Icom IC-211 Instruction Manual page 43

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4. DIAL LOCK CIRCUIT
If the dial lock button is pushed, Pin 13 of IC8 goes LOW. Any switch chatter is
absorbed by R40 and C1. The output of ІС8 inverter is fed to Pin 11 (CK terminal) of
IC7. 1C7 works as a T type flip-flop and output levels are repeated every time the input
is applied. The O output from Pin 13 turns O4 ON, through R43, and shows that the
dial lock button has been pushed, by lighting the dial lock indicator LED, D7. Also
Pin 5 and Pin 9 of IC11, and Pin 13 of IC10 are connected to O4's collector and they go
LOW, so the clock pulses from Q8 and 09, the photo transistors, are not fed to the LSI
circuit, and the frequency is locked.
POWER SUPPLY UNIT
The power supply unit provides power for the set from an AC source. When using an AC
source, the AC voltage is reduced by transformer T1, and rectified by D4, a rectifier bridge,
and is supplied to the voltage regulator. The output of the bridge is filtered by C14, a 4700
microfarad capacitor. The regulator consists of D2, Q2, D3 and O1 on the side frame. The
regulated voltage then is fed to Pin 5 of SO1 and then goes to J10. The output voltage can
be adjusted by R13. When normal voltage is present, the emitter voltage of Q9 in the unit is
lower than the base voltage, thus it conducts and is bypassed, and the base voltage of Q1 and
Q2 remains low. When an overload or short occurs, the emitter voltage rises, cutting OFF
base voltage and thus it acts as a bypass for O2 and Q3. This circuit allows only low voltages
to be passed to Q2 and Q3. The action of the protection is instantaneous. When this occurs
even though the circuit is protected it is wise to turn OFF the power supply immediately
and trace down the trouble. The protection point can be changed by adjusting R5, a variable
resistor.
T2, D5 and C15 make up the AC memory power supply for the PLL LSI circuit.
When the memory switch on the rear panel is turned ON, AC voltage will be applied to T2
even if the power switch is turned OFF. Therefore rectified DC voltage is always applied to
the PLL LSI circuit and the LSI holds the previous operating frequency and the memorized
frequency.