Thank you Doug! NOW it makes some sense as to why cleaning the board of residue might restore funtionality - because the cap may be unaffected! So much time is given to this topic, yet the basics are often overlooked. I am ignorant of this topic in a scientific way, so a simple explantion like this really clicks. ATTA BOY!
Rich Bennet --- Doug McNutt <[EMAIL PROTECTED]> wrote: > At 17:43 +0100 7/4/05, Sean Billings wrote: > >And another thing! There was mention on this > thread I think about why > >capacitors fail, pointing to a finite life etc. > could it also not be that > >the extended periods of inactivity these machines > went through before being > >'rescued' by people like ourselves could contribute > to the failure? > > Aluminum electrolytic capacitors are made from two > layers of aluminum foil that are separated by an > insulator made of porous "paper" saturated with an > acid - it was once sulfuric or chromic acid but the > choice is proprietary. > > After the capacitor is made it has its electrodes > formed by applying a DC voltage that is slowly > increased. The process makes current flow and the > anode aluminum oxidizes to form an insulating layer > of Al2O3 which increases in thickness during the > forming process. It is that very thin layer of oxide > that is the insulator that makes the aluminum plates > be a capacitor. The remaining acid is just a > conductor. > > When capacitors like that dry out the thickness of > the insulator becomes large and the capacity gets > smaller such a capacitor is trash. When they are > left for a long time without a DC biasing voltage > the oxide can de-dissolve into the electrolyte. In > some cases slow application of increasing voltage > can reform such a capacitor but that's hard to do > in-circuit because there is no way to start with a > reduced voltage. The failure being seen in classic > Macs is a simple leak of electrolyte which doesn't > affect the capacitor very much but it raises hell > with the printed circuit board underneath. The > capacitors leak because they were cheaply made with > insufficient testing of the design. > > -- > --> On the eighth day, about 6 kiloyears ago, the > Lord realized that free will would make man ask what > existed before the Creation. So He installed a few > gigayears of history complete with a big bang and a > fossilized record of evolution. <-- > > -- > Compact Macs is sponsored by > <http://lowendmac.com/>. > > Support Low End Mac > <http://lowendmac.com/lists/support.html> > > Compact Macs list info: > <http://lowendmac.com/lists/compact.shtml> > --> AOL users, remove "mailto:"; > Send list messages to: > <mailto:[email protected]> > To unsubscribe, email: > <mailto:[EMAIL PROTECTED]> > For digest mode, email: > <mailto:[EMAIL PROTECTED]> > Subscription questions: > <mailto:[EMAIL PROTECTED]> > Archive:<http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/> > > > --------------------------------------------------------------- > iPod Accessories for Less > at 1-800-iPOD.COM > Fast Delivery, Low Price, Good Deal > www.1800ipod.com > --------------------------------------------------------------- > -- Compact Macs is sponsored by <http://lowendmac.com/>. Support Low End Mac <http://lowendmac.com/lists/support.html> Compact Macs list info: <http://lowendmac.com/lists/compact.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[email protected]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive:<http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/> --------------------------------------------------------------- iPod Accessories for Less at 1-800-iPOD.COM Fast Delivery, Low Price, Good Deal www.1800ipod.com ---------------------------------------------------------------
