Cpu And Peripheral Circuit - Alinco DR-135 Service Manual

3. Phase Comparator Circuit
4. PLL Loop Filter Circuit
5. VCO Circuit
7) CPU and Peripheral Circuits
1. LCD Display Circuit
2. Dimmer Circuit
3. Reset and Backup
4. S(Signal) Meter Circuit
The PLL (IC501) uses the reference frequency, 5 or 6.25 kHz. The phase
comparator in the IC501 compares the phase of the frequency from the VCO
with that of the comparison frequency, 5 or 6.25 kHz, which is obtained by the
internal divider in IC501.
If a phase difference is found in the phase comparison between the reference
frequency and the VCO output frequency, the charge pump output (pin 13) of
IC501 generates a pulse signal, which is converted DC voltage by the PLL
loop filter and input to the input to the variable capacitor of the VCO unit for
oscillation frequency control.
A Colpitts oscillation circuit driven by Q502 directly oscillates the desired
frequency. The frequency control voltage determine in the CPU (IC1) and PLL
circuit is input to the variable capacitor (D502 and D503). This change the
oscillation frequency, which is amplified by the VCO buffer (Q503, Q504) and
output from the VCO unit.
The CPU turns ON the LCD via segment and common terminals with 1/4 the
duty and 1/3 the bias, at the frame frequency is 64 Hz.
The dimmer circuit makes the output of pin 13 of CPU (IC1) into "H" level at
set mode, so that Q9 and Q3 will turn ON to make the lamp control resistor
R84 short and make its illumination bright. But on the other hand, if the dimmer
circuit makes pin 13 into "L" level, Q9 and Q3 will turn OFF, R84's illumination
will become dimmer as its hang on voltage falls down in the working LED
(D11, D2, D5, D3 and D6).
When the power from the DC cable increases from Circuits 0 V to 2.5 V or
more, "H" level reset signal is output from the reset IC (IC4) to pin 33 of the
CPU (IC1), causing the CPU to reset. The reset signal , however, waits at 100,
and dose not enter the CPU until the CPU clock (X1) has stabilized.
The DC potential of IF IC is input to pin 1 of the CPU (IC1), converted from an
analog to a digital signal, and displayed as the S-meter signal on the LCD.
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