17.010 What are some good Apple II power supply fix tries?
Description
This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
17.010 What are some good Apple II power supply fix tries?
Apple II power supplies can often be repaired. The bother involved varies
considerably with the cause of malfunction.
Note: The following refers more or less directly to II+ and IIe supplies;
however, many of the ideas will work with the IIgs power supply as well.
Note: Unless otherwise indicated, power should be turned OFF.
A Short
Open the case and check inside for indications of Coke spills, debris,
etc.. If everything looks okay, continue on. If not clean away the mess; it
could be causing a short. After cleaning (and drying), turn ON the power to see
if the problem is fixed.
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
jeweler'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 resistor 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.
Note: Also see the fix in the next Q&A and the C7 fix discussion in Q&A 012.
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, a blown resistor (which may be easier to
spot), 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.
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