Since Apple Corp. has stopped supporting the Apple2, it has become increasingly
hard to find places where Apple2's can be repaired. Such repairs have also become
increasingly more costly. One solution, other than scrapping our beloved
machines, is to learn to repair them ourselves. In most cases this is much
simpler that may sound. Here, a method will be presented which usually fixes a
dead Apple about 95% of the time. It will be called "the method of chip
comparison."
There are two requirements for this method. One is that the chips (IC's or
Integrated Circuits) to be compared be socketed. That is, they must be readily
removaable from their circuit boards. Sometimes chips are soldered directly to
their circuit boards. Such chips will be considered later.
The second requisite for the method of chip substitution is that you must have
access to another working Apple2 of the same type and model. You cannot repair a
non-functional Apple II+ if you only have a working Apple IIe with which to
compare it.
The process is extremely simple.
1. Remove a chip from the working Apple. Set it aside carefully.
2. Replace it with its counterpart from the dead Apple.
3. Check to see if the formerly working Apple still works.
a. If it doesn't, you have found a dead chip. Replace it with
a good chip in the non-working Apple and see if it works.
i) If it does, replace the original chip in the
originally working Apple and celebrate.
ii) If not, replace the original chip from the original
Apple back in the working Apple and choose another
pair of equivalent chips to test the same way.
b. If it does, replace the chip into the dead Apple, put back
the chip taken from the originally working Apple and choose
another pair of equivalent chips to test the same way.
You must be very careful to align the notch or other marker on the end of a chip
with the corresponding notch or marker on its socket. A chip put in backwards may
not only blow itself but may also badly damage the rest of the computer. Also, be
very careful to remove the chip from its socket, and notremove the socket from
the circuit board. When inserting chips into sockets,make sure that all the pins
are straight and properly aligned with their recepticles on the socket.
Most of the chips (the little ones) will be "74xxx" series chips. These
are very
easy to obtain from most electronic stores or catalogs. They usually cost from
pennies to a few dollars. Some of the larger broader chips, those marked "APPLE",
are proprietary chips made especially for Apple. Such chips cost more since Apple
controls their production and distribution. Nevertheless they may be obtained
from such sources as Alltech or Shreve Systems. They cost anywhere from $10 to
$30. (But Apple repair technicians charge $85 per hour plus inflated costs of
parts!)
To check chips which are soldered to circuit boards, they must be desoldered and
socketed. The older chips whose pins project through the circuit board may be
quite easily desoldered and socketed with the directions below. However, there is
a more recent technology consisting of "surface mounted chips". These are
found
in machines such as the IIgs, and in 3.5" disk drives. To desolder or check
these
requires special (i.e. expensive) tools and measurement equipment. We will not
deal with surface mounted chips here.
Each pin which projects through a circuit board is fitted into a copper grommet
which goes through the circuit board. These grommets are filled with solder which
also adheres to the chip pin, making firm electrical and mechanical contact. To
remove the solder, there are two methods. The easiest is to use a
"solder-sucker". This is a little rubber bulb with a heat resistant teflon
nozzle
at its end. The nozzle is placed over the protruding part of the pin at the back
(non-component side) of the board. The bulb is held squeezed. The hot soldering
iron is placed against the base of the solder joint on the other (component) side
of the board and the solder in the grommet melted. Then the bulb is suddenly
released, sucking the molten solder out of the connection. (If any solder sticks
in the nozzle, it may be poked into the bulb with a bent paper clip.)
This desoldering method is gentlest, but it presumes that the components are far
enough apart to place a soldering iron at the base of the pins without melting
anything but the solder in the joint. When this is not the case, one must use
"desoldering braid". This is a braid made of very fine copper wires. (Desoldering
braid and a desoldering bulb are obtainable at Radio Shack.) The principle here
is that of a paper towel sucking up liquid out of a small hole by capillary
action. Just in this case we have to melt the solder and hold the hot braid
against it simultaneously. To ensure that the solder "wets" the braid,
dip the
braid in soldering paste. (Use the paste or flux from an electronics supply
house, NOT a hardware store! Plumbing flux is acidic and will destroy circuit
boards.) Press the fluxed braid against the joint to be desoldered, using the tip
of the hot soldering iron. Thoroughly melt the solder in the joint for the braid
to soak-up. Cut off the end part of the braid which is full of solder, and use
fresh fluxed braid for the next joint.
A properly desoldered joint should show light through it when looking at a light
source. If it does not, cut the tip of the desoldering braid to a point, and
insert the fluxed point, applying heat to melt the residual solder so it too is
absorbed by the braid.
Before trying to lift the chip from its board, you must break its pins from the
sides of their grommets. Do this by applying pressure from the top with the
corner of a flat screwdriver. Considerable pressure is sometimes required. You
should feel the end of the pin, the other side of the board, move a little
against a strategically located finger tip. Next, grab the end of each pin with a
needle nosed pliers and wiggle that end until it is free. Repeat this until all
pins are free. Now the chip should lift off the board with only the gentlest
force. BE SURE NO COPPER TRACES LIFT FROM THE BOARD WHEN
REMOVING A CHIP!
Clean the board with swabs of cotton soaked in rubbing alcohol, and straighten
the pins of the chips which were removed. Sockets (obtainable from Radio Shack
and other electronic stores and catalogs) may now be put into the empty spaces on
a circuit board and soldered in place of the chips. Make sure that each socket is
properly aligned with its notch in the same direction as the white indicator
marks on the board. (Those white marks outlining components are called "silk
screening".) also make sure the sockets are flush against the circuit board
with
ALL their pins projecting through. Apply the tip of the soldering iron to the end
of the socket pin projecting out of the back of the board, and touch the hot
joint with some solder. (I use the fine silver bearing (2%) solder from Radio
Shack.) It should fill the joint without overflowing either end of the grommet.
Again, clean the board up with cotton swabs soaked in alcohol. (I use a
toothbrush to get rid of all the adhering cotton fibers afterwards.) Place the
removed chip into the new socket and treat it as any other socketed chip.
If all this sounds too complicated and scary to try on your beloved Apple's logic
board, get an old PC board and PRACTISE. A modest amount of effort should make
you competent to try the real thing!
The preceeding techniques and methods may be applied not simply to mai logic
boards of Apples, but also to the analog boards of 5.25" disk drives, and to
all
those lovely cards which fit into our beloved Apple2 slots. Reaching even farther
afield, all equipment having socketed or socketable chips may be repaired by this
method. Approximately 95% of the reasons why computers fail are traceable to chip
failures.
The remaining problems are usually very specific to the type or piece of
equipment being repaired. For example, the video jack on a IIe sometimes breaks
off from its inner connection with the main logic board. If this is the case,
simply repair it with a little solder. The metal case of the internal disk drive
of a IIc sometimes shorts to a transistor on the logic board beneath it. A piece
of paper between the disk drive case and the main logic board will solve this
problem. The ribbon cable on a disk drive sometimes has snapped conductors. This
often occurs at the place it enters the computer case. It is especially
vulnerable where the cable is grasped by a grounding clip on a IIe or II+. Fix or
replace the cable. (You can test the cable against that of a working disk drive
just like the chips were compared.)
Good luck with repairing your own machines!
Standard disclaimer applies (anyone following advice given here does so
at her/his own risk).