Apple III main capacitor replacement question...

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Joined: Aug 8 2014
Posts: 42

Hello,

So I got this beautiful Apple iii in from 1978appleii.

Whelp the mains blew on it right before she shipped it out to me. It sticks horribly. I'm going to replace the cap but I can't seem to find the voltage for it. I know it's a 22uf but does anyone else have the specifics so I can order it.

Also it looks at though the board has been recapped. Anyone else see these caps before?

Thanks
Samm

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Offline
Joined: Apr 11 2006
Posts: 1013
Re: Apple III main capacitor replacement question...

Those caps look pretty typical. And the filter cap blowing is very, very typical. The replacement filter caps I use are 275v.

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Joined: May 27 2013
Posts: 794
Re: Apple III main capacitor replacement question...

If by any chance you cannot find a cap with the voltage rating that you need, then there are several general guidelines to follow. I am assuming the information I am about to give will be of use to you since you have run into a problem which is easy to resolve.

1). The caps from the time these computers were made were larger than the ones used today. This means that using a replacement cap from today with the same physical size of the original will in general have a larger voltage rating.

2). The voltage rating is an indication of the voltage the cap can withstand without blowing itself out or leaking. In most cases you may replace the original cap with one of a higher voltage rating but don't go too high.

3). Never select a cap with a lower temperature rating than the one that you are replacing unless you are sure that the cap will never be exposed to such temperatures.

4). If you go to Digikey, you will find other characteristics for caps that you may select. For example, lead spacing, ESR, physical size, radial or axial, etc,.

5). If you are replacing a polarized cap then replace it with another polarized cap.

6). Never buy a cap that is known to have been manufactured with the stolen formula.

Read this website for details:

http://www.badcaps.net/index.php?s=62bb87cb71136174a33c0e09e9cbec50&pageid=causes

Offline
Joined: Aug 8 2014
Posts: 42
Re: Apple III main capacitor replacement question...

david__schmidt wrote:

Those caps look pretty typical. And the filter cap blowing is very, very typical. The replacement filter caps I use are 275v.

Thanks bud, that's what I was looking for!

Samm

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Joined: May 27 2013
Posts: 794
Re: Apple III main capacitor replacement question...

In the future, when you grow on to work on more complicated circuits, you will then have to take into consideration things like ESR. Each circuit when designed properly must take into account it's purpose, function and tolerances.

Now that you have started out, do some research on ESR. This will help you familiarize yourself with the wonderful world of electronics.

Read these articles:

https://en.wikipedia.org/wiki/Equivalent_series_resistance

http://forum.allaboutcircuits.com/threads/understanding-capacitor-esr-ratings.28175/

When starting off, you may want to avoid those articles which use too many scientific explanations. They typically explain how everything works, but don't do much in terms of cap replacement. When you move onto that level you will need that info for designing circuits.

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Joined: Aug 24 2013
Posts: 46
Re: Apple III main capacitor replacement question...

Samm328 wrote:

I know it's a 22uf but does anyone else have the specifics so I can order it.

Samm,

I had one of these let go this past weekend on a IIgs. Note that it is 0.22uF, and not 22uF.

For reference, mine is marked PME 271 M, with a 20.3mm lead spacing, although a hole exists for a 22.5mm spacing as well.

These are "safety rated" and should be replaced with an X class capacitor.

Some alcohol cleaned up the residue from the smoke and greatly reduced the smell.

Mine didn't blow the fuse, and I removed it while I wait for a replacement. In my IIgs power supply, there are two of these, and a pair of smaller 4700pf Y class capacitors as well.

In your image, I also see an X-class 0.1uF capacitor.

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Joined: May 27 2013
Posts: 794
Re: Apple III main capacitor replacement question...

My God... ChristopherB, you are RIGHT! These are safety caps all right.

Samm, read this thread to get familiar with them:

http://www.applefritter.com/content/apple-iigs-power-supply-question-3

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Joined: Aug 8 2014
Posts: 42
Re: Apple III main capacitor replacement question...

Just so everyone knows I was simply asking for the specs. I actually know computers quite well. But thanks for the knowledge.

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Joined: Jun 15 2014
Posts: 305
Re: Apple III main capacitor replacement question...

Samm328, the higher the voltage capacitors are rated, the better if you can physically mount (fit) them in the given room of this PSU. Don't bother with ESR, this is related to capacitors running at higher frequencies (usually tens of kHz) used in switching stages of PSUs.

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Joined: May 27 2013
Posts: 794
Re: Apple III main capacitor replacement question...

I mentioned ESR because of that thread where I learned about the safety capacitors. I posted a link to that thread but here is a quote from it:

stachowiak wrote:

...You might consider getting one of these http://r.ebay.com/SVSSLL for testing caps. It's low price and they work well for measuring ESR. It's not lab grade but will help you find bad caps that you won't find with a multimeter.

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Joined: Aug 8 2014
Posts: 42
Re: Apple III main capacitor replacement question...

I ordered the caps guys, the iii was severely damaged in shipping Sad -- I'm going to try and get the case replaced soon, a shame the machine wasn't even scratched before shipping. So right not I'm putting it to the side while I wait for shipping claims to happen.

Thanks for the cap specs, lol, you guys are a hoot.
Samm