Kenwood TKR-850 Service Manual

Also see for TKR-850: Brochure & specs Function reference Instruction manual Instruction manual Programming reference

23TKR-8505-6. DSPThe DSP circuit filters transmit/receive audio signal andencode/decodes signaling (QT, DQT). This circuit consistsof IC618, IC612, IC613, IC614, IC603, IC606, IC608, IC610,IC616, and IC619.The receive signal DET is converted from analog to digitalby IC614 with a sampling frequency of 16.128kHz. The digi-tized audio signal is sent to DSP IC618 to process the signal-ing signal and audio signal. The processed digital audio sig-nal is fed to CODEC IC613, converted from digital to analog,and the analog signal is output from pin 16 (AOUTR). Then,the audio signal is amplified by IC619 (B/2), passes throughthe IC619 (A/2) low-pass filter, and goes to an electronic vol-ume IC615.The transmit audio signal coming from IC605 is amplifiedby IC610, fed to pin 3 (AINL) of CODEC IC614, and con-verted from analog to digital at a sampling frequency of16.128kHz. The digitized transmit audio signal is AGC-pro-cessed, pre-emphasized and filtered at 300Hz to 3kHz byDSP IC618, and the resulting signal is fed back to CODECIC614, and converted from digital to analog, and the analogsignal is output from pin 15 (AOUTL). The transmit signalfrom AOUTL is amplified by IC616 (B/2), passes through theIC616 (A/2) low-pass filter, and goes to the IC611 (A/2) sum-ming amplifier.IC613 is a counter IC and the clock required for theCODEC and DSP is generated by dividing the 16.515MHzclock signal produced by DSP IC618.IC603 and IC606 are interface IC between the CPU oper-ated at 5.0V and the DSP operated at 3.3V.5-7. Base-Band CircuitThe base-band circuit switches between the modulationsignal to the transmitter circuit, and remote audio and ad-justs their levels. This circuit consists of IC605, IC607,IC611, IC615, and IC617.Modulation inputs include local microphone input, low-speed data (LSD), high-speed data (HSD), external audio in-put (TA), and external data input (TD), and demodulation out-puts include receive audio output (RA), and receive data out-put (RD).The multiplexer (IC605) changes signals, the electronicvolume (IC615) adjusts the level, and the operational ampli-fier (IC607, IC611, IC617) amplifiers and sums signals.5-8. RS-232C CircuitThe RS-232C circuit connects the RS-232C serial port of apersonal computer directly to this model to perform FPUoperation. The FPU operation can also be performed by con-necting a programming cable (KPG-46) to the local micro-phone on the front panel. But, if the D-sub connector on therear panel is used, the programming cable is not required.The 232C driver IC (IC620) changes the TTL-232C level. Thefirmware can only be rewritten with the local microphone onthe front panel.5-9. Power Supply CircuitThe power supply circuit generates power to operate theCPU, DSP, flash ROM, bi-directional buffer, and base-bandcircuit. This circuit consists of IC624, IC625, IC626, IC627,IC628, and IC630.6. DC Power Supply Circuit6-1. DC Source Switching Relay Circuit1. The final unit contains a relay (K1) for switching betweenthe Main DC and Backup Battery.If an external power source is connected to the Main DCterminal, the Backup terminal is isolated by the relay. Ifthe Main DC turns OFF due to power failure, it isswitched to the Backup terminal by the relay.The CPU monitors which is used, Main DC or BackupBattery.2. Trickle charge circuitIf both Main DC and Backup Battery are connected,trickle charging of 0.5 A max. can be performed from theMain DC power supply to the Battery.(The default is OFF. See the Modification section for in-formation on the modification method.)The battery is charged from the Main DC with D8, D9 andR61. If it exceeds 0.5 A, the charging circuit is turnedOFF by D9.6-2. SB Switching Relay Circuit1. SB (Switched +B) is supplied through the relay (K1) in theTX-RX unit A/2.When S507 (DC source switch) in the display unit isturned ON, the relay (K1) is turned ON to output SB.2. If +B exceeds 18V, the relay is forcibly turned OFF byD12 and Q25 to interrupt the power and protect the mainunit.D8D9R61LandMainDCBackupbattery120mA+BK1(Relay)Final unit (A/2)TX-RX unit (A/2)TX-RX unit (B/2)R54IC604CPUBUP 16Q601+BR165 R166D12K1Q24Q25SBLand(PSW)Display unit(Front panel)S507Fig. 9 DC source switching relay circuitFig. 10 SB switching relay circuitCIRCUIT DESCRIPTION