TAKE OUT BATTERY, REMOVE MAINS SUPPLY, HOLD POWER BUTTON DOWN FOR 30SECS PUT POWER SUPPLY IN ONLY DO NOT PUT IN BATTERY TURN ON LAPTOP NOWPUT IN BATTERY
AC power adapter
How the AC adapter worksThe most common type of AC power adapter involves a small box, withone wire to go to the computer and another wire to go to the wall.There is usually an LED light on it, to tell you that it is on. (Is itlit on yours?) By the way, Apple notebook power adapters often have anLED that is actually built into the side of the computer, not into theadapter box, so obviously it won't light up when it's not connected tothe computer.
The power adapter box does several things. It lowers the voltage from the wall's 120 volts AC to typically 19 volts DC (it will be labeled with the exact voltage). It includes some power noise filtering. It often includes an automatic circuit breaker
or overload detection. If this gets tripped, you can generallyreset it if you unplug it from everything for a few minutes.
You can measure the voltages on your AC adapter with a multimeter. When it is unplugged from the computer but still plugged in to the wall,it is normal to find that the voltage may be 1 to 3 volts higher than theprinted output rating.
Troubleshooting: AC Power adapter LED is off when you plug the adapter into the wall but not into the computerHas it been overloaded? Is the power strip turned on / is the outlet working? Is the cord from the adapter to the wall fully plugged in on both ends (try wiggling)?Your adapter may be fried- try borrowing an indentical adapter from a friendand seeing if that one will work in it's place (but do not plug it in to your computer, or you might fry your friend's adapter).
Troubleshooting: Check output voltages with a volt meter/multimeterFor those of you with circular connectors, your task is easy. Measure the voltage between the inside and theoutside. A diagram on the adapter's label will tell you which should be positive and negative
For those of you with the 3-pin Dell power connectors, I don't have a diagram for you yet, sorry.If you try measuring each of the three possible pairs of pins, you should get 20 volts between oneof the pairs.
Power distribution inside the laptop
How laptop power distribution works
Okay, the power comes into the plug on the back of the computer. This connects it to metal tracesinside the mainboard of the computer. These will be connected to voltage regulators
which often output 5 volts, 12 volts, 3.3 volts, and the CPU voltage; they sometimes look like the image at right.
These will be connected to cylindrical capacitors distributed throughout the mainboard. Capacitorsact like tiny, fast batteries, supplying extra power where needed to maintain a steady voltage during high demand.
Finally, power goes to all the devices that need it.
Power for the LCD display
is usually done seperately. Generally, LCD backlights require high voltage to operate.A component that might be called a power inverter will step the voltage upto what is needed for the backlight. Sometimes this inverter is a discrete andreplacable component, and sometimes just a chip on your mainboard. It is also involved in the brightness control.
is an important part. It supplys power to theinput-side of the voltage regulators, just like the power from the AC adapter.Additionally, there is a charging circuit, which uses the power from theAC adapter prior to the voltage regulators, to charge the battery. (By the way, this is why the AC adapter voltage is always rated higher than the battery's rated volatge-- you need higher voltage for charging.)
There is a separate page exclusively for Laptop Battery Problems
Short circuitsAnywhere in your laptop, physical or electrical damage can cause a short circuit.A short circuit will consume all available power, causing your laptop to not turn on.If your power adapter LED comes on when you plug it into the wall, but then goes offwhen you plug in the laptop, you probably have a short circuit.
Troubleshooting short circuitsAn ohm-meter / multimeter will read less than ~3 ohms when you measure theresistance between sides of power going into a short circuit. When measureing betweenthen power pins going into the back of your computer, consider the 2 pins whereyou expect voltage to be applied by the AC adapter. If the resistance indicatesa short circuit, this is bad.
A common trick to help isolate possible problems is to try to removing anything that mightbe a short circuit. Take out the battery, the hard drive, the DVD/CD drive, the floppy drive, PCMCIA cards, USB devices,miniPCI cards. See if the computer will then turn on.
You might have luck with a thermal imager (see story below) to find a hot spot caused by theshort circuit.
Spilled liquidLaptops exposed to small amounts of spilled liquid are repairable in some cases. Liquid can cause the following types of damage:
- Short circuit due to wet liquid (problem goes away after liquid evaporates)
- Short circuit due to dried liquid residue
- Corrosion (especially bad with soda such as Coke or Pepsi)
- Electronic components damanged by above short circuits
Immediately when a spill occurs, you typically want to turn off thelaptop, turn the laptop upside down (so the liquid goes out the sameway it came in), remove the power and battery, and allow to dry atleast overnight.
To remove dried liquid residue: Try removing the keyboard andcleaning any components that have dried liquid, by using distilledwater and Q-tips.
Computer turns off randomlyYour computer can turn off due to: power overload in the AC adapter,overheated processor / clogged fan,overheated battery, pushing the power button, Windows telling it to,the BIOS telling it to, loose wires (especially the power cord), orintermittent short circuits.
The most common problem is cooling. Try going somewhere air conditioned. Notice if the fan isbroken or clogged with dust (common older HP problem).