Path: news1.icaen!news.uiowa.edu!news.physics.uiowa.edu!newsrelay.iastate.edu!vixen.cso.uiuc.edu!howland.erols.net!news2.digex.net!digex!swbell!not-for-mail From: Rubywand Newsgroups: comp.sys.apple2 Subject: Re: Power supplies Date: Wed, 08 Oct 1997 17:37:51 +0000 Organization: Southwestern Bell Internet Services, Richardson, TX Lines: 136 Message-ID: <343BC4EF.7019@swbell.net> References: <97281.113842JCA31@MAINE.MAINE.EDU> NNTP-Posting-Host: ppp-207-193-16-54.hstntx.swbell.net Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Trace: nnrp1.rcsntx.swbell.net 876353636 3807 (None) 207.193.16.54 X-Complaints-To: usenet@nnrp1.rcsntx.swbell.net X-Mailer: Mozilla 2.02E (Win16; I) JCA31@MAINE.MAINE.EDU writes ... > > I now have in my posession several II's that have dead power supplies. > .... > > Since they all seem to be the same design, and about the same age, i'm > suspicious that there's something that typically goes wrong in these > beasties. If anyone can provide hints on what that might be, not only > could i repair the supplies (and thus the machines) i do have, but when > the others inevitably go, it won't be an irreversible loss. > .... Maybe my earlier email got lost; so, just in case, below is a kind of general purpose fix-it guide ... First, it's a good idea to check for shorting caused by Coke spills etc. Open the case and look for gunk on the motherboard and power supply. If everything looks okay, fine. If not clean away the mess. After cleaning (and drying), turn ON the power to see if the problem is fixed. Bad or Cross-socketed Slot Card Pull all cards from Slots and turn ON power. If the machine 'comes alive' one or more of your cards may have a short or may have been cross-socketed. Clean the contacts on each card (e.g. with alcohol). With power OFF, replug a card (be sure to line-up card and Slot contacts) and turn ON power. Do this for each card. If a card causes the machine to fail, it is, probably messed up. If no card produces a failure the original problem was, likely, a card which was not properly inserted. Bad Power Cord Unplug and replug the power cord at the point where it connects to the IIe. Turn ON power. Try wiggling the power cord. If the Power Supply comes ON at any time, try substituting a power cord from a known-working IIe. If this fixes the problem, you can be pretty sure that the problem was a power cord with a broken wire. Poor Power Supply Connector Connection Unplug and re-plug the Power Supply cable to the motherboard. Turn ON power. If the machine seems to respond, or responds when the connector is wiggled, you probably have a dirty or loose connection. Clean the power supply plug and socket with an alcohol swab. Using long-nosed pliers slightly re-crimp the 'holes' on the socket (or, insert a jewler's screwdriver into the space between each hole and the plastic casing and twist). The idea is to restore a firm grip for all contacts. Another possibility is a loose or broken socket solder connection to the motherboard. The repair is to remove the motherboard and re-solder the connections to the socket. Bad Switch It is fairly easy to identify a bad switch-- it will, usually, not snap cleanly into position, feel crunchy, and/or have a burn spot. The repair is to replace the switch with some AC power switch that will fit. Or, you can permanently connect the switched lines and add an in-line switch to the power cord. Blown Fuse Some power supplies may have a fuse. Open the power supply. Look for a fuse mounted to the circuit board. If there is one, check it. An Ohm meter can be used to check for continuity if it is not obvious that the fuse is blown. If the fuse is blown, replace it. Bad "Globar" Element Look toward the end where the power cord is connected. Somewhere close to the place where wires from the switch go to the circuit board there should be a small disk-shaped component which is not a disk capacitor. Probably, it will be black with no markings. This is a "globar" resistor. Check it to be sure that it is not cracked and that both leads are really connected to the disk. If the globar element is broken or if a lead has popped off, you will need to get a replacement from an electronics supply shop. (Tell the shop person where the globar resister comes from and describe its size.) Blown Electrolytic Capacitor(s) On the end of the circuit board near the Switch are some relatively large electrolytic capacitors (typically these are tubular aluminum things with shrink-wrapped grey or light-green covers on which there are markings). Usually, they are the same size and have the same uF value and Voltage rating. One (or more) of these may be obviously blown or may just show some slime near the base. If you find something like this, the suspect capacitor should be replaced by one of the same (or slightly larger) uF value with the same (or larger) Voltage rating. Size and shape are, also, important in order to get a good fit. When removing the bad cap, be sure to mark the "+" side on the board-- use the markings on the cap's cover to identify the "+" side. Install the replacement cap with its "+" lead in the marked hole. Messed-up or 'Dirty' Adjustment The power supply may have a mini-potentiometer mounted on the circuit board for fine-tuning voltage output. Usually, it will be somewhere near the end opposite the Switch and will have a slotted plastic 'knob'. If there is such an adjustment, mark its current position and, then, turn it back and forth. (If you have some Radio Shack, etc. 'Circuit Cleaner', into the mini-pot first is a good idea.) Set the adjustment a bit to one side of the original setting and plug in the power supply. If it now seems to work the problem was a 'dirty' voltage adjustment control. Check the voltage on the +5V line with a meter and adjust it to 5 Volts. (Note: _no_ output due to a dirty adjustment control seems unlikely. Incorrect output is more probable; and, this could cause a IIe to not work.) Beyond the above, you are, most likely, looking at a bombed electrolytic capacitor which is not obviously bad or a blown main power transistor (the big silvery thing mounted on a heatsink). Unless you enjoy more involved electronic testing and repair work, your best course is, probably, to get a replacement power supply. Rubywand