (IC101)

The receive audio and data signal from the IF module in the RF unit is called DET. It is applied to IC101 in the receive audio circuit, IC102 in the receive data circuit, and IC110 in the SMARTNET data circuit. The receive audio circuit operates as follows, and the other circuits are described in later sections.

The DET signal is applied to IC101 which is a bandpass filter which passes frequencies from 300- 3000 Hz. This attenuates Call Guard (CTCSS/DCS) signaling and high-frequency harmonics. This filter also provides de-emphasis of the audio signal.

On the input of IC101, pin 1 of Q110 is low in the wideband mode and high in the narrow band mode. Therefore, R102 is grounded in the wideband mode to lower the input level to IC101. This maintains a constant audio output level since the higher deviation in the wideband mode results in a higher input level. Also on the input of IC101, the NPSPAC line control- ling Q111 is high when a NPSPAC channel is selected and low at other times. This grounds R167 in the NPSPAC mode to lower the input level since NPSPAC channel deviation is higher than narrow band deviation.

 

November 1999

4-5

Part No. 001-7780-500

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Contents 7780 Page Page Table of Contents Table of Contents CONT’D List of Figures List of TablesScope of Manual Equipment Description General InformationFactory Customer Service AccessoriesPart Number Breakdown Transceiver IdentificationAccessory AccessoriesToll-Free 800 Factory ReturnsReplacement Parts Internet Home Intrinsically Safe InformationDefinitions Possible Ignition Sources Temperature Code T3CIntrinsically Safe and Nonincendive Ratings Classification of Hazardous Areas and AtmospheresMaterial Classification Accessing PC BoardsTypical Hazard Group Class Area ClassificationRemoving Logic Unit Removing RF UnitGeneral SpecificationsFeatures Transceiver OperationControls and Display Low-Battery Indicator Amber TX Indicator Red Indicates when the transmitter is keyedDisplay Front Panel Keys Full Keypad ModelDisplay Option Switches Turning Power on and Setting VolumeGeneral Operation BacklightOption Switch Functions Function ConvSee Scanning Tone ENABLE/DISABLEConventional and SMARTNET/ Smartzone Operation Conventional Features Display Mode SelectionMonitoring Before Transmitting Monitor Mode Busy Channel LockoutCall Guard Squelch Conversation Timer Penalty TimerPower Output Select Conventional Mode ScanningPriority Channel Sampling Standard Conventional Calls DTMF/ANI SignalingViewing Unit ID SMARTNET/SMARTZONE FeaturesStandard Group Calls Enhanced Private Conversation CallsTransceiver Operation Private Conversation II Calls Telephone Calls Call Alert Emergency Alarm and Call MessagingSending Status Conditions Failsoft Operation SMARTNET/SMARTZONE ScanningDynamic Regrouping Supervisory Tones Keypad Programming Menu DescriptionZone Change Parameter Channel Change Parameter System ParametersChannel Parameters Pctrunk Software Installation Programming SetupTransceiver Programming Computer DescriptionStarting and Exiting Connecting RPI to Computer and TransceiverProgramming File Types Help FilesProgramming Procedure Screen Pop-Up Buttons and File Size IndicatorFile Size Indication Creating and Displaying SystemsMenu Bar Menu CommandsDownload Menu Upload Menu Radio Type MenuSystems Menu Window MenuRADIO-WIDE Parameter Screens DefaultsBand ZonesRadio-Wide Scan List Screen Radio Wide Scan ListModify List Screen Assign Function ButtonsRADIO-WIDE SMARTNET/SMARTZONE Screen RADIO-WIDE Conventional ScreenFull Spectrum CC Scan Hot DtmfRADIO-WIDE Portable Options Screen Adjustable ParametersProgramming Conventional Systems and Channels Conventional System General ScreenConventional System Modify Scan List Screen TimersKeypad Editing Scan List ButtonScan Timers Setting UP Conventional ChannelsPriority Channel Selection Selected Channel Conventional Channel Screen ParametersSignaling Transmit PowerChannel Type Tx Time-OutTime-Out Timer Restricted AccessISW Delay Time Splinter ChannelsSMARTNET/SMARTZONE System Phone Interconnect Screen SMARTNET/SMARTZONE System Other ID’S ScreenPhone Interconnect Private CallEmergency Alarm SMARTNET/SMARTZONE System Emergency Settings ScreenSMARTNET/SMARTZONE System Talk Groups Screen Failsoft ChannelSMARTNET/SMARTZONE System Lists Screens Trunking Phone List ScreenMessage Aliasing Screen Control Channels Screen Announcement Groups ScreenTrunking Call List Screen Setting UP SMARTNET/SMART- Zone Channels Status Aliasing ScreenSMARTNET/SMARTZONE Channel Screen Parameters Other Screen Parameters SMARTNET/SmartZone Channel ScreenRecommended Tone Call Guard Codes Freq Call Guard CTCSS/DCS Codes and TonesMHz Channels MHz Channels MHz Channels MHz Channels MHz Channels MHz Channels Power Switching Power Switching and RegulationCircuit Description Synthesizer DescriptionVCO and Tcxo Modulation Synthesizer Chip IC1Charge Pump Q1, Q2, Loop Filter Receiver Circuit Description RF Amplifier Q1, First Mixer Q2If Amplifier Q2, LIMITER/DETECTOR IC3 Squelch Circuit IC4A/B, IC5A Antenna Switch and LOW-PASS FilterTransmitter Description Amplifier Q9, Driver Q8Receive Audio Processing Control Logic and DisplayPin Port Name Input or Description Active High Output Microprocessor IC306 Pin DescriptionsHvfulswlrq Audio Amplifier IC104-IC106 Receive and Transmit Data ProcessingReceive Data FILTER/DETECTOR IC102A/B, IC107A/B Transmit Audio Processing Transmit Data Filter IC206B/ IC206ASmartnet Data Processing LOW-PASS Filter IC205A/BBattery Pack Battery Pack and Charger InformationPower Setting Operating Time Function Fahrenheit CelsiusBattery Pack and Charger Information Test Setup Alignment Procedure and Performance TestsMm/3/32 Mm/1/8 Phone Jack Tune Software HqhudoMain Pctune Screen Preliminary SetupTransmit Power Adjustment Screen Transmit Frequency and PowerHigh Power Level = 3.0 watts Low Power Level = 1.0 watt Modulation BalanceRssi Adjust Squelch AdjustAudio Deviation Data DeviationReceiver Performance Tests Performance TestsTransmitter Performance Tests Power OutputTransmit Frequency Transmit ModulationThis page intentionally left blank Display Assembly Parts ListChassis Parts Ref No DescriptionDisplay Assembly KEY AssemblyIf Assembly KEY AssemblyIf Assembly RF Unit PLL AssemblyRF Unit NJM2904V-TE1 IC RF Unit Logic Unit Logic Unit TDA7233D IC Logic Unit 200K ERJ3GE MP35 MP18 MP25 EP2 KEY Front PanelEP1 MP32 MP33 MP27 MP34 MP28 MP29 MP23 MP22 MP30 MP24 MP26 MP18 Schematic Diagrams and Component Layouts PLL Board TOP ViewPLL Board Bottom View If Board Bottom View If Board TOP ViewRF Unit Transceiver Block DiagramMIC RF Board TOP ViewIf AMP RF Board SchematicHD1 Logic Board TOP ViewReceive Audio Processing Logic Board SchematicGND KEYR3 KEYR2 KEYR1 KEYR0 KEYS3 KEYS2 KEYS1 KEYS0 GND Display Board Bottom ViewDS3 DS4 DS5 Display Board SchematicKEY Board Back View KEY Board Front ViewS S R R R R KEY Board SchematicScan HC2 HC7 HC8 HC3 Schematic Diagrams and Component Layouts
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