Marantz service manual - tuner section enhancement

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tranguru

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Hi team

I am in the process of enhancing some service manuals. I have converted the one for the 4400 and 2230 to MS word.
Note that MS-Word documents cannot be saved on this site.
PDF is not an option as the document should remain editable

I have added some comments to the FM tuner circuit description - I am doing to educate myself on how these things work and to record some extra repair information. sharing with others would be great too of course
I am sure I did not it all right and many parts could be much better.
it is quite long: I took the SM text and added information. my dream is to be able to explain each component in the tuner section.
thanks for anyones feedback
Here it is :
1 FM TUNER
1.1 RF and IF Circuit

The FM Tuner section of Model 2230 is divided into five functional blocks:

1. FM Front End

2. IF Amplifier

3. Detector

4. Muting Control

5. MPX Stereo Decording Circuit.

1.1.1 FM front end
FM signals induced by a FM antenna are led to FM antenna coil L101 through an attenuator switch and a Balun coil – L001.

A Balun coil converts between a balanced signal (two signals working against each other where ground is irrelevant) and an unbalanced signal (a single signal working against ground or pseudo-ground) and connects lines of different impedances.


These signals are then applied to the FET RF H101 amplifier which in turn applies its output to the next FET Mixer H102 through the double tuned high selective circuits.

The mixer is used to convert the FM input frequency (ranging from 88 MHz to 108 MHz) to the intermediate frequency of 10.7 MHz.

The mixer combines 2 signals:

· Input frequency F1 from the antenna – after tuning and amplification by FET RF H101 amplifier

· Local frequency F2 generated by local oscillator build around H103

The mixer generates a set of combined frequencies (nF1± mF2, where n and m are integers)):

· F1+F2, F1-F2 which are the main frequencies which have the most energy or output level

· a set of harmonics, 2F1+F2, …. Which are weaker than the 2 main ones

For the FM tuner, we are only interested in F1-F2. F2 is such that F1-F2 = 10.7MHz.

Why not F1+F2? because it is easier (cheaper) to work with lower frequencies if the filters that follow.

A set of filters will eliminate F1+F2 and the harmonics in the next stage: the IF amplifier

The FET Mixer convert its input signal into 10.7 MHz intermediate frequency and amplifies it at the same time.

The H103 is a local oscillator and its output is injected into the source of the FET Mixer, the injection voltage is about 700 mV.

The 10.7 MHz front end output is fed to the next IF amplifier unit through a coaxial cable.

More info: http://www.interfacebus.com/dictionary-of-terms-mixer-circuit-description.html

1.1.2 IF amplifier
The IF amplifier unit consists of seven IF amplifier stages and one AGC amplifier stage. Eight ceramic filters are also used to obtain high selectivity- and four symmetrical diode limiter stages are employed for the best limiting characteristics, improved capture ratio and good AM suppression.

AGC stands for Automatic Gain Control. The AGC is used to ensure the IF stage signal input level does not vary (too much) è even if the different the channels have different strength levels, you don’t hear is too much the variations in the audio.

A part of FM Front End output is applied to the AGC amplifier H209 and its rectified output is fed back to the gate of FET RF amplifier to decrease the gain with increased signal strength.

The eight ceramic filters are F201 – F208. They are SFA 10.7 MC in the parts list. The perfect filter lets only one frequency plus a channel spacing pass thru it: 10.7 MHz.

As they are not perfect eight are needed.

Note that these channel spacing allow the actual audio signal, typically ± 100 KHz around the 10.7MHz.

Those 200 Khz contain:

· the FM mono signal : 30Hz – 15Khz

· the stereo polite signal (turns stereo decoding on and off) at 19KHz

· Stereo audio in the form of Left minus Right channel

· Some other info such as RDS – not used in the 4400.

See typical filter and FM spectrum specifications: http://www.axinotech.co.nz/documents/Bandwidth needed for FM broadcasts.html

· The composite baseband signal section

· Receiver filter section figures: 4 and 5.

upload_2017-5-3_15-40-31.png

Reference: http://www.maxlink-cn.com/top/about4.asp?id=100&class=2&name=Crystal Filters

The signals required for multipath indication are obtained from the five stages of IF amplifiers through coupling capacitors C252, C211, C214, C223 and C228 respectively and rectified by five pair of full wave diode circuits. Thusly obtained AM components from the FM signal are appropriately mixed and applied to the vertical amplifier for multipath display.

1.1.3 FM detector
The detector converts the modulated signal to a signal the FM demodulator can use to make mono, and stereo signals.

It detects the frequency variations from the FM signal. The frequency accelerates (expands) and decelerates (compressed) based on the input (audio) signal.

upload_2017-5-3_15-40-46.png

The bottom is the incoming signal

The detector has “S” curve function to demodulate:

upload_2017-5-3_15-41-2.png
Source:

http://www.radio-electronics.com/in...eption/fm-demodulation-detection-overview.php

The IF signal sufficiently amplified through each stage of IF amplifier is finally applied to the Detector Amplifier H208.

The detected audio output is fed to the buffer amplifier H210 and its buffered output is fed to:

A. noise amplifier H310 through resistor R378 and capacitor C333,

B. QUADRADIAL OUTPUT Jack on the rear panel through resistor R379,

C. MPX stereo decoding IC (H321) through R301 and H301.

Buffer amplifier is used because the H208 does not have enough power to drive the 3 components above è output of detector (thru H208) is current (not voltage) amplified.

1.2 Audio Muting and Stereo Mode Auto-Selecting Circuit
The muting circuit consisting of all solid-state electrical switching has been incorporated in the Model 4400. Three inputs control the muting function:

· The first is related to signal strength,

· the second to the noise condition at the detector

· The third is derived from the DC component of the detector output. This the “S” curve detection

These inputs are properly matrixed and gated to provide muting free from noise and transients.

1.2.1 Signal strength input
The first input of DC voltage obtained by rectifying a part of IF output signal from the H205 and H206 is applied to the base of H308 and turns it on, if the IF output is greater than pre determined level (muting threshold level). When the H308 is turned on the H309 is turned off, allowing the emitter-collector resistance increasing and the collector voltage rises about 9V. The increased collector voltage increases the gate bias voltage and turns on the switching FET H301, decreasing the source-drain resistance to near zero ohm and allowing the audio signal applied to the source to flow to the pin (2) of decoding IC through the source-drain path.

When the input signal is lower than predetermined level, the DC output obtained is small and can not turn on the H308, thus the H308 keeps its turn-off stage and this makes H309 turn on, decreasing the collector voltage and turning off H301. Thus no audio signals can pass through the FET. This is the fundamental principle of the muting operation but for more elaborate muting operation the second and the third inputs are necessary.

1.2.2 Noise level at detector
The second input is used to protect the muting operation and MPX stereo beacon lamps from misoperation due to undesirable noises. The high frequency noises included in the detected audio signals are separated by a small capacitor C333 and amplified by the noise amplifier transistor H310 and its output is rectified by the two diodes. The rectified DC output is proportional to the noise components in the audio signals.

When there are excessive noises in the audio signals such as obtained with a station incorrectly tuned in, the rectified DC output turns on the transistor H311, decreasing the emitter-collector resistance to zero. This means the collector of H309 is short-circuited to the ground, therefore the H301 is turned off and any audio signals having excessive high frequency noises cannot go through the FET's source-drain path.

The transistor H317, also, turns off when transistor H309 or H311 turns on, and turns on the transistor H303 connected to pin (8) on the MPX decoding IC. Pin (8) is therefore grounded equivalently to set the IC in the monaural mode of operation. This prevent misoperation due to undesirable noises when the FM tuner is out of tuning.

1.2.3 “S” curve discriminator
The third input is obtained from the FM discriminator circuit. The DC output so called "S" curve is applied to the gate of H312 through a resistor R281 and dividing network (R361 & R362). The DC output is zero with a station correctly tuned in, but will vary from negative to positive values or vice versa when the tuning point is deviated toward either plus or minus frequency from the correct tuning frequency.

When the DC output is increased to a greater level than that of predetermined one, the increased source potential of H312 makes the transistor H315 turn on (this means the collector of H309 is short-circuited to the ground), ... H301 turn off, ... H317 turn off, ... H303 turn on. This grounds pin (8) of the MPX stereo decoding IC, therefore the decoder is set in the monaural mode of operation and the stereo indicator lamp turns off. When the DC output is increased to the negative predetermined level, the decreased source potential turns off the H313 which in turn makes the H314 turn on (This means the collector of H309 is short-circuited to the ground).

The subsequently changes are exactly the same as that just described above.

Thus when the tuning is shifted or deviated to the certain frequencies in which undesirable noisy side-audio signals are produced, both muting and monaural/stereo Switching Transistor H303 are operated automatically and open the circuits.

With the station correctly tuned in, the bias current of the FET H312 is adjusted so that both transistor H314 and H315 are not turned on, giving no effect on the transistor H309.

Extra notes (source: Tom on Audiokarma):

Intermediate Frequency (IF) signal strength is monitored by H308. If signal strength is above muting level, H308 is ON, H309 is OFF.
If there is excessive noise, then H311 is ON which is wire-anded to H309 keeping H301 (FET) OFF.
If the discriminator is outputting DC due to the tuning being off station, either H314 or H315 is ON which are wire-anded to H309 as well. This also turns H303 ON grounding Pin 8 of the decoder forcing MONO operation.
If the station is properly tuned, not noisy and the signal strength is high enough,
H308 is ON, signal strength OK
H309 is OFF, signal strength OK
H311 is OFF, Noise is OK
H314 is OFF Tuning centered
H315 is OFF Tuning centered
H317 is OFF, signal strength , Noise and center tuning OK then:
H301 is ON allowing audio and MPX signal to pass into the decoder.
H303 is OFF If signal strength sufficient for Stereo operation and MONO button is not pressed
H302 is OFF VCO runs (AM not selected)
 

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Outstanding! I have obtained a recommended book about AM-FM-FM Stereo theory, diagnosis and repair and have been plowing into it lately. (Can't remember the name, it's at home. But it was recommended on this site.) Anyway, your expanded information just reinforces what I have been reading. Seeing it in the context of the service manual info is very enlightening. Thanks!
Steve
 
This is great ! Explaining the tuning section on an actual Marantz really helps me understand the vague (to me) alignment section of most Marantz service manuals . Steve the book you were referring to might be "Trouble Shooting, Servicing, And Theory Of AM,FM,& FM Stereo Receivers" . No wonder you couldn't remember the name.
 
I can send the full word document to those who want. all I need is an email because it cannot be uploaded here.
formatting is much cleaner than what I copy pasted here.

Note that I also want to enhance the amp and pre amp sections

luck
Robin
 
This is great ! Explaining the tuning section on an actual Marantz really helps me understand the vague (to me) alignment section of most Marantz service manuals . Steve the book you were referring to might be "Trouble Shooting, Servicing, And Theory Of AM,FM,& FM Stereo Receivers" . No wonder you couldn't remember the name.
Yep. That's it. I was lucky to find a copy out of Canada that was in nearly mint condition for $9. It sometimes sells for $200. Very well written and understandable by a non-engineer.
 
Count me in as interested, too. I really want to learn more about these tuners and your efforts are greatly appreciated.
 
Thanks all

I can send what I already have.
I have add some more info. focusing on the 4400 for the moment.
the 2230 is pretty much the same, except for the MPX decoder - IC H1156 in 4400, full discrete in the 2230 (and the 18, 20, 19,..) ==> next level for me...

Note that the more I dig the more questions I have.
I posted a question to the tuner experts on AK - lets see what comes out.

br
Robin
 
Fantastic post!

I also have the book listed above, very informative.

Another great source is the manuals that come with the Sencore alignment generators.
 
Another great source is the manuals that come with the Sencore alignment generators.
Yes, I've been studying that also. Very informative. Of course, it's all academic for me since I haven't actually done any of it. All of my stuff is in storage right now as I'm in the process of moving. Can't wait to get set up again and do some hands on with this alignment information I have picked up.
 
I check the manual of the SG165 - great indeed.
at some point I will try to take pictures of the waveforms thru the different tuner stages.
I noticed my TEK TDS 430A has an FFT function.... so I have a kind of spectrum analyzer :banana: so I will add that part too.
not on the 4400 though, the IF amp is under the amp and MPX is under the AM board...

Robin
 
Hi all,

I will add some info to the current version and make it available.
  • in PDF: I will upload it to AK
  • you want the MS word version:just send me your email adrs as I MS word documents cannot be uploaded to the site.

Robin
 
You should distribute your notes as a companion to the service manual rather than as a revision of the manual. Include a link (only) to download the manual from your original source.
 
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