Alinco DX-70, Руководство по обслуживанию

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c. Fan Control
The heat of Q606 and Q607 is detected by the thermistor TH601, and the fan is
controlled. While transmitting, the resistance value is decreased by the rising of
the temperature, then the voltage of inverting input terminal of IC601A/B is de­
creased. Non-inverting input is applied with the voltage corresponding to the
temperature. When the temperature goes up to about 50°C or more and the
compared voltage becomes lower than the inverting input voltage, Q607 is turned
ON by the output voltage of comparator, 10601: A. Then the fan starts turning at a
low speed by the value of series resistor (R639).
When the temperature rises more and the voltage becom es much lower than the
compared voltage IC6Q1: B, Q608 is turned ON. Then R639 is turned O FF and
the fan turns at a high speed according to the value of series resistor of R640 to
decrease the compared voltage of IC601: A.
When the temperature goes up to about 100°C and the voltage is decreased
further lower, IC601: A supplies again, then R639 and R640 are connected in
parallel to turn the fan at a higher speed. Although ordinary PDWN is pulled up to
14V by R637, the power output is set to LOW because both cathode terminals of
D608 become LOW when the fan turns at a high speed. Then the signal is sent to
the main unit as the control signal for power down at high temperature.
As the compared voltage of IC601: B is decreased in D611 while receiving,
IC601:B does not work if the temperature does not go up higher than it while
transmitting. The temperature, at which the fan turns at a middle speed or more, is
higher than it while transmitting. At high temperature, fan's turning speed comes
down whiie receiving.
d. Protection Circuit
For the protection of the final power amplifier, the followings are equipped:
SW R detection
Protection against over current
Power down circuit for the temperature detection
e. CW Keying Circuit
As the base voltage of main unit 049 goes down to LOW by CW keying, the
voltage is supplied to collector. This output controls all of the circuit operation by
CW keying.
The collector output of 049 is passed through D95, VR11 and D93, and the
balance is broken by applying DC voltage to the balanced mixer to generate the
carrier. VR 11 determines the CW waveform of rise and fall by adjusting the carrier
level in R285 and C248.
At the same time Q48 is turned O N to turn OFF Q6 for keying isolation. C244
makes the OFF time of 0 6 longer not to influence the keying waveform.
The voltage is applied to IC17: B Pin5 in D95, and the output of Pin7 turns 046 ON
to set PTT line to LOW in D73, then the unit enters the transmitting mode. The
capacitor (C246, C247) is connected between Pin5 of IC17: B and the ground.
The holding time of transmitting is determined according to the discharge time
constant. BK1, BK2, and BK3 are the voltages tor the setting of 3*bit break-in time
constant. 8 stages voltage is obtained by the combination of the resistors R269,
R270 and R271.
In the Full Break-in mode, all of BK1, BK2 and BK3 are set to LOW, in the Semi
Break-in mode, one of BK1, BK2, or BK3 is applied the voltage.