Disclaimer - This is a tutorial and is not a substitute for
a formal Tech repair class that will teach you the art of troubleshooting,
soldering, and general safety. This web site and the owner are not responsible
for any damage you may do by following these techniques.
A motherboard has all the support chips for the operation
of the processor.
Simple to say, how hard to explain?
Hard –
So let’s simplify the motherboard down to some components.
They are:
Processor
Memory
Support chips
Clock chips
Crystals
I/O chips
Keyboard
Serial port (includes the USB chips)
Parallel ports
Video (embedded)
Sound (embedded)
NIC Wired (embedded)
NIC Wireless (embedded)
Ports for the above chips
Power supply circuits
Slots
Resistors, caps, transistors
The copper wires you see are called a traces (the thin
copper that is etched on to the PCB)
Now let’s look at the make up of the physical properties of
the motherboard.
Modern motherboards are made up of layers, some up to
fifteen layers (high end servers and workstations). Each layer of PCB (Printed
Circuit Board) starting from the lowest or bottom layer has a series of traces,
then the next layer of PCB with a series of traces, then the next layer of PCB
with traces, and so on to the top layer. Once all the layers of the motherboard
have the traces then each one is precision drilled for the pass through that are
pressed in the completed motherboard. Then all the layers are stacked and a
process (some are proprietary) is used to compress and bind all the layers
together. Then all the pass through are pressed in the holes that were drilled
earlier in the process. Some motherboards have layers that the pass through is
put in before final assembly because they on go through two to more layers but
not all. Once this process is complete then the motherboard is sealed.
The next step is to bind or solder all the components on
the mother board, the smaller components such as support chips, resistors, caps,
transistors (yes they still use transistors), and diodes. The process uses wave
soldering where the motherboard is subjected to liquid solder that adheres to
the bare copper where the sealant is replaced with solder flux. then the next
step is putting on all the micro components such as the list above, this is done
with robots that do what is called pick-and-place, then the solder under the
component is melted and the component is secured. The next step is non micro
components such as the processor socket, the memory slots, add on card slots,
the peripheral connectors (IDE, SATA, Floppy Drive, external connectors for
keyboard, network, usb, sound, and firewire) and so on. Also any other items
such as caps, switches, and other items.
The motherboard is complete, next the motherboard is
tested, some manufactures use a jig that the memory, processor, and the
peripherals are all simulated. Other manufactures use actual components to test
the motherboard. The motherboard is connected up to a test station then powered
up. How long and how rigorous the motherboard is depends on the manufacture. The
main thing is that the more rigorous the testing the less returns from dead on
arrival (DOA) when the motherboards are sold.
Now you want to repair your motherboard.
Ok, do you have the following tools –
Low wattage soldering iron (max twenty-five watts)
Small tips for the soldering iron (as small as 1/16th
of an inch)
Heavy duty heat sink (Must absorb up to 300 degrees F)
A good magnifying glass
A strong light
Various electronics tweezers (angled and straight,
spring loaded open or closed)
Desoldering vacuum
Desoldering copper weave
Now do you have the experience using the above list?
Any one can learn how to solder, takes a little practice to
keep from melting the component and burning your fingers. What I am talking about
is recognizing when the solder starts to melt, removing the heat and the
component at the same time. Then heating the solder to the point where you can
put the new component back with out destroying it?
Here is something a lot of people don’t know – the
motherboard will start to degenerate when the temperature reaches 325 degrees F.
That is the binding that the manufacture used when the motherboard layers were
pressed together will start to separate, if the separation happens to be where
there is a pass though then the motherboard is effectively destroyed. That is
the reason for the heat sink that will absorb the heat that will spread while
you are soldering.
If you are replacing a large component such as a cap or a
resistor or a socket then it is fairly easy. Just keep the heat from building up
and causing the layers or traces from separating. But the small components are
the hard part.
To remove a micro resistor or cap then you have to insure
that the heat stays local to the spot you are working on. You only apply the
heat to the failed component, and this is important, you only heat an area
twice. Once to remove the failed component and once to solder the new component.
That takes care of the easy part. You know the component
failed by seeing it is brunt, or in the case of a bad cap it exploded. Or you
did a test and found the failed component by lack of voltage or resistance.
Now comes the hard parts-
How do you repair a trace that has lifted from the
motherboard? Answer: You can’t, once the trace lifts the only thing you can do
is to by pass the part that has lifted with a thin gage insulated wire.
You would do this by finding two points where the trace is
wide enough to accommodate the small gage wire. I will warn you do not use a
pass through to put the wire in. Why? The heat that the solder will produce will
cause the pass through to separate from the traces inside the
motherboard, may
even cause the motherboard to ‘bubble’ around the pass through. You would use an Exacto knife or thin razor blade knife to careful scrape off the sealant. Cut
the bad trace just past the places where you scraped of the sealant. Heat and
apply solder to both ends of the wire only. Once the wire is tined then put one
end of the wire on the scrapped trace and apply heat – just long enough to melt
the solder, be careful with the heat the trace is all ready exposed and will not
take much to separate it from the spot where the sealant has been removed. Solder both ends, then test the repair with an ohm meter. If it tests good then
use some fingernail polish to reseal the solder points.
You can do low level component repair but I will warn you
that a component failure do to the component material failure is low. Something
caused that component to fail, heat, voltage, or amperage above the component’s
design specifications. You need to test further upstream before completing your
repair or you will either have a lot of smoke or a fire.
Good luck with doing your low level component repair.
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