Re: Apple //e Power Supplies

[quadrajet1@aol.com (Quadrajet1)]

>I dunno about a design flaw, but any electrolytic capacitor has a life
>expectancy of about 10 years unless it is an expensive high-grade type.
>Switching power supplies such as those used in the Apple II can generally
>be expected to fail after perhaps 15 years due to electrolytic capacitor
>degradation. Fortunately, they are easy to fix, all you have to do is
>replace the electrolytic capacitors and it will be as good as new.
>
>You can go to the trouble of getting exact replacements for the caps, but
>a good rule of thumb is to use caps within maybe 10%-15% of the capacitance
>and the same or higher voltage rating. Be aware that modern caps are a LOT
>smaller physically than caps of the same rating from 20 years ago!
>
>If the cap you mention is under-rated for its environment, then that is
>indeed a design flaw, and that cap should be uprated in both temperature
>and voltage ratings (to some extent it is the same thing.)
>
>Tom Zuchowski
>

   I call it a design flaw because the power supplies were failing after 2
years or less, and they mounted an electrolytic cap right next to (less than
1/4" away) a big ole' power resistor that was notorious for staying hot.  So
the cap failed prematurely from being baked by the resistor.  Had they mounted
the cap and resistor farther from each other, the failure wouldn't have
occured.  There was the same design flaw in the power supply in the Apple Duo
Dock power supply.  Seems 90% of the Duo Dock power supplies can be repaired by
replacing a cap that was mounted within a quarter-inch of a power resistor that
baked the cap, drying it out.  Same design flaw in the Mac IIci/cx power supply
too.  

  On the Mac IIci, the power resistor stayed hot whenever the power supply was
plugged in, not neccesarily powered up.  The power supply got to a point where
it wouldn't start up.  Unplug the power supply, let the cap cool down, then it
would start up.   So in these 3 instances, the power supplies failed just at
the 2 year mark or slightly more.  So I call it a flaw in component placement. 
When I rebuilt a Apple II power supply with this problem, I put the cap farther
away from the resistor, so it wouldn't fail anytime soon.

>"Quadrajet1" <quadrajet1@aol.com> wrote in message
>20010223020118.02994.00002350@ng-cs1.aol.com">news:20010223020118.02994.00002350@ng-cs1.aol.com...
>>
>>     Basically the power supples were made by either Dyna-Comp or Astec. The
>> longer power supplies supplied a higher current rating than did the shorter
>> ones.  I prefer the Astec power supplies any day, but the older ][+ power
>> supplies had a bad design flaw that caused a cap to fail.
>>
>> Raymond