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Re: Magic smoke!

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D Finnigan <dog_cow@macgui.com> wrote:
> phigan wrote:
>> On 2024-08-26, D Finnigan <dog_cow@macgui.com> wrote:
>>> 
>>> if I have an extra capacitor. I think the last machine I had to replace
>>> was
>>> a Mac 512K. I may have ordered an extra then. 
>> 
>> Are there some known people or places that one can send Apple2 and
>> classic Macintosh units to for re-capping?
>> 
> 
> The Apple II isn't notorious for failing capacitors (except for this one in
> the power supply!), so I don't know of any services for this kind of work.
> I have heard of places for older Macintosh models, but I haven't used any of
> them. There were some people selling capacitor kits for Macs too, which
> could save some time as long as you did the work yourself.
> 

I agree that the capacitors used in Apple IIs are very reliable. In fact,
all the common capacitor issues are inside the power supply. 

There are two kinds of problems that are common:
electrolytic filter capacitors in the “line side” of the supply, and the X2
type polypropylene capacitor directly across the line input intended to
protect the supply from line spikes and reduce RF interference conducted
from the supply to the line. 

The second type (and the type reported by the original poster) is trivial
to dignose by the horrendous odor!  The X2 capacitor across the line has a
value in the 0.5-2.0uF range, and a 230vac rating. They are widely
available for under a dollar, and are made in a rectangular plastic
package.  The power supply will need several days of “airing out” before
it’s nice to be around. ;-)

The first (electrolytic) type of failure is rarely sudden (or odorous),
resulting from a long, gradual decline in filtering the raw 280vdc from the
bridge rectifier connected to the AC line.  If this happens, it decreases
the ability of the power supply to operate the computer.  There are usually
a couple of these, both the same rating:  about 100uF and 300vdc.  They are
also widely available, and it makes sense to replace them both. 

There is a more sudden failure mode of these electrolytics: shorting.  If
this happens, the fuse will blow, but often the bridge rectifier will also
be shorted, and it should be replaced before power is reapplied.

BTW, “re-capping” is an artifact of 1) old vacuum tube (hot, high voltage)
equipment, 2) old and not very reliable paper-insulated or wet electrolytic
capacitors, and 3) folks not very skilled in the repair of such equipment. 
The combination of these ingredients has led to an almost superstitious
tendency to “replace ‘em all”. This is almost never necessary, and often
results in needless damage.  

In the case of low-voltage, solid state electronic equipment, re-capping is
certainly unnecessary and potentially damaging.  (Note that power supplies
are NOT low-voltage.)

-- 
-michael - NadaNet 3.1 and AppleCrate II:  http://michaeljmahon.com

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Thread

Magic smoke! D Finnigan <dog_cow@macgui.com> - 2024-08-26 12:40 +0000
  Re: Magic smoke! phigan <phigan@bbs.penisys.online> - 2024-08-30 11:42 +0000
    Re: Magic smoke! D Finnigan <dog_cow@macgui.com> - 2024-08-30 21:15 +0000
      Re: Magic smoke! scott@alfter.diespammersdie.us (Scott Alfter) - 2024-09-03 20:12 +0000
        Re: Magic smoke! Andrew Roughan <no_email@invalid.invalid> - 2024-09-03 23:32 +0000
        Re: Magic smoke! Leon <nobody@nobody.com> - 2025-09-12 05:17 +0000
      Re: Magic smoke! Michael J. Mahon <mjmahon@aol.com> - 2024-09-04 23:18 +0000
        Re: Magic smoke! Andrew Roughan <no_email@invalid.invalid> - 2024-09-06 08:47 +0000
        Re: Magic smoke! phigan <wwiv@bbs.penisys.online> - 2025-02-24 00:18 +0000
          Re: Magic smoke! Andrew Roughan <no_email@invalid.invalid> - 2025-02-24 12:33 +0000

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