"Michael J. Mahon" <mjmahon@aol.com> wrote in message
news:20040528205414.06123.00000076@mb-m13.aol.com...
> John Van Winkle wrote:
>
> >I have read a few posts here about changing the power supply capacitors
> >in the Apple II power supplies.  I want to change mine before they have
> >problems so my Apple will stay working for a while.  Can anyone tell me
> >which ones should be replaced?
>
> Unless you have some earthshaking reason for doing this preventively,
> it is best to abide by the maxim:  "If it ain't broke, don't fix it."
>
> Getting into and working on the power supply is a lot more trouble than
> getting into and working on an Apple II.
>
> Further, no one can predict if and when a particular power supply is
> going to need work.  It depends on the precise manufacturing conditions
> of the capacitors in your supply, and on the complete history of that
> supply's operation and storage conditions.
>
> Trust me, it won't be any harder to do when you need to do it than
> it would be do do it now--and you might not need to for a long time.
>
> -michael
>
> Check out amazing quality sound for 8-bit Apples on my
> Home page:  http://members.aol.com/MJMahon/


I work for an electronics repair firm. My company's repair policy is to
replace the caps when they become 10 years old, and to always replace all
the caps in switching power supplies that are undergoing repair, regardless
of age.

But like Michael said, it is a real pain to get into the box!

To answer the question about which caps should be replaced, you need to
replace all of the electrolytics. The rest of this discussion will be about
cap replacement and may not necessarily apply specifically to the Apple II
power supply.

Electrolytics are generally can-shaped, and may have both leads on one end
and stand vertically, or may have a lead on each end and lie horizontally.
These caps will have polarity markings, one lead will be marked "+" or "-".
This polarity is very important, if you put one in backwards it will
probably explode. If the cap has no polarity markings, it may be
non-polarized and should be replaced with the same. Generally non-polarized
caps are physically large for their rating. Electrolytics have a crimp
around the positive end of the can, which helps distinguish them from
tantalums, which last much longer than electrolytics.

You will be amazed at how much physically smaller the replacement caps are.
Technology marches on! If you cannot find an exact replacement, higher
voltage ratings are just fine, and it is usually OK to vary
capacitance -20%/+50% from the original. You should use 105-degree caps in a
switching power supply. If all you can find are 85-degree, I would double or
triple the voltage rating, which should pose no problem since new caps are
so much smaller.

That's all I can think of at the moment. Hope it is helpful.

Tom Z