Re: Apple II power supply capacitors

[et472@FreeNet.Carleton.CA (Michael Black)]

"Tom Zuchowski" (eamoncd@bellsouth.net) writes:
> "Michael J. Mahon" <mjmahon@aol.com> wrote in message
> 20040528205414.06123.00000076@mb-m13.aol.com">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! 

This is so true.  Back in 1974, I built a power supply a got a surplus
"computer grade" capacitor that's about the size of a Coke can.  A whopping
10,000, at about 18V.  It seemed like big stuff at the time.

IN more recent years, you can get the same capacity, with better voltage
rating, in a package about the size of a thumb.

In 1974, the big capacitor was impressive, not just in size but in
capacitance.  Now, it just seems bulky and obsolete.

  Michael