Alinco DX-SR9 E, Service Manual

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The signal input is amplified by the Q803 to about 100mW. By having the idling
current of about 100mA the amplification is A-class. With the feedback the
frequency response is compensated, and with a capacitor parallel to the
emitter resistor the frequency is compensated totally. Then the signal is
amplified to about 5 watt with the Q801 and Q805 (RD16HHF1) where the
idling current is 800mA (adjusted with the VR804) in push-pull configuration.
The D804 and D805 is thermally contacting the Q801 and Q805 to compensate
idling temperature.
There is about 1.6A of idling current in the final amp circuit consisting of the
Q802 and Q804 (RD100HHF1). The D801 and D802 are thermally conducting
with the Q802 and Q804 for temperature compensation. Feedbacks exist thru
the R804 and R822 from collector side averaging the gain in a wide range. The
output of 100W goes to the filter circuit. The collector current of the Q802/Q804
is detected due to the voltage drop caused by resistance of the FB803 and
L801, and is output to the main unit.
The fan is controlled under the temperature of the Q802 and Q804 which is
sensed by a thermistor (TH801). While transmitting, due to temperature rise,
the resistance of the TH801 goes down and voltage of inverted input for the Pin
No.1 of IC101 (MAIN UNIT) goes down. The IC101 (Pin No.1) input is applied
a voltage corresponding to its voltage thus is compared. When the temperature
is over 50 degrees Celsius approximately, the inverted-input voltage would go
down with comparative voltage, and by the comparator output voltage of the
Pin No.74 of IC101, the Q183 is turned ON and the fan starts running.
As a protection for the final power amp, power down circuits detecting SWR
excessive current, and temperature rise have been installed.
2. PA Unit
a. Power Amp
b. Final Power Amp
c. Cooling Fan Control
d. Protection Circuit
The D179 and R457 help to follow speeding up the keying, while the D176 and
R458 determine the discharging time constant in transmission and elongate
the time constant in reception so that it compensates the time constant
recovery during the reception. By doing this, the circuit can follow the keying
speed; transmission can continue between letters; and reception can take
place between words. The circuit is good typically between 30 characters per
minute to 200 characters per minute.
The forward voltage obtained in the PA unit correspondent with transmit power
is input to the IC118:A for invert amplification. At the non-inverting input there
is a voltage, and the output voltage is shifted by the non-inverted input voltage.
There is already about 4.0V on the ALC line which is applied to the second gate
of amplification stage that is under ALC control. When a forward voltage is
applied, the output voltage of the IC118:A goes down, and when becomes
lower than about 3V, the D160 lowers the voltage of the ALC line. The VR112
is for adjusting the Tx output to 100W (High power). The VR119 is for adjusting
the Tx output to 10W (Low power). The VR120 is for adjusting the Tx output to
1W (super Low power). By I is soldering, Q166 turns ON and by having the
VR114 in parallel the voltage is brought down to result in 50W. When in AM,
the R448 comes in parallel to lower the output to 40W. When in Low power, the
LOW line brings the R528 and VR119 in parallel to lower the voltage. When in
super Low power, the slow line brings the R529 and VR120 in parallel to lower
the voltage. The Q158 and VR113 are for making the (antenna matcher) TUNE
output to 10W output. Necessary output, however, may be different depending
on the automatic tuner. When the SWR is high, reflected voltage turns on the
Q158 lowering the power. The Q158 is activated from SWR 3 approximately.
The voltage difference detected in the PA unit by the final collector current us
differentially amplified by the IC118:B. The output voltage lowers as current
increases and at some point the ALC line is pulled down thru the D160 lowering
the output power. The operating point is determined by the VR110.
The forward voltage is amplified by the IC118:D for driving the meter. The
D164, R433 and C419 are for instant peak-holding to show the meter more
visible. The D163 and D136 switch to S-meter. The ALC voltage is invert
amplified by the IC118:C. The output voltage is divided from 8V thereby
lowering the feedback resistance so that tolerance caused by bias-leakage is
minimized; further this feedback resistor lets some current to the R423 to
obtain 4.0V to the ALC line. The output is fed to the base of the Q150, leading
to the front unit tell the CPU to switch Tx and Rx besides illuminating the Tx
LED.
h. Power Control/ALC Circuit
i. Overcurrent Protection
j. RF meter circuit, ALC indication