1. Power Supply
Lesson 15
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2. 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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3. Connections to Peripherals
Molex – large connector (HDD, CD-ROM)
Berg – small connector (FDD)
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4. 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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5. 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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6. 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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7. connection to Motherboard
AT Power Supply
connection to Motherboard
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9. 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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10. connection to Motherboard
AT Power Supply
connection to Motherboard
AT – 12 wires; 2 plugs
ATX – 20 wires; 1 plug
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11. 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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12. 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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14. Other Cooling Products
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