LA1265

No.1820-4/15

3. Local OSC buffer output

• When local OSC buffer output wave form is saw-toothed at the SW mode, connect a resistance of 1.2k

Ω or

thereabouts across pin 22 and GND.

4. AM input pin

• It is desirable that the AM input pin (pin 19) be L-coupled to pin 18.

• Inputting to pin 19 can be done by DC-cutting with a capacitor. However, an unbalance in the RF amplifier

(differential amplifier) causes gain drop and whistle worsening.

5. Capacitance across pin 9 and GND.

A large capacitance across pin 9 and GND may cause a misstop

at an adjacent channel when the channel select speed is made

faster at the automatic channel select mode. In this case, decrease

the capacitance across pin 9 and GND. However, if too

decreased, the LED will flutter at low modulation frequencies at

the time of detuning. Therefore, it is recommended to fix the

capacitance across pin 9 and GND to be 3.3µF to 10µF. The

relation between modulation frequency and demodulation output

voltage on pin 9 with the capacitance across pin 9 and GND as a

parameter is shown right.

• LED lighting sensitivity setting for FM.

– For the LED lighting sensitivity setting for FM, the IC

input may be 45dBµ to 60dBµ. With the variations in the

front end considered, it is ideal that the IC input in a

standard receiving set be 51dBµ to 54dBµ. The lower

value of VR2 for the LED lighting sensitivity setting is as

illustrated right. Since the variations in the front end cause

the IC input setting sensitivity to vary, it is recommended

to use a value of VR2 at an input voltage lower than a

standard setting by 6dB or greater. For example, if IC

input 53dBµ is taken as a standard, use VR2

≤100kΩ at IC

input 47dBµ.

2. AM/FM changeover

• Two selections are available for changeover as shown below

: (A) pin 17-used method and (B) pin 18-used method.

range, distortion and selectivity will get worse.

• For (A), a resistance of 68k

Ω at the IFT cold terminal, which is used to prevent the changeover circuit from

malfunctioning, must be connected.

(A) pin 17-use method for AM/FM changeover

(B) Pin 18-used method for AM/FM changeover

IC input – dBµ

Semifixed Variable Resistor for FM

LED lighting sensitivity setting for FM

Ideal setting range

Modulation frequency – Hz

V9 – Modulation Frequency