LA1235

No.873-7/12

Description of external parts

Part

No.

R201 Input resistance (Rg)

R202

R203

R204

R205

S meter adjust

Muting sensitivity adjust

Hysterisis adjunt

Large hysteresis.

Small hysteresis.

Current drain increases.

(Observe max. rating).

Muting sensitivity shifts to weak input

side.

R206

Muting drive circuit load Insufficient drive of detuning muting.

When driveing muting of LA3390

(MPX), make less than 200k

Ω to

prevent malfunction.

R207

Muting time constant

Abnormal detuning muting

attenuation waveform and abnormal

sound at the time of low frequency

modulation.

Muting response delay.

R208

IF-off voltage applying

resistnace

Large flow-in current at pin 5

(Observe max. rating).

IF-off does not occur.

(IF-off voltage

≥7.5V).

R209

R210

AFC, detuning muting

band width, tuning meter

deflection adjust

Large detuning muting bandwidth.

Small detuning muting bandwidth.

R211 Detection coil damping

Small detection output.

R212

S curve linearity

correction

Find such a value as to cause minimum distortion (THD).

C101

C102

C103

IF amplifier bypass

Unstable IF amplifier.

C104 S meter output bypass

IF system may be unstable.

C105

C106

Muting drive output

bypass

If low frequency AM compoent is

generated in IF signal, weak signal

muting flutters.

Muting response delay.

C107

C108

Muting drive output

smooth

Abnormal detuning muting

attenuation waveform and abnormal

sound at the time of low frequency

modulation.

Muting response delay.

C109

AF output LPF

Unstable IF system.

With MPX connected, separation

worsens.

C110

AFC output LPF

Muting attenuation worsens and

detuning muting bandwidth narrows.

Detunig muting response delay.

C111

C112

Constant voltage circuit

smooth

S/N, muting attenuation worsen.

C113 Power supply bypass

Unstable IF system.

L1

Power supply choke

Unstable IF system.

Large detection output.

S meter pointer is off zero point.

(In case of voltage drive type).

Function

Effect

If decreased

Causes matching wigh circuit of preceding stage.

If increased

Proper cares in using IC

• Connect the ground side of bypass capacitors of pins 2, 3 to an area close to pin 4.

• Connect the ground side of bypass capacitors of pins 6, 7, 10, 13, 16 to an area close to pin 14.

• Use the shortest possible wires for detection coil-to-pins 8, 9, 10 connection.

• Pin 13, being used for signal meter drive output, can be also used multipath detection because IF signal envelope

detected is output at this pin.