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 200kΩto
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.