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    • #8250

        Hi all,

        All legacy blocks brushed and cleaned. Contacts are cleaned as well thanks to the great tutorial.

        Time now for doing some tests of the components.

        The meter is quickly tested with a resistor of 100K Ohm in series and connected to the battery.

        If the meter deflects to 9, which it should, then it’s time to move to the next step : a capacitor tester !

        In this test, we will check the leakage currents of capacitors.

        This is how it works :

        When a capacitor charges, the voltage across it’s terminals rises. The current flowing through this capacitor diminishes until zero when fully charged.

        Old or defective capacitors tend to leak current when fully charged. Our circuit is able to test these leak currents.

        This is the setup :

        Capacitor tester with legacy parts

        Operation is as follows :

        • For C1, you can use any capacitor of our Lectron legacy set (check the correct position for electrolytic capacitors !)
        • After connecting the battery, wait about 10 seconds.
        • Then keep pressing S1 whilst checking the meter.
        • You may see the meter deflect until it will reach zero. You might wait longer (1 minute or so) if the meter keeps deflecting.
        • Older and unused capacitors may need to be revitalized. This is a process whereby capacitors are charged during a certain amount of time and then decharged. by pressing S2.  This has to be repeated a couple of times. Always wait 10 seconds before pressing S1 !
        • If the meter keeps deflecting whilst pressing S1, the capacitor is probably defective.

        This is the working principle :

        When the battery is connected, current starts flowing through R1 and S1 (closed switch) and our discharged capacitor under test. This current slowly decrease as the capacitor charges.

        When we press S1 after 10 seconds, the capacitor should be charged almost completely (depending of the capacitor value). The meter shows currents up to 100µA.

        The current flowing now should be as close as zero (see graph below). After a certain amount of time the current flowing should be zero with a good capacitor.

        The Ge diode helps to protect the meter if a capacitor is defective and should leak current.

        Pressing S2 discharges the capacitor.

        Following graph shows the charging current versus voltage :

        Capacitor charging

        Many greetings

        • This topic was modified 4 years, 5 months ago by Michael. Reason: Changed font and size styling for easier reading
      • #8267

          Thanks very much Frank!  Not everyone has the benefit of Guenther’s magnificent testing devices so this is a great solution for our fellow Lectroneers 🙂 .

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