Kenwood TK-80 Service Manual
Also see for TK-80: Service manual
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Contents
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TK-80164-2. Power control circuitPower is controlled by lowering the base voltage of Q61 inthe TX-RX unit. As the base voltage of Q61 decreases, theemitter voltage of Q60 and Q61 decreases. This activatesALC and reduces the power even if the base voltage (VSF) ofQ60 is low. The power change is shifted by D/A converterIC13 for changing base voltage of Q61 (Fig. 7).4-3. Protection circuitWhen the reflected wave voltage (VSR) detected by thefilter unit rises, Q63 in TX-RX unit turns on to reduce the volt-age of the ALC time constant line. The drive is decreasedand the power is reduced to protect the final transistor.8F+Q64Q60 Q61Q62Q65D69D68D67D71D72VR14 +++VSFVSRExt ALCD70+Q63VR12ALC out–6VTXBQ69Q67 Q68AMBIC13D/A3POCFig. 7 ALC and power control circuits5. Digital Control CircuitThe TK-80’s digital control circuit comprises a 16-bit micro-computer CPU IC5, a reset IC3, an EEPROM IC6. Expander I/O IC7 since there are many control signals for TX-RX unit andfilter unit, they are output to the shift register (serial to parallelconverter) in series (Fig. 8).5-1. Power switchWith this transceiver, the power is turned on and off bythe microcomputer. When the power switch is pressed, themicrocomputer detects it and energizes, the power relay tosupply 14V to the transceiver. When the power switch ispressed to turn the transceiver off, the microcomputerchecks it a little longer than when turning the power on andde-energizes the power relay.CIRCUIT DESCRIPTION4-4. Temperature protectionIf the final heat sink temperature rises, Q9 in the final unitturns on and the fan starts running at low speed and duringtransmission Q10 turns on and starts running a high speed ifthe final heat sink temperature rises further.If this is not enough to prevent the temperature from con-tinuing to rise, the control unit CPU IC5 temperature detec-tion port THP becomes “H”, forcibly lowering the RF output.Also, if there are any fan troubles or if something happens toget entangled and prevents the fan from turning, the RF out-put is similarly forced down to prevent overheating. |
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