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Old 23rd Mar 2024, 12:30 pm   #21
John_BS
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

I think without specialist knowledge and test equipment you are sadly heading for a wrecked tuner.

John
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Old 23rd Mar 2024, 2:04 pm   #22
orbanp1
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Best to check the quadrature demodulator coil by checking its resonant frequency, not just the cap inside, it is tuned to 10.7MHz. It is easy to rig up a circuit with a signal generator and some detector (RF mV-meter, or scope) to check the resonant frequency.
Also, read up on how a quadrature detector works, there are a number of descriptions out there. In the descriptions they usually show in the phase shift network a capacitor, in your circuit it is an inductance, on the CA3089 datasheet it has a value of 22uH.
Best way to check the detector in your receiver by using a sweep generator and display/tune the S-curve, as suggested by John.
It is also more informative to measure the DC voltages on the IC pins as listed in the datasheet.
You also might want to try to change the LA1235 IC, it is available on eBay, and probably at other places.

Regards, Peter
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Old 23rd Mar 2024, 3:14 pm   #23
svetolik
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

I have swaped out Ic coil and capacitance of inside capacitor is 50pF, voltage on the pin 6 is now 3.5V instead of 1.8V, there is no more short between pins 8 and 9 and there is no output signal while signal meter shows full strength.
On the outside pins of IC coil I cannot find points where I can measure that 50 pF, so it is likely damaged and I will order another one. It is too sensitive and fragile to play with it.

Quote:
Originally Posted by John_BS View Post
I think without specialist knowledge and test equipment you are sadly heading for a wrecked tuner.

John
There where issues wit the mono too, fading out,crackling sounds on the switches, just good candidate for experimenting and for the wreck too.

Last edited by svetolik; 23rd Mar 2024 at 3:32 pm.
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Old 23rd Mar 2024, 7:17 pm   #24
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Quote:
Originally Posted by orbanp1 View Post
In the descriptions they usually show in the phase shift network a capacitor, in your circuit it is an inductance, on the CA3089 datasheet it has a value of 22uH.


Regards, Peter
Did you mean that capacitor from schematic inside IF coil is not there?
But how it is oscillating, electricity from cap goes into coil as magnetic energy and vice versa?
I have basic understanding of el. magnetic waves and FM modulation, but implementation in real integrated circuits without data is another pair of shoes.
One of the reason that I have posted it is to understand how this particular combo LA1235 and IF coil works because of its above decent performance, I can hear delicate details without distortion and it is not hard dry sounded as many quality quartz-synthesized tuners, sound is almost like a milk easy compared to them.
Also it will be interesting to understand how different circuits gives their modulation and impact on the output signal, beside measurements of distortion and noise.
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Old 24th Mar 2024, 1:12 pm   #25
orbanp1
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Here is a short description of the working of the quadrature FM-detector:
https://www.eetimes.com/a-quadrature...ator-tutorial/
In that explanation Cs, Cp, Rp, L forms a frequency sensitive phase shift network.
In your case, in your circuit, instead of the Cs capacitance a series inductance is used, that is the inductance of 22uH in the CA3089 application.
In your case that coil is part of that "T102" coil assembly.
In many cases, instead of a single Cp, Rp, L tuned circuit they use a double tuned circuit, like in your radio, it gives better demodulation linearity.

Regards, Peter
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Old 24th Mar 2024, 2:55 pm   #26
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Thank you for that I have remind my self on that phase shift detection-demodulation, having at the end changes in voltage swing according to changes in phase shift- frequency deviation compared to the carrier frequency.
But without capacity there is no oscillation, so no resonance with the carrier frequency, no detection of deviation and demodulation.
That added small coil is on the schematic, but explanation from the site is mix of theoretical citations, without clear connection to the example of implementation in the circuit.
Main question here is why infinity capacitance is measured across r120, assuming that is excesive, fault capacitance "Cp" from the model.
There is also possibility of damage to the coil and disconnetions od that thiny coils, "inductance of 22uH".
Maybe it is a small metalic part from the picture taken from the bottom of IF coil even I have measured 50pF across them on the second coil disconnected from the board?
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Last edited by svetolik; 24th Mar 2024 at 3:07 pm.
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Old 25th Mar 2024, 2:19 pm   #27
orbanp1
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

This is the redrawing of the detector principle circuit as it is in your radio.
Look at the block diagram on page 6 of the LA1235 datasheet and match the detector principle circuit to that.
There is no oscillator in the circuit, the signal comes from "Vin", the FM-IF signal in your radio, then there is the phase shift network, Ls, Cp, R120, and L (and the second set of L, C, R) and a mixer.
You are not able to measure the capacitance, unless you take the cap out of the coil assembly (not suggested, as you will probably destroy the coil assembly), you have a coil parallel with it!
The way to test the coil assembly is shown on the schematic, and the expected output.
The cap and inductance values might differ in your coil assembly, but the output should be similar.
You need a few extra components, a tunable signal generator around 10.7MHz, and a detector, like an RF mV-meter or scope.
Hope this helps.

Regards, Peter
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Old 25th Mar 2024, 7:54 pm   #28
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

I have measured capacity more like kind of primitive check.
When probes under voltage make contact with cap from IF coil- LC tank, charging of static electricity is started and than becomes discharging thru coil raising magnetic energy and vice versa. Accurate measuring capacity is no possible both with IF coil connected in circuit on the board or disconnected.
Voltage on pin 6 raised from dead stacked on to 1.8V to 3.5V only after pulling IF coil out.
Maybe this symptom is recognizable and fact that mono signal is demodulated.
I will check LA1235 data sheet for further explanation, meanwhile there is more on the horizon, pins from ordered IF coil do not match to the board.
I have also IF coil from old Dual tuner, it is for mentioned CA3089.
Does it possible to make Frankenstein Dunniko?
Connections of the IF coil are on the same pins 8,9,10.
On the picture is orderd IF coil taken from the bottom. Pins have different orientation.
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Old 27th Mar 2024, 3:09 pm   #29
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

I have put back IF coil back and get mono output only, while voltage on the pin 6 has stayed higher 3.6V compared to previous 1.8V.
Voltage on the TP2 is still dead on 5.6V
I have also changed main PS cap and few more, so in order to know what I am doing it is necessary to change them all.
There is a something like wax in the IF coil slug and on some places I can see tiny wire.
Is there proceed for safety turn it?
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Old 28th Mar 2024, 4:33 pm   #30
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

I am measuring 17.5kOhm R121 what could be explanation to have that 5.6V across, what is TP2 reference voltage.
In the service manual R121 is listed twice, with 6.8kOhm and 18kOhm.
I did not find any trace of earlier repairing attempt, so is that doubled values is for different IF coils?
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Old 28th Mar 2024, 11:20 pm   #31
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

W is for US, E is for Europe version.
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Old 29th Mar 2024, 9:34 am   #32
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

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.
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Old 29th Mar 2024, 1:06 pm   #33
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Your best course of action is to download the datasheet of the LA3401 stereo decoder and check out its operation based on that.
The datasheet describes in detail its use and application. That should help you find the fault.

Regards, Peter
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Old 30th Mar 2024, 6:11 pm   #34
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

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.
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Old 31st Mar 2024, 8:43 pm   #35
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

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.
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Old 2nd Apr 2024, 10:34 pm   #36
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

"When you tune slightly off center, the station is no longer in the center of the bandpass and the voltage will be a bit above or below zero."

Confirmed at 0.05V on to TP1 after adding more than 500pF across R120.
Also LA1235 is less hot, but sound is weak again followed with noise.
There is no difference in sound when switching muting off-on, no stereo but muting low signals is working.

Last edited by svetolik; 2nd Apr 2024 at 10:52 pm.
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Old 7th Apr 2024, 10:49 am   #37
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

No difference after replacing LA1235.
Voltages remains the same like old ones.
Only sensitivity has drooped.

I have added more than 500pF capacity across R120 in order to get 0V on to TP1, but output signal gets weaker already from -2V and what is interesting and maybe symptomatic is that adding only small capacity from start causes -6.5V on to TP1 and with adding capacity further rises to 0V.
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Old 13th Apr 2024, 10:50 am   #38
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Meanwhile, is there explanation for composite signal from LA1235 attenuation?

As I remember such feature exist since FM stereo is present, but not as mute function.

If it is possible to bypass it, maybe we figure out what is fault here.

I am wondering that the same behavior will occur with new IF coil connected.
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Old 23rd Apr 2024, 12:28 pm   #39
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

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.
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Old 23rd Apr 2024, 12:45 pm   #40
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Well done on your progress so far!
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