Power Supply
Lesson 15
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Power Supply
Converts 110 volts AC to DC
Supplies voltages:
+5 – memory, processor, drive logic, video, and
keyboard controller.
+ 5 and +12 – peripherals.
- 5 and -12 – sent to expansion slots only.
Pentium requires +3.3
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Connections to Peripherals
Molex – large connector
(HDD, CD-ROM)
Berg – small connector
(FDD)
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Connections to Peripherals
Computer will only start when power good
signal is sent (+5 volts) - takes 250
milliseconds.
Power supply will not function unless there is
a load placed on it.
Power supply cools the PC and itself. The fan
requires +12 volts and moves air in the case.
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Form Factor
Power supply, motherboard and case must
be the same.
PC/XT - original style - obsolete
AT Desktop - obsolete - 286
AT Tower Type (mini tower, mid tower and full tower).
Baby AT Type
All ATs used two separate 6-pin plugs. P8 and P9 plug
into P1 and P2 on the motherboard.
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Form Factor
Black on Black Rule:
Two black wires
together, the
motherboard will be
happy.
Separate the blacks
and your computer
will smoke!
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AT Power Supply
connection to Motherboard
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ATX Power Supply
ATX - current style used with Pentium
Power supply is on all the time it is plugged in, this supplies 5V
standby power to the computer
Positive pressure ventilation - blows air from outside and across
motherboard. (The original specification for the ATX, however,
manufacturers have reverted back to the old style, negative
pressure systems of the AT class supply)
IDIOT PROOF- All the connectors are keyed and will only
connect to the motherboard and peripherals one way. It is
impossible to connect them incorrectly
WTX – used with Pentium IV motherboards, and has an
extra 12 Volt connector to supply power to the CPU.
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AT Power Supply
connection to Motherboard
AT – 12 wires; 2 plugs
ATX – 20 wires; 1 plug
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Troubleshooting
The Power Supply
You may have a defective power supply if:
System fails to start or locks up on startup.
Spontaneous rebooting of the computer or
intermittent lockups during normal operation.
Intermittent parity check memory errors.
Hard disk and cooling fan fails to stop due to loss of
12 volts.
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You may need a new
power supply if:
Your system is completely dead: no power, no
fans, no drives.
Smoke comes from the rear of the computer.
Circuit breakers or fuses blowing.
The computer freezes and a cold start solves
the problem.
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Other Cooling Products
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