Kenwood NX-300S Service Manual

Also see for NEXEDGE NX-300: Brochure Instruction manual Instruction manual Instruction manual Instruction manual

NX-300(S)156-2. Memory CircuitThe memory circuit consists of the ASIC (IC108) and theSRAM (IC103) and flash memory (IC101). 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 capacity of 1M-bit thatcontains work area and data area.■ Flash memoryNote: The flash memory stores the data that is written bythe FPU (KPG-111D), tuning data (Deviation, Squelch,etc.) ,and firmware program (User mode, Test mode, Tuningmode, etc.). This data must be rewritten when replacing thefl ash memory.■ SRAM (Static memory)Note: The SRAM has temporary data area and work area.When the power supply is off, it is backed up by an internalsecondary lithium battery. Therefore, the saved data is notlost.6-3. Key Detection CircuitKeys are detected using the key scan circuit in IC108.The /KEYI* signals that are normally pulled down go highwhen any key is pressed.6-4. Low Battery WarningThe battery voltage is divided using R444 and R445 andis detected by the ASIC (IC108). When the battery voltagefalls below the voltage set by the Low battery warning ad-justment, the red LED blinks to notify the operator that it istime to replace the battery. If the battery voltage falls evenmore (approx. 5.8V), a beep sounds and transmission stops.Low battery warning Battery conditionThe red LED blinks duringtransmission.The battery voltage is low butthe transceiver is still usable.The red LED blinks and thewarning tone beeps while thePTT switch is pressed.The battery voltage is low andthe transceiver is not usable tomake calls.6-5. DSPThe DSP circuit consists of a DSP (IC102) and process-es the baseband signal. The DSP operates on an externalclock of 18.432MHz (the same as the IC108), the I/O sectionoperates at 3.3V and the core section operates at 1.5V. TheDSP carries 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• 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 CircuitThe battery voltage (+B) is provided from the battery ter-minal on the TX/RX unit (X57). The battery voltage passesthrough the 2.5A fuse (F900), and goes to the RF fi nal am-plifi er, AVR ICs (IC902, IC903), and Control unit (X53-443).In the control unit, +B is connected to the DC/DC (IC407),AVR ICs (IC411, IC708, IC416), and voltage detector IC(IC414). The voltage detector watches the battery voltage.If the battery voltage is 5.6V or higher, the detector outputsHigh. While the output of IC414 is High, IC416 and Q409provide 3.1V (31BU) to the backup-section.When the VOL SW is turned on, SB1 becomes high (bat-tery voltage). The DC/DC (IC407) operates if both SB1 andthe output of the detector are high. IC407 outputs 3.8V and itactivates IC404 (33M), IC717 (15M), and IC406 (33A). As aresult, the ASIC and DSP operate.The SBC signal becomes High after the ASIC operates,IC708 (5A), Q403 on the Control unit (SB2) and Q901 on theTX-RX unit (SB3) are turned on. IC901 and IC903 operateby turning on these AVR ICs and FET switches.The 5UC signal becomes High when an option is in-stalled on the universal connector. Then IC411 (50U) oper-ates.When the /SAVE signal becomes High, IC902 (50C)operates. The output of IC902 is connected to three FETswitches (Q902, Q903, Q905). When the SBC signal be-comes High, IC903 (33C) operates. The FET switches arecontrolled by the CPU. Q905 (50T) is turned on in transmitmode. Q902 (50R) and Q903 (50IF) are turned on in receivemode.When the VOL SW is turned off the /PSW signal be-comes Low. After detecting the /PSW signal, the ASICchanges SBC signal to Low. Then the power supplies exceptIC416 (31BU) stop.CIRCUIT DESCRIPTION