on 10/5/05 1:49 PM, Doug McNutt at [EMAIL PROTECTED] wrote: > 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.
Capacitors on paper such as in electrical engineering classes are ideal devices. But in reality they are are practical real-world devices. They've come along along way in the past 50 years but are still not perfect. Ask your favorite guitar, bass or harmonica player what are the main problems they have using their preferred vintage 50's or 60's amplifiers and they'll tell you right away that they've had to have all the capacitors replaced (in addition to the tubes). It's the nature of the beast. Semiconductors (IC's) don't have this problem since they are monolithic but caps are a thorn in the side. This is true in every branch of electronics. Caps, such as those in cell phones, now come in varieties that are 1mm x 2mm but over time they'll have that problem too. The issues will certainly be different but similar in nature. Invent the perfect capacitor and you too will become a zillionaire. Rick -- 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:vintage.macs@mail.maclaunch.com> 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
