Path: blue.weeg.uiowa.edu!news.uiowa.edu!hobbes.physics.uiowa.edu!math.ohio-state.edu!usc!howland.reston.ans.net!agate!msuinfo!harbinger.cc.monash.edu.au!news.cs.su.oz.au!metro!ob1.uws.edu.au!lancelot.st.nepean.uws.edu.au!adrianw From: adrianw@guinevere.st.nepean.uws.edu.au (Adrian Whichello) Newsgroups: comp.sys.apple2 Subject: Re: Apple II+ power supply woes Date: 13 Aug 1994 17:09:31 +1000 Organization: University of Western Sydney Lines: 40 Message-ID: References: NNTP-Posting-Host: 137.154.148.15 Keywords: power supply woes adrianw@kay.st.nepean.uws.edu.au (Adrian Whichello) writes: >Hi Netland >I have an old 2+ which runs the model railway, among other things. >Last week it's power supply gave up. I wasn't there at the time, >I've found that leaving the computer permanently switched on is >good insurance - the power supplies tend to die between cycles if >eft off for long periods. Anyway, I opened it up and found that >an electrolytic had swelled up so much that it had torn it's connections >out of the circuit board. I replaced it, but all the power supply >wants to do now is go click click click ie it won't oscillate >properly. It does this if plugged into the motherboard or not. >Any suggestions about what else could be wrong. I'm not wild >about diving into a circuit that is connected directly to the >house supply without some clues. >Adrian. >ps surely this must be a FAQ by now - I have several old supplies >that are dead for one reason or another. Hi Netland had a go at the power supply over the weekend. I was successful, because I typed this on the Apple. There was nothing wrong with the bridge rectifier and input side - there was over 300V on the collector of the big transistor. None of the inductors had burnt out and all the diodes and transistors checked out OK with a simple multimeter check. In fact nothing looked wrong at all, physically. There was just hardly any (~0.5VDC) voltage on the output side. I was getting desperate! I decided to check out the voltage reference section - I faked 5VDC (from the bench power supply) on the anode of the TL-431C and up came the power! So then the penny dropped, the capacitor the temporarily shorts out the 4.7K 1% resistor at power on wasn't doing it's job. I replaced it and away we went, all systems go. Anyone else found this? Adrian.