Which of the following statements is not true regarding laptop power supplies

The BIOS (also called System Setup) is a firmware that is embedded onto the system board (motherboard) of the computer. Updating the BIOS to the latest version helps the computer recognize the AC adapter correctly.

WARNING: Dell laptops must have their battery that is installed and connected to the AC adapter before you begin to update the BIOS. Some Dell laptops must have at least a 10% battery charge before you begin the BIOS update.

To update the BIOS to the latest version, see the Dell knowledge base article Dell BIOS Updates.

If the AC adapter type is not recognized by the laptop, see the Dell knowledge base article Forcing a BIOS Update without the AC adapter that is attached on a Dell Laptop. Before trying to force the BIOS update, read the disclaimer below.

CAUTION: If the battery charge is less than 10%, you may be able to force the BIOS to update from within the DOS environment. A failure during this process will cause permanent damage to the system board of the computer. Users must proceed at their own risk. Dell shall not be liable for any loss, including but not limited to loss of data, loss of profit, or loss of revenue, which customers may incur by following any procedure or advice set out in this article.

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Dell Inspiron, XPS, OptiPlex, Precision and Vostro desktop systems include a power supply with a built in self-test (BIST) feature that helps diagnose the health of the power supply unit. The LED indicator on the PSU helps identify if the power issue is caused by the power supply unit.

No Cause Associated.

The PSU BIST is found on the back panel of the desktop computer, next to the power cable connector (on some smaller chassis types, you may need to remove the system cover to see the BIST on the side of the PSU).

PSU BIST with a test button
PSU BIST without a test button

How to use the BIST to diagnose power supply issues?

How to run self-test using the button on the PSU

1. Turn off the system.
2. Press the BIST button on the system and check whether the LED lights up.
3. The light should be solid on not flickering or flashing and the power supply fan should also turn on to speed. If the fan is not spinning up properly this should be considered a BIST failure even if the LED lights up.

• If the BIST LED lights up, then the power supply can deliver power to the system but something else is impeding the POST process. The next step is to check whether the power button might be at fault. If it is not, you should go to the following article for No POST troubleshooting.
• If the BIST LED does not light up or the PSU fan does not spin correctly, then the power supply can not deliver power to the system and could be caused by any component connected to the power supply or the power supply itself. The next step would be to isolate the source of the power failure by disconnecting parts from the PSU, you should go to the following article for No Power troubleshooting.

How to run self-test without the button on the PSU

1. Turn off the system.
2. Disconnect the power cord from the PSU, and wait for 15 seconds.
3. After 15 seconds, connect the power cord back to the PSU.
4. The LED light should stay on for 3 seconds and then turn off.

• If the BIST LED lights up, then the power supply can deliver power to the system but something else is impeding the POST process. The next step is to check whether the power button might be at fault. If it's not you should go to the following article for No POST troubleshooting.
• If the BIST LED does not light up, then the power supply can't deliver power to the system and could be caused by any component connected to the power supply or the power supply itself. The next step would be to isolate the source of the power failure by disconnecting parts from the PSU, you should go to the following article for No Power troubleshooting.

Desktops & All-in-Ones, Fixed Workstations

Last Published Date

20 Sep 2021

Version

6

Article Type

Solution

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This chapter is from the book 

The power from a wall outlet is high-voltage AC. The type of power computers need is low-voltage DC. All computer parts (the electronic chips on the motherboard and adapters, the electronics on the drives, and the motors in the hard drive and optical drive) need DC power to operate. Power supplies in general come in two types: linear and switching. Computers use switching power supplies. The main functions of a power supply include the following:

• Convert AC to DC
• Provide DC voltage to the motherboard, adapters, and peripheral devices
• Provide cooling and facilitate air flow through the case

One purpose of a power supply is to convert AC to DC so the computer has proper power to run its components. An ATX power supply does not connect to the front panel switch as the old AT-style power supplies did. With the ATX power supply, a connection from the front panel switch to the motherboard simply provides a 5-volt signal that allows the motherboard to tell the power supply to turn on. This 5-volt signal allows ATX power supplies to support ACPI, which is covered later in the chapter, and also lets the motherboard and operating system control the power supply. Figures 4.24 and 4.25 show the front panel connections to the motherboard on two different computers.

Figure 4.24. Front panel connections to a motherboard

Figure 4.25. Another view of front panel connections

Another purpose of a power supply is to distribute proper DC voltage to each component. Several cables with connectors come out of the power supply. With ATX motherboards, there is only a 20- or 24-pin connector used to connect power to the motherboard. The power connector inserts only one way into the motherboard connector. Figure 4.26 shows an ATX connector being inserted into a motherboard.

Figure 4.26. Installing an ATX power connector on a motherboard

Another purpose for a power supply is to provide cooling for the computer. The power supply’s fan circulates air throughout the computer. Most computer cases have air vents on one side, on both sides, or in the rear of the computer. The ATX-style power supply blows air inside the case instead of out the back. This is known as reverse flow cooling. The air blows over the processor and memory to keep them cool. This type of power supply keeps the inside of the computer cleaner than older styles.

Electronic components generate a great deal of heat but are designed to withstand fairly high temperatures. Auxiliary fans can be purchased to help cool the internal components of a computer. Some cases have an extra mount and cutout for an auxiliary fan. Some auxiliary fans mount in adapter slots or drive bays.