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From: Rubywand <rubywand@swbell.net>
Newsgroups: comp.sys.apple2
Subject: Re: Power supplies
Date: Wed, 08 Oct 1997 17:37:51 +0000
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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