CAPACITOR PROBLEM, PLEASE HELP

Discussion in 'General Electronics Chat' started by EDDY.B, Mar 29, 2009.

  1. EDDY.B

    Thread Starter New Member

    Mar 29, 2009
    2
    0
    Hi to all you knowledgeable techs out there,, My problem is that i need to replace a faulty potentiometer which is the "sender unit" to a digital numeric display.
    The faulty unit which is 1k ohm conductive plastic , has (or had) a 22-16 tantalum capacitor bridging two of the three terminals, and i am unsure which two !!!!!,, .Also, since i read that these caps are polarity sensitive, i would need to know which terminal to connect the pos side to.
    The input voltage to the display unit is 12 vdc, and the three output terminals (to the sender unit) have the following voltages present.
    (1) centre (wiper ?) to one side of resistance track = 2.1 vdc.
    (2) centre to other side of track = 0 volts.
    (3) across both ends of resistance track = 2.8 volts.
    Having spoken to a pal who is an electrician with limited electronic knowledge, he thinks the capacitor is purely a means of "smoothing" the signal, and possibly not essential, however i would prefer to have it in circuit if i can find the answer to this post, thankyou for your help.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Most likely between ground (0v) and the wiper.

    Resistors and pots are somewhat "noisy", akin to water squirting out of a hose through a nozzle. Sticking the nozzle in a bucket of water quiets the noise. Adding a bit of capacitance quiets down the electrical noise.
     
  3. EDDY.B

    Thread Starter New Member

    Mar 29, 2009
    2
    0
    Hi,Sgnt Wookie,,, thankyou very much for taking the time to help me with this problem,, Unfortunatly i am now rather confused having sent the same query to the tech support team of "Farnell" who suplied the replacement pot,, their answer was "connect cap across both ends of the track",, . I should also say that having paid for an "ask an expert" answer, the "expert" is of the same opinion as you with regard to the connection,, but in the light of no "definitive" answer my search continues,,, thanks once again,, Regards Ralph
     
  4. jjet

    New Member

    Apr 2, 2009
    3
    0
    The wiper is always noisy, especially old ones. The cap will help filter out the noise. Oxidation on the wiper is like opening and closing the circuit, noise. Even if you put the cap across the pot it wouldn't hurt anything, it just wouldn't do anything. If your worried, do both, it won't hurt. The cap should be marked for positive lead. If not, the short lead is negative. Good luck. JJM
     
  5. jjet

    New Member

    Apr 2, 2009
    3
    0
    Sitting in my chair, watching the History channel, I realized that I told you wrong about the polarity. Short is usually positive. It only takes one time working on a circuit someone told you was dead, after that you check it yourself. It's always best. Data sheet can be found anywhere. Sorry. JJM
     
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