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12219Capacitor testing

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  • Mike Loewen
    Apr 6, 2009
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      I tore apart my IMSAI in order to remove the four large electrolytic
      capacitors for testing/reforming. There are two 9500uf-30VDC caps and two
      95000uf-15VDC caps. Here's the rig I put together for bringing them back
      to life:

      http://sturgeon.css.psu.edu/~mloewen/Oldtech/IMSAI/Reforming-L.jpg

      I put this together after reading many documents about testing old
      capacitors. Hidden behind the cap is an 8K power resistor in series with
      the cap. The small meter is measuring the voltage output from the the
      power supply (a HP 6443B 0-120VDC/2.5A unit), in this case 25.0 volts.
      The large meter is measuring the current flowing through the cap, 0.11ma.
      The voltage across the cap is 24.7V at this point.

      I started out by raising the voltage by steps, from 3-6-9-12-15-20-25,
      watching the current and making sure it went no higher than 0.5ma. At
      each step, I'd let the cap charge up until the current was down to about
      .05ma then increase the voltage. Once I got to 25.0 volts, I let it sit
      for a while until the current was down to .03ma.

      So far I've done one of the 9500uf caps. I'm hoping this procedure is
      effective. How about it, Dan and the rest of the electronics gurus?


      Mike Loewen mloewen@...
      Old Technology http://sturgeon.css.psu.edu/~mloewen/Oldtech/
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