At 10:15 -0700 10/5/05, Scott Baret wrote: >Does anyone have a theory as to why all the capacitors >on Mac II series computers seem to have problems?
Electrolytic capacitors have been a significant failure point for essentially all electronics built in the 70's and 80's. It's curious that much older capacitors, from the 50's, are still working. I suspect, but can't prove, that the drive to miniaturization led to manufacturing shortcuts that should be reviewed in hindsight. Aluminum electrolytics are full of acid. It's what creates the very thin layer of aluminum oxide that is the dielectric. They leak, dry out, and then fail. Tantalum electrolytic capacitors that use a solid tantalum sponge-like structure were slow to be perfected but are now a much better replacement for long life systems. But when you look at current manufacturer's specifications you find MTBF for both types given in hours at maximum rated temperature. Electrolytic capacitors like to be stored with voltage on them. It's an electrolysis process, similar to that used for anodizing aluminum drinking cups, that creates the oxide dielectric. In the absence of a bias voltage the dielectric slowly dissolves into the acid. Very old capacitors can often be rejuvenated by applying a bias voltage for a few days. Old Mac's sitting on a shelf are more likely to have problems than Mac's recently removed from service. -- --> 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. <-- -- Vintage Macs is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Enter To Win A | -- Canon PowerShot Digital Cameras start at $299 | Free iBook! | Support Low End Mac <http://lowendmac.com/lists/support.html> Vintage Macs list info: <http://lowendmac.com/lists/vintagemacs.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/vintage.macs%40mail.maclaunch.com/> iPod Accessories for Less at 1-800-iPOD.COM Fast Delivery, Low Price, Good Deal www.1800ipod.com
