Kenwood NX-900 Service Manual

Also see for NEXEDGE NX-900: Function reference Instruction manual Instruction manual

NX-900216. Control CircuitThe control circuit consists of the ASIC (IC510) and itsperipheral circuits. IC510 mainly performs the following;1) Switching between transmission and reception by PTTsignal input.2) Reading system, zone, frequency, and program datafrom the memory circuit.3) Sending frequency program data to the PLL.4) Controlling squelch on/off by the DC voltage from thesquelch circuit.5) Controlling the audio mute circuit through decode datainput.6-1. ASICThe ASIC (IC510) is a 32-bit RISC processor, equippedwith peripheral function and ADC/DAC.This ASIC operates at a 18.432MHz clock and 3.3V /1.5VDC. It controls the flash memory, SRAM, DSP, receive cir-cuit, transmit circuit, control circuit, and display circuit andtransfers data to or from an external device.6-2. Memory CircuitMemory circuit consists of the ASIC (IC510) and SRAM(IC503), and the flash memory (IC501). The flash memoryhas capacity of 32M-bit that contains the transceiver controlprogram for the ASIC and stores the data. It also stores thedata for transceiver channels and operating parameter thatare written by the FPU. This program can be easily writtenfrom external devices. The SRAM has a capacity of 1M-bitthat contains the work area and data area.■ Flash memoryNote: The flash memory stores the data that is writtenby the FPU (KPG-111D), tuning data (Deviation, Squelch,etc.), and firmware program (User mode, Test mode, Tuningmode, etc.). This data must be rewritten when replacing theflash memory.■ SRAM (Static memory)Note: The SRAM a has temporary data area and workarea.When the power supply is off, it is backed up by an inter-nal secondary lithium battery. Therefore, the save data doesnot break.■ Real-time clockThe clock function is based on a real-time clock IC (IC504).When the power supply is off, it is backed up by an internalsecondary lithium battery.6-3. Display UnitThe display unit is composed of the MCU (IC911) andthe memory IC (IC913), and the LCD & Key backlight, etc.The LCD Ass’y (with LCD Driver) is controlled using thebus lines on the connector (CN905) of the display unit. Itcorrects the LCD contrast voltage using IC909.6-4. Key Detection CircuitKeys are detected using the Key scan circuit in IC911.The /KI* and KO* signals that are normally pulled up go lowwhen a key is pressed.6-5. DSPThe DSP circuit consists of a DSP (IC717) and processesthe baseband signal. The DSP operates on an external clockof 18.432MHz (the same as IC510), the I/O section operatesat 3.3V and the core section operates at 1.5V. The DSP car-ries out the following processes:• 4 Level FSK processing• Analog FM pre-emphasis/de-emphasis• Vocoder processing between audio codec and modula-tion/demodulation• CAI processing, such as error correction encoding• QT/DQT encoding/decoding• LTR encoding/decoding• DTMF encoding/decoding• MSK encoding/decoding• Compressor/expander processing• Voice scrambler processing• Transmit/receive audio filtering processing• Microphone amplifier 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 to5.0V (50M). 50M operates whenever +B is supplied. IC402(33M), IC408 (33A) and IC409 (15M) are enabled while 50Mis operating. Q412 is controlled by the SBC_2 signal. If theSBC_2 signal becomes High, it operates and Q416 (33A2SW) is turned on. Q412 is controlled by the SBC_2 or 33Msignal via D408. If the SBC_2 or 33M signal becomes High,it operates and Q412 (50MC SW) is turned on.33M and 15M provide the power to the ASIC, DSP,and Flash memory. At this time the ASIC starts working.The voltage detector IC (IC401) watches the +B voltage. Ifthe +B voltage is higher than 8.6V, IC401 (/BINT) outputsHigh. If the /BINT signal is high, Q404 (SB SW) is turned onby the SBC_2 signal from the ASIC. (High : SB=ON, Low: SB=OFF). When the SB is turned on, IC403 (80C), IC404(50C), IC406 (33C) and IC407 (33GPS) start working.The ASIC sets the TXC signal to High during transmis-sion to supply power (80T) to the transmission circuit. TheASIC sets the RXC signal to High during reception to supplypower (80R, 50R) to 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,they turns Q404 (SB SW) off, but the ASIC continues towork.CIRCUIT DESCRIPTION