Early motherboards used a split power connector with
a single row of pins. The cable from the power supply had two connectors that
could easily be connected incorrectly. Technicians needed to remember to place
the connectors with the black wires together.
Power connectors
from the PC, XT, and AT motherboards
Starting with ATX motherboards, a
keyed two-row connector was used. The socket on the motherboard may have 20 or
24 pins, depending on power requirements. Power supplies provide a 20-pin plug
and a 4-pin plug to accommodate either motherboard socket type. The plugs from
the power supply can be attached to form a single 24-pin connector. Some
motherboards also require extra power for the CPU via a separate 4-pin
connector.
Motherboard power connector (20 and 24 pins) and CPU
power.
Some PCI-Express video cards require extra power via six or
eight-pin PCI-E power connectors. If such a video system is integrated into the
motherboard, these connectors are on the motherboard.
PCI-E power
connectors
Battery
The motherboard battery powers the real-time
clock when the power is removed. This was also used to power the CMOS memory
chip that stores the computer's configuration, which is now stored in flash
memory. Early motherboards had soldered-in rechargeable batteries (see below), but virtually
all motherboards now use CR-2032 button cells.
A CR-2032 battery used
on most motherboards.
Early motherboards often used nickel-cadmium (Ni-Cd) batteries. These
batteries recharged when the power was on and held enough charge to power the
CMOS chip as long as necessary when the power was off. Ni-Cd batteries often
leaked when they aged, damaging the motherboard. Some motherboards had a pair of
pins to which replacement alkaline batteries could be attached.
Other factors
Electrolytic Capacitors
Aluminum-foil electrolytic capacitors are filled with water and boric acid
electrolyte. Very old electrolytic capacitors tend to have a limited life span
of 20 to 30 years. Starting about 1998, many electrolytic capacitors were
manufactured in Taiwan with a defective electrolytic formula. These capacitors
tend to fail after only about three years. When the capacitors fail, they
sometimes explode, but more-often bulge and then leak at the pressure relief
vents on top. Theoretically, the last of these capacitors were manufactured in
2003 and should have disappeared from the market. However, the problem still
occasionally appears.
Bulging, leaking electrolytic capacitors
To increase consumer confidence, many manufacturers have started using solid
polymer capacitors.
Solid polymer capacitors
Chip Creep
Chip creep was a significant problem with early motherboards. Socket-mounted
chips tend to work out of their sockets as the motherboard expands and contracts
with temperature cycles. When a computer failed to boot or randomly locked up,
the first thing to do was push each chip back into its socket (accompanied by a
click as each chip reseated). Since most chips are now soldered in place, chip
creep is a rare problem.
