Question about MLCC

Discussion in 'Electronics Resources' started by Dukenukemx, Apr 6, 2012.

  1. Dukenukemx

    Thread Starter New Member

    Mar 18, 2012
    4
    0
    Trying to repair my car stereo and I'm testing some MLCC's. I'm testing them using a multi-meter set to beep when current passes. Two of which didn't show any conductivity. I painfully took two out of the circuit and tested them again, but nothing. Then I used my capacitor tester and got it to eventually read, but very low reading.

    Set to 200nF I saw .010 I believe. These capacitors are one of the first to get the antenna signal which leads to the IC tuner. That seems strangely low to me, and would maybe explain why the radio acts like it has absolutely no signal. Not even a hiss noise comes out of it, and can't seek a radio station.

    Can a mlcc really get that low in capacitance, and not even conduct a bit of power?
     
  2. panic mode

    Senior Member

    Oct 10, 2011
    1,320
    304
    impedance of capacitor is

    Xc=1/(j*2*pi*f*C)

    if you are just calculating magnitude, ignore j.

    i think 10pF should be about 160 Ohm at 100MHz. that is far from 'open circuit'.

    if capacitor is 0.010nF (10pF) that is quite ok for RF circuits. look at the FM transmitter circuits and you will see capacitors like 3, 5,10, 15pF...

    common way to test receivers is to work backwards. then each tested stage can become part of 'test lab'. for example check speakers (continuity is fine), if ok check audio amp (introduce some low amplitude signal or noise to it's input, you should hear it in speaker) etc.
     
  3. Dukenukemx

    Thread Starter New Member

    Mar 18, 2012
    4
    0
    Well, I had repaired the stereo by replacing the IC chip that sorta acts like a mosfet. So it produces sound through CD, SD card, and even plays DVD movie. I can manually change the radio station but I won't hear anything. It also won't find a radio station through seeking. So it sounds like a radio signal reception issue, or worse something wrong with the IC tuner chip. Though there's much more SMD components on this tuner. It's like a card that sticks out of the main circuit board that handles AM/FM.

    Then there's the crystal oscillator which I don't think I have the tool for testing that.
     
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