From: James Wages (james_at_kiramek.com)
Date: Thu Dec 29 2005 - 22:23:16 PST
On 12/30/05 11:53 AM, Andrei Chichak <newton_at_chichak.ca> wrote:
> Electrolytic capacitors do dry out...
From an "observer's" standpoint, the above statement is correct. However,
oil in capacitors doesn't vaporize into the air (i.e., "dry out"). Evidence
of this is in your own kitchen. If oil vaporized as water, you would have
nothing to clean but dust around the stove. Sadly, that oil likes to
literally "stick" around!
In most cases, the oil leaks out onto the logic board. It may be very hard
to spot, especially if there is not dust stuck in it. I had this problem on
an SE/30 motherboard, where I was getting SimasiMac (horizontal stripes at
bootup).
Many fellow Mac users advised me to simply place the SE/30 board in the
washing machine; but since we lack such machines here in Japan, I resorted
to cleaning by hand with alcohol. Of course, mere cleaning is only good to
prevent shorting caused by the leaked oil. The next important step is to
desolder your electrolytics and put new ones in place.
So long as the Farad capacitance value is the same, and the voltage rating
is the same, you are good to go regardless if the capacitor is of the
original SMD type. I replaced all the electrolytics on my SE/30 motherboard
because they all were of the same SMD type that could go bad at any time.
That made all the difference in the world, and after booting with the new
caps, my stripes were gone.
In many cases, you may not know there is a problem until you add something
that draws extra power from the machine you are using. In my case, the
stripes appeared after adding a PDS card. The card draws more power through
the motherboard. Since the electrolytics are on the motherboard to keep the
chip voltage levels from falling, a dead cap or two would allow the voltage
to fall and cause system instability. So I believe a lot of old equipment
may have problems with leaked oil caps, but in most cases the end user can
never tell because the voltage level on the chips is stable enough to where
the caps really aren't needed. Your mileage may vary.
Some people say you can use Tantalum or Mylar replacements for
electrolytics, which I suppose is true for most designs. But one must
consider that there are mylar, tantalum, ceramic disk and electrolytic type
capacitors all on the same board sometimes. Each has different properties,
and it is not always "cost" that determines the design. Sometimes you would
want to use an electrolytic over another type. So unless you understand
what type is needed in a particular design, replace with the same type
capacitor.
Best,
James Wages
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