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    quad capacitor?

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    JPW

    Posts : 6
    Join date : 2011-03-23

    quad capacitor?

    Post by JPW on Wed Mar 23, 2011 11:01 am

    Hello! I thought i had finished the re-buid of my Dyanaco Stereo 70, but on testing it, I read, from capacitor lug #2 to ground, (according to the instructions) only 100 Ohms, where as, the instrucions say the reading should be "in excess of one hundred thousand Ohms." Is the problem the quad capacitor, or might it be something else? All help would be appreciated! Thanks.

    GP49

    Posts : 718
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: quad capacitor?

    Post by GP49 on Wed Mar 23, 2011 11:24 am

    Desolder all the wires and remove them from that lug of the quad cap, then measure again.

    JPW

    Posts : 6
    Join date : 2011-03-23

    Re: quad capacitor?

    Post by JPW on Wed Mar 23, 2011 11:36 am

    thanks, GP49-I'll
    let you know!!

    JPW

    Posts : 6
    Join date : 2011-03-23

    Re: quad capacitor?

    Post by JPW on Wed Mar 23, 2011 1:41 pm

    The meter read open, without the wires attached...thanks again for the help.

    j beede

    Posts : 317
    Join date : 2011-02-07
    Location : California

    Re: quad capacitor?

    Post by j beede on Wed Mar 23, 2011 3:54 pm

    FYI: Harbor Freight sells a decent DVM for ~$40 that includes a capacitance function (up to 200µF). I have found it the capacitance function to be quite useful.



    Last edited by j beede on Wed Mar 23, 2011 9:39 pm; edited 1 time in total

    JPW

    Posts : 6
    Join date : 2011-03-23

    Re: quad capacitor?

    Post by JPW on Wed Mar 23, 2011 6:06 pm

    thanks, j beede...i've got a radio shack model digital multimeter.

    j beede

    Posts : 317
    Join date : 2011-02-07
    Location : California

    Re: quad capacitor?

    Post by j beede on Wed Mar 23, 2011 9:38 pm

    JPW wrote:thanks, j beede...i've got a radio shack model digital multimeter.

    Of course you have a DVM. The question is--does it measure capacitance? I have found that the "needle kick" or reistance measurement method can result in false negatives when testing (especially) electrolytic caps for failures.

    JPW

    Posts : 6
    Join date : 2011-03-23

    Re: quad capacitor?

    Post by JPW on Thu Mar 24, 2011 9:10 am

    J beede: I got a radio shack multimeter with capacitance reader on it- I should have been more clear! -the capacitance reads good from the capacitor lug #2 to ground; around 30microF's, and so do the rest of the lugs-25 to 35 microF's. I suppose this means the capacitor is good? any ideas what could be wrong in regards to the resistance? thanks.

    GP49

    Posts : 718
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: quad capacitor?

    Post by GP49 on Thu Mar 24, 2011 10:53 am

    Since you reported 100Ω with the wires connected, and normal capacitance on the quad capacitor with them disconnected, that 100Ω had to be on one of those wires. Your next step should be to find which of those wires now has the 100Ω resistance measurement to ground and trace that circuit until you find the fault.

    JPW

    Posts : 6
    Join date : 2011-03-23

    Re: quad capacitor?

    Post by JPW on Thu Mar 24, 2011 1:26 pm

    thanks, you guys! I traced back from the capacitor to the PCB, and that is where I found the error: a capacitor was miss-placed on the board. I re-soldered it and everything checks out. thanks again.

    j beede

    Posts : 317
    Join date : 2011-02-07
    Location : California

    Re: quad capacitor?

    Post by j beede on Thu Mar 24, 2011 9:42 pm

    JPW wrote:J beede: I got a radio shack multimeter with capacitance reader on it- I should have been more clear! -the capacitance reads good from the capacitor lug #2 to ground; around 30microF's, and so do the rest of the lugs-25 to 35 microF's. I suppose this means the capacitor is good? any ideas what could be wrong in regards to the resistance? thanks.

    Kudos to Radio Shack for offering a DVM with a capacitance function. One thing to remember... measuring capacitance at low voltage (like our DVMs do) may be be a whole different kettle of coulombs than measuring capacitance at the high voltage that the quad cap actually runs at. In any case I have made good use of the capacitance function.
    ...j

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: quad capacitor?

    Post by tubes4hifi on Fri Mar 25, 2011 11:44 pm

    very true - a high voltage cap might test fine with a multimeter that is using a 9v battery, but it may not work well with 400+ volts on it !!
    an easy sign of a cap that is failing is that it is warm, not from the tubes near it, but from internal resistance and leakage

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