Electronics
amps	Measures a current's strength or rate of flow.
ohms	Measures a conductor's resistance to electricity.
volts	Measures the electrical pressure in a circuit.
watts	Measures the elecrical power in a circuit.
continuity	Indicates the existence of a complete circuit.
resistor	Slows down the flow of current in a circuit.
capacitor	Holds electrical current.
diode	Allows electrical current to flow in only one direction.
transistor	A semiconductor that stores one binary value.

     The primary measurements of electricity are volts and amps. Voltage measures pressure, and amps measure current. Current isn't needed for voltage. When a water faucet is turned off, it still has water pressure.

     Ammeters, ohmmeters, and voltmeters measure specific properties of electricity, a multimeter or DVM combines all the above tools into one tool.

AC and DC Current

     AC or alternating current changes directions about 60 times per second, that is, it switches polarities. In DC or direct current, the flow of electricity is in one direction only. In DC power, negatively charged particles seek out positively charged particles, creating a direct electrical current flow. This means that if you were shocked by holding a negative 12 Volt battery terminal with your left hand while holding the positive terminal in your right hand, current would travel from your left arm to the right arm.

Basic Elecronics

     A digital circuit is an electronic circuit that accepts and processes binary data using the rules of Boolean Algebra - the logic AND, OR, XOR, NOT, etc. A conductor, such as copper, carries an electrical current. An insulator, such as rubber, doesn't carry an electrical current. A semiconductor is a material that toggles its state from conductor to insulator when electrical current is applied. A semiconductor is simply an on / off switch. The switch is turned on and off with electrical spikes. Transistors, resistors, capacitors, and diodes produce logic gates. Logic Gates create circuits, and circuits make up elecronic systems.

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The Power Supply

     The power supply converts AC into DC in 5 different voltages: +5V, -5V, +12V, -12V, +3.3V. The PC can experience a number of problems from external power sources:

• Line noise - small variations in the voltage of the power line.
  
• Power surges - A power spike or overvoltage in the power supply.
  
• Brownouts - undervoltage in the power supply.
  
• Blackouts - complete power failure.
  

Surge Suppressors

     The primary component of a surge suppressor is a Metal Oxide Varistor (MOV). A surge suppressor reduces power problems by absorbing spikes and surges and by smoothing out line noise (also known as line conditioning). Two main features of a surge suppressor: clamping voltage and clamping speed. Clamping voltage is the voltage at which the suppressor begins to protect the computer. Clamping speed is the time lapse before the protection begins, or how much time elapses between detection and protection. Not all surge suppressors include line conditioning.

• Energy Absorption: Surge suppressors are rated in Joules, which measure their capability to absorb energy. The higher the rating, the better the protection: 200 Joules is basic protection, 400 is good protection, and 600 is superior protection.
  
  
• Line Conditioning: The line conditioning capability of surge suppressor is measured in decibels. The more decibels of noise reduction, the better the line conditioning.
  
  
• Levels of Protection: Surge suppressors have three levels of protection that indicate the maximum number of watts the suppressor allows to pass through to anything plugged into it. The standard ratings are 330 (best), 400 (better), and 500 (good).
  
  

Power Supply

The primary power supply components are:

• Power cord: Plugs into the AC power outlet.
  
  
• Passthrough connectors: Located on the back of the power supply. In the past, these connectors were used primarily to plug a monitor into the power supply, which enables you to turn the monitor on and off with the computer's power switch.
  
  
• Power switch: On older PCs, this switch extended through the case wall from the power supply on a back corner of the PC. On modern PCs, the switch is electronic.
  
  
• 110V/220V Selector switch: Allows you to select between the two voltages.
  
  

The power supply provides the following voltages to the motherboard and drives:

• +5V - The standard voltage of motherboards for all 8086, 286, 386, 486 processors below 100MHz, and peripheral boards.
  
  
• +12V - Used primarily for disk drive motors and similar devices. Modern motherboards pass this voltage to ISA bus expansion slots.
  
  
• -5V and -12V - Included in most power supplies for compatibility with older systems. Most modern motherboards don't use either of these voltages.
  
  
• +3.3V - A 486 100MHz or above, and all Pentium chips run at 3.3V.
  
  

     The power supply's motherboard connectors on a Baby AT board are called a P8 and P9. They are two 6 wire connectors. They are installed on the Baby AT motherboard correctly when all four of the black wire, or grounds, are together in the middle. The ATX form factor uses a 20 wire keyed connector which is easy to identify its orientation.

     If no form factor is mentioned, assume it to be the AT or Baby AT form factor. You should not unplug an AT power supply when working on an AT computer because it provides a positive ground. With the ATX form factor, the board is always hot, even when the power switch is off, you should unplug an ATX motherboard when servicing it.

     Here are a few symptoms that indicate a power supply problem: The power light on the front panel is off, the power supply fan isn't operating, the computer sounds a continuous beep or doesn't beep at all, the computer sounds a repeating short beep, the computer displays either a POST error in the 020-029 series (power good signal error) or a parity error.