Nikko NT 950 Tuner, no stereo, low level mono output signal

[Svetoklik]

Now listening audio signal directly from pin 6, LA1235.
There is no signal when muting is switched off, so it will be good to know how switching works in order to find out where is the fault.
So the signal is coming to the stereo decoder LA3401, but there is no decoding

 

[Svetoklik]

Measuring 8V on to pin 5 (signal from LA1235) instead of 3.2V according to data sheet for LA3401.
I will test triggering stereo and performance with different values of components from data sheet.

 

[Svetoklik]

I have changed el cap C121 on the pin 9 and finally get 0V on the TP2 with paralleling caps to IF coil, across R120.
Muting is working now, but there is no signal for stereo even when muting is on and I can hear output signal when strong signal is present, opposite to weak or no signal case, when muting is activated and there is no signal on the output.
Automatic scanning working too now, what means that detection is activated, but I am not sure does it stop when stereo signal is detected only.

 

[Svetoklik]

I have swap CA3089 with LA1235 in old Dual tuner CT1640, only pin 16 has to be grounded in parallel with RC values from data sheet and viola, got dead quiet background with more sensitivity.
That Schimit circuit of LA1235 works tightly and more interesting there is no more occasionally nasty highs despite that decoder from dual has THD over 10kHz like vertical line exposed.
So IF coil for CA3089 is compatible with LA1235, got stereo and detailed sound without distortion having impression that I am in broadcast studio.
But bass is lacking compared to CA3089 and I will go for that Dunikko Frankenstein tuner in order to get better decoder.
Is someone familiar with FM distortions?
Very interesting area.

 

[Svetoklik]

Here is a schematic of Dual CT1640.
I would like to hear more about its front end.
It looks like 7 LC resonance circuits without amplification between what I consider as better from my basic knowledge and intuition.

 

[Svetoklik]

Finally got that Dunikko stereo signal, now playing from LA1235 implemented in Dual tuner and connected to the LA3401 PLL decoder on to Nikko tuner.
The quality of sound is with more details and more mid bass energy, but I cant measure it. and confirm anything precise.
There is indication for stereo signal on the Nikko without any signal strength indication