global Laptop and motherboard repair tutorial | Page 81

Knowing how the initial failure occurred is very beneficial to helping to locate the fault. If you
know that the problem is related to a lightning storm and the power was going in and out, you can
direct the diagnosing towards the power input and leading tracks. This would include all components
on those paths, like voltage regulators, tantalum capacitors, resistors, diodes and related. Also you
would determine from the schematics sheets, the proper testing voltage/amp/current of all those
components. Let us say that that did in fact happen to the laptop in question with the fault. You would
begin by making sure the AC Adapter is properly functioning. Moving on, you would begin a visual
and audio inspection of the motherboard.
Your audio inspection:
Listening closely to a faulty motherboard will sometimes reveal the faults location, or at least
show the end result of a blown series of components.
You will sometimes be able to hear blown components making a high pitched buzzing noise, or it
will sometimes be a beeping noise, then sometimes it can also be clicking noises.
Your visual inspection:
The visual inspection is the most important part of motherboard testing. It can also be the
difference in hours of testing as opposed to directly noticing the issue.
Printed circuit boards (PCBs) are vulnerable to environmental influences; for example, the traces
are corrosion-prone and may be improperly etched leaving partial shorts, while the vias may be
insufficiently plated through or filled with solder. The traces may crack under mechanical loads, often
resulting in unreliable PCB operation. Residues of solder flux may facilitate corrosion; those of other
materials on PCBs can cause electrical leaks. Polar covalent compounds can attract moisture like
antistatic agents, forming a thin layer of conductive moisture between the traces; ionic compounds
like chlorides tend to facilitate corrosion. Alkali metal ions may migrate through plastic packaging
and influence the functioning of semiconductors. Chlorinated hydrocarbon residues may hydrolyze
and release corrosive chlorides; these are problems that occur after years. Polar molecules may
dissipate highfrequency energy, causing parasitic dielectric losses.
Above the glass transition temperature of PCBs, the resin matrix softens and becomes susceptible
contaminant diffusion. For example, polyglycols from the solder flux can enter the board and increase
its humidity intake, with corresponding deterioration of dielectric and corrosion properties.
Multilayer substrates using ceramics suffer from many of the same problems.
Conductive anodic filaments (CAFs) may grow within the boards along the fibers of the
composite material. Metal is introduced to a vulnerable surface typically from plating the vias, then
migrates in presence of ions, moisture, and electrical potential; drilling damage and poor glass-resin
bonding promotes such failures. The formation of CAFs usually begins by poor glassresin bonding; a
layer of adsorbed moisture then provides a channel through which ions and corrosion products
migrate. In presence of chloride ions, the precipitated material is atacamite; its semi-conductive
properties lead to increased current leakage, deteriorated dielectric strength, and short circuits
between traces. Absorbed glycols from flux residues aggravate the problem. The difference in
thermal expansion of the fibers and the matrix weakens the bond when the board is soldered; the lead-
free solders which require higher soldering temperatures increase the occurrence of CAFs. Besides
this, CAFs depend on absorbed humidity; below a certain threshold, they do not occur. Delamination
may occur to separate the board layers, cracking the vias and conductors to introduce pathways for
corrosive contaminants and migration of conductive species.
A lighted magnifying glass or better yet a microscope would help you with the visual inspection
to bring your field of view up close and allowing you to look for faults. You can buy a headset