Kenwood NX-720H(G) Service Manual

Also see for Nexedge NX-720H: Instruction manual Instruction manual Instruction manual

Contents

NX-720H(G)/720H14CIRCUIT DESCRIPTION6. Control CircuitThe control circuit consists of the ASIC (IC507) and itsperipheral circuits. IC507 mainly performs the following:1) Switching between transmission and reception via thePTT signal input.2) Reading system, zone, frequency, and program data fromthe memory circuit.3) Sending frequency program data to the PLL.4) Controlling the squelch on/off using the DC voltage fromthe squelch circuit.5) Controlling the audio mute circuit using the decode datainput.6-1. ASICThe ASIC (IC507) is a 32bit RISC processor, equippedwith a peripheral function and ADC/DAC.This ASIC operates at 18.432MHz clock and 3.3V /1.5VDC. It controls the flash memory, SRAM, DSP, the receivecircuit, the transmitter circuit, the control circuit, and the dis-play circuit and transfers data to or from an external device.6-2. Memory CircuitThe memory circuit consists of the ASIC (IC507), theSRAM (IC503) and the flash memory (IC501). The flashmemory has a capacity of 32Mbit which contains the trans-ceiver control program for the ASIC and stores the data. Italso stores the data for the transceiver channels and operat-ing parameters that are written by the FPU. This programcan be easily written from external devices. The SRAM hasa capacity of 1Mbit which contains the work area and dataarea.Flash memoryNote : The flash memory stores the data that is written bythe FPU (KPG-141D), tuning data (Deviation, Squelch,etc.) and firmware program (User mode, Test mode, Tun-ing mode, etc.). This data must be rewritten when replac-ing the fl ash memory.SRAM (static memory)Note : The SRAM has a temporary data area and work area.6-3. Display UnitThe display unit is composed of the LCD driver IC (IC1),the LCD & Key backlight, etc.T h e L C D i s c o n t r o l l e d u s i n g t h e 4 s e r i a l l i n e s(LCDDI,LCDCE,LCDCL,LCDDO) from the ASIC (IC507).6-4. Key Detection CircuitThe keys are detected using an LCD driver IC (IC1). If apressed key is detected by IC1, the information is passed toIC507 through the serial line.6-5. DSPThe DSP circuit consists of a DSP (IC502) and processes the baseband signal. The DSP operates on an external clock of 18.432MHz(the same as the IC507), the I/O section operates at 3.3V and thecore section operates at 1.5V. The DSP carries out the followingprocesses:• 4 level FSK processing• Analog FM pre-emphasis/de-emphasis• Vocoder processing between the audio codec and modulation/de-modulation• CAI processing, such as error correction encoding• QT/DQT encoding/decoding• DTMF encoding/decoding• MSK encoding/decoding• 2-tone encoding/decoding• Compressor/expander processing• Voice scrambler processing• Transmit/receive audio fi ltering processing• Microphone amplifi er AGC processing• Audio mute processing• Modulation level processing7. Power Supply Circuit+B is connected to the Final amplifier and the DC/DCconverter IC (IC405). IC405 regulates the +B voltage to 5.0V(50M). 50M operates whenever +B is supplied. IC401 (33M)and IC408 (15M) are enabled while the 50M is operating.33M and 15M provide the power to the ASIC (IC507),DSP (IC502), and Flash memory. At this time the ASICstarts working. The voltage detector IC (IC402) watches the+B voltage. If the +B voltage is higher than 8.6V, IC402 (/BINT) outputs High. If the /BINT signal is high, Q403 (SBSW) is turned on by the SBC signal from the ASIC. (High :SBC=ON, Low : SBC=OFF). When the SB is turned on, IC1(80C), IC404 (50C), Q402 (80ANT), Q404 (80T), Q415, 416(150C), Q417 (50R) and Q408 (50CS) start working. IC409,Q409 and Q410 are controlled by the SBC signal. If theSBC signal becomes High, IC409 (33C) operates, and Q409(33A_2) and Q410 (50MC SW) turn on.The ASIC sets the TXC signal to High during transmis-sion to the supply power (80T) for the transmission circuit.The ASIC sets the signals (RXC) to High during reception tothe supply power (50R) for the reception circuit.When the ASIC detects the PSW (Power switch) signal,IGN (Ignition sense) signal or /BINT signal, it sets the SBCsignal to Low, and turns the transceiver power (SB) off.When D401 and Q401 detect an over-voltage condition, theyturn Q403 (SB SW) off, but the ASIC continues to function.