Path: news.uiowa.edu!news.uiowa.edu!uunet!in1.uu.net!newsfeed.internetmci.com!tank.news.pipex.net!pipex!dispatch.news.demon.net!demon!mail2news.demon.co.uk!toshibai.demon.co.uk From: Mike Smith Newsgroups: comp.sys.apple2 Subject: Re: Power supply for Apple GDSII Date: Tue, 29 Aug 1995 08:44:50 GMT Organization: None Lines: 16 Message-ID: <479083031wnr@toshibai.demon.co.uk> References: <817049950wnr@toshibai.demon.co.uk> Reply-To: mikes@toshibai.demon.co.uk X-NNTP-Posting-Host: toshibai.demon.co.uk X-Broken-Date: Tuesday, Aug 29, 1995 08.44.50 X-Newsreader: Newswin Alpha 0.7 David, thank you for the reply. I found the problem this weekend, there was a 100k bias resistor in the front end of the inverter. The resistor was open circuit. Sympton was that one of the elctrolytic capacitors was at 260 volt & the other was at 30 volt. When running correctly they are both at same voltage ( approx 140 volt) and within the 200 volt working rating of the capacitor. For information, from my memory, its a 6 pin molex type connector. Thank you for your comment. -- Best Regards,Mike Smith=========== Bill Garber wrote: >I don't mean to sound insulting, but why isn't anyone >suggesting checking of fuses. That is the first place I'd >look. Also in most power supplies there is a rather large >resistor in the line between the AC cord and the main >transformer. Another fault could be the main capacitor >just after the transformer. The Apple ][ supply is a switching power supply, so there is no transformer on the line side of the supply. There is an internal fuse, then a half-wave voltage doubler, and then the switcher. Usually when the fuse blows, it means a capacitor or a switching transistor, or both, are shorted, so replacing the fuse has a low probability of success. The most common cause of old Apple supplies failing is loss of capacitance or increase of equivalent series resistance of one or both of the capacitors in the voltage doubler. If they go too far out of spec, the supply will not start under load. If you are justifiably confident of your ability to repair a supply, try replacing the capacitors with ones scavenged from old one-time-use flash cameras--they have 330+ volt ratings and are about 100 microfarad or so, so should do the job nicely. -michael Check out amazing quality 8-bit Apple sound on my Home page: http://members.aol.com/MJMahon/