Path: blue.weeg.uiowa.edu!news.uiowa.edu!uunet!tcsi.tcs.com!agate!msuinfo!harbinger.cc.monash.edu.au!yarrina.connect.com.au!werple.apana.org.au!boombox.apana.org.au!tlp!peterm From: peterm@tlp.apana.org.au (Peter Maloney) Newsgroups: comp.sys.apple2 Subject: Re: IIe power supply problems Message-ID: Date: Fri, 02 Sep 94 16:53:18 PDT References: <1994Aug31.162618.1101@sandia.gov> Organization: The Lower Planes BBS Lines: 45 kjhass@sandia.gov (Joe Hass) writes: > > Wizards of the Net: > > I'm trying to help a local elementary school keep their IIe's running and > have found what appears to be a bad power supply. > > The machine will boot properly when it's warm but the power supply won't > come up if it's cool. When it's cool the +5 output is at about 1.1V, the > -5 is at about -1.1V and the +/- 12V outputs are proportionately low. > Sometimes, if it's not too cool, the voltages will slowly rise and then > the supply will suddenly come to life and be fine. I know it's the supply > and not the motherboard because I've swapped them with another machine, > and I've tried heating the supply alone with a hair dryer. Also, when the > supply is cool but disconnected from the motherboard the positive voltages > are about 1% above nominal and the negative voltages are about 10% more > positive than nominal. > > I can't see any cold solder joints or obviously bad components. The > machine is of 1985 vintage and the supply was made by Astech. > > Any diagnostic suggestions would be appreciated, as well as pointers to > a low-cost vendor for a new supply. I'm an EE so I have a passing > familiarity with switching power supplies, but I don't have the schematics > for this guy. > > TIA, > Joe > > -- > Joe Hass | library clever_sigs; | My opinions are my o > kjhass@sandia.gov | use rock_and_roll.verses.ALL; | not Sandia's and > Sandia National Labs | use lineprinter.art.ALL; | not the DOE's Theis problem is usually caused by a failed capacitor (220uf/16V?) that sits near the big power transistor. Test it by warming it up before you power on. Regds, Peter M. peterm@tlp.apana.org.au TLP - The only *REAL* A2 BBS in Peter Maloney Melbourne A2 Hardware Freak Path: blue.weeg.uiowa.edu!news.uiowa.edu!hobbes.physics.uiowa.edu!math.ohio-state.edu!usc!bloom-beacon.mit.edu!senator-bedfellow.mit.edu!pbauer From: pbauer@ATHENA.MIT.EDU (Paul H Bauer) Newsgroups: comp.sys.apple2 Subject: Apple II Power Supplies Date: 28 Nov 1994 04:09:04 GMT Organization: Massachusetts Institute of Technology Lines: 21 Message-ID: <3bbl50$2lj@senator-bedfellow.MIT.EDU> NNTP-Posting-Host: puttanesca.mit.edu For those of you that have had power supply problems! This week-end I descided to clean up my work bench and either repair or throw out a few AII power supplies I had in various states of disrepair. I made an interesting discovery on two supplies, one an aztec (?) unit, and the other a dead unit from a late model platinum 2e. The supply from the platinum unit was dead. After checking almost all of the semi-conductors and finding them good I finally started looking at the resistors and found a 100k 1 watt unit that kick starts the supply was open. Replacing this resistor fixed the supply. I then looked at the aztec unit. This unit woul sometimes start but most of the time it would not. I looked at the same resister (R3) which is a 150k 1 watt resister. I changed this to a 100k 1 watt unit and the supply works like a champ. If you have a dead supply you might check these resisters as they could be the culprit. The resister goes from the + rectified line side to low voltage oscillator that drives the power switching transistor. pbauer@mit.edu