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No idea about this tuning capacitor

Discussion in 'Datasheets, Manuals and Component Identification' started by Number, Jun 9, 2013.

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  1. Number

    Number

    65
    0
    Jun 9, 2013
    Hello all! I am having one heck of a time trying to figure out how I should/need to wire this component to get use from it. Google has yielded some help but nothing that definitely answers my question: How do I connect this component? :confused:

    The first thing I did was Google variable capacitors, which got me off in the right direction, but after finding out it's typically called a tuning capacitor, it eventually led me here. :cool:The part maker is Mitsumi and the model listed on the product itself PVC-2LXT-L. I did locate one data-sheet however it did not specify how to connect the pins to one another. I would relate it to having a 555 timer for example and knowing what all the pins do, but not actually knowing the pin numbers. That makes it useless if you do not know that information.

    My oscilloscope was the first thing I turned to, which mind you I have only owned for one week, and I was going to connect the capacitor up how I felt it would naturally be, which is that the pins, 3 on each side, the middle was ground & the other two were your anode and cathode respectively. I suspected that when the capacitor was going up or down in capacitance that this would somehow alter the amplitude of a wave or the frequency, neither of which I observed (for what it's worth).

    My next stop was Instructables, but that site has been buggy for me as of late, so here I am bringing this issue to you all. And rest assured, the answer to this thread I will be making a tutorial/how to video of this component so someone else done the road can hopefully find an answer. :)

    This information may or may not be relevant, but I did salvage this unit and about 4 others from older (80's/90's) AM/FM radios/stereos/boomboxes. So their purpose is clearly for tuning and manipulating frequency/amplitude of waves, I just can't get it to do so.
     
  2. poor mystic

    poor mystic

    1,071
    33
    Apr 8, 2011
    Hiya there Mr Number :)
    You need to study up about LC tanks, which are used for their tunable resonance. Tuning is achieved by changing the capacitance - the "C" in the LC. The "L" is an inductor - often a great length of very fine wire wrapped around a ferrite rod.

    With your oscilloscope, you could possibly (depends on both the 'scope and the circuit in which the cap is used) see a change in the frequency of a signal on one of the pins of a tuning capacitor in a radio that works. Whether or not your 'scope will help you with this, you could watch the way a tuning cap's geometry changes as you move the tuning knob of the radio. This would help you see how a varying capacitance is used.

    Until the capacitor is wired into a powered resonant circuit you will find it difficult to see how it is used. You need background information.

    I'm sorry I haven't directly answered your question. I'm in the middle of technical writing about electricity right now as my main effort, and to properly explain what you need to know would take a lot, I mean a lot! of work. But face-to-face, with circuits to hand, I could show you in 5 minutes.

    You could always post a good photograph and I or some other will soon point out the terminals, for what good it'll do you.

    I recommend that you join a radio club such as the ARRL (if you are in America) or the equivalent club in your country. That'll help heaps!

    Mark
     
    Last edited: Jun 9, 2013
  3. Number

    Number

    65
    0
    Jun 9, 2013
    I've used Tank Circuits before and I know their purpose/function, but I definitely could learn more about them, that's for sure! I'll post a picture or a video to describe what it is that I've having trouble with and I'll also link the datasheet I found. Thank you for the reply as well. :)
     
  4. Number

    Number

    65
    0
    Jun 9, 2013


    This is a video I made to try & describe the tuning capacitor. It should help. :cool:
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    your 4 red wires are connected to the bolts which hold the device together. They are probably not used for electrical connections.

    The solder tags are almost certainly what are used for the connections.

    As per the datasheet, the device has 2 variable capacitors, one for AM and the other for FM.

    This application note shows you how it is used.

    A careful inspection should reveal which of the solder tags are connected to what.

    Alternatively a capacitance meter can be used. When connected up correctly you will see the capacitance change as you rotate the shaft.
     
  6. Number

    Number

    65
    0
    Jun 9, 2013
    So a lot of strange things happened when I connected it up differently. I now know one of two things: (a) My multimeter is crap or dead, or (b) My variable capacitors are crap or dead. One of them is for certain.

    While I wired up the VC to the middle pin on the top & bottom, my capacitance was all over the place! I got ranges from 0.2nF to 218+uF. And while the multimeter was connected to nothing I got higher readings from air than in the VC. That boggled my mind just a bit.

    I connected my oscilloscope to it and gave it some juice from my 9V AC power supply. The thought was that I could see something change. Surely a change in capacitance would affect the waveform of the AC Sine Wave @ 60Hz. However, All I got when I tried to turn the shaft was a massive spike in the graph, note that it just blew up, it did not actually change amplitude or frequency; it was essentially just zoomed in.

    So here I am at a crossroads. If the variable capacitor works, it means a lot of new & fun projects, if it doesn't I'll probably just term them open and see how it works, then donate to my local electronics warehouse.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    1) Check your meter against fixed capacitors in the range of expected capacitances of the variable capacitor.

    2) try various combinations of connections until you find those which read sensible values
    9V AC (60Hz?) has a frequency far too low for this capacitor to do anything to (it will essentially appear to be an open circuit).
     
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