How to Use A multimeter to detect PC power supply faults

 

When you solve a user's PC fault, do not forget to use a multimeter to test the power supply. Learn some simple and easy-to-use skills to help you eliminate the possibility of power failure.

It may not seem obvious, but more than 1/4 of PC problems are related to power problems to some extent. You may think that if there is a problem with the power supply, the PC will not start up at all, and the culprit will be easily identified. But the problem is not always that simple. Power issues can also lead to deadlocks, abnormal restart, and intermittent startup problems. To ensure that you have learned all the basics, I will explain how to test the PC power supply with 10 thousand Gb/s on your power connection and motherboard.

Preparations

Because there are many brands of multimeter available, I cannot provide you with instructions on how to use a specific brand multimeter. So before you start, make sure you have thoroughly understood how to use your multimeter. Improper use may lead to a strong electric shock, or may damage your multimeter.

Power Supply Knowledge

The purpose of a power supply is to convert a 220 v ac to a DC power available for the PC. Generally, the power supply converts an AC to 12 V, 5 V, or 3.3 v dc. 12 volt DC is used to drive a device with a motor, such as a hard drive and a CD-ROM drive. 5 V and 3.3 V output are used to supply different components on the system motherboard.

Almost all currently used PC power supplies are at or ATX architecture power supplies. The main difference between the two is the number of connectors connecting wires. However, if you do not consider the type of power you are using, all power supplies have basic components. The first is the power connector, which connects the power to the socket. Next is the motherboard power supply, which is transmitted through a set of cables extended from the power supply. The power supply also has a fan (you can easily find and solve the problem by checking whether the fan rotates properly ).

Test power connector

To start the diagnosis process, make sure that the PC has been powered off and power off. Next, check the voltage selector on the back of the PC near the fan to make sure it is at 220 volts. You can see an example in Figure 1.

Upload

Download Attachment
(10.88 KB)

Figure 1: Make sure the power supply is set to 220 volts.

The next step is to check whether the fan is rotated. If the fan is rotating, the main power input must be working. If the fan is not rotated, either the fan is broken or the master power connector does not receive any current. Check whether the connection is disconnected, adjust your multimeter to a voltage level higher than 220 volts, and then test the power outlet, as shown in figure 2.

Upload

Download Attachment
(22.56 KB)

Figure 2: Be careful! The best way to avoid electric shock is to first place the multimeter on an unplugged wiring board, and then insert the wiring board into the wall power outlet.

If the outlet produces proper power, use your multimeter to perform a connectivity test on the power cord, as shown in 3. If the outlet is powered on and your power cord passes the connectivity test, the fan is broken and the power supply must be replaced.

Upload

Download Attachment
(23.97 KB)

Figure 3: perform a connectivity test on the power cord.

Test motherboard Power Supply

Depending on whether your motherboard is at or ATX, you need one or two connectors that connect the power supply to the motherboard. No matter which type you are, you should remove the computer from the outlet before testing the motherboard power supply.

If you use an AT power supply, you have two connectors, P8 and P9, which connect the power supply to the system motherboard. Separate P8 and P9 from the system motherboard. Although both connectors are locked to prevent misplacement, occasionally reversing these two connectors is still possible. Reversing these connectors will almost certainly damage the motherboard and possibly damage the power supply. When switching the P8 and P9 connectors on the motherboard, remember that the two Black Ground Wires should be adjacent to each other.

ATX motherboard power connector, 4, uses a separate P1 connector, instead of P8 and P9 connectors. This connector is locked to prevent being inserted from the back.

Upload

Download Attachment
(12.38 KB)

Figure 4: The ATX motherboard connector uses a separate P1 connector.

Both at and ATX power supplies provide 12 volts, 5 volts, and 3.3 volts to the system motherboard. The reason for different voltage levels is that different system motherboard components require different sizes of current.

Note that because of a built-in logic circuit, the fan in the ATX power supply will not rotate unless the power supply is connected to the system motherboard. Therefore, the ATX power supply must be connected to the system motherboard before running. However, at power does not need such a connection.

In Figure 4, you can see that the P1 connector of ATX is usually a set of wires connected to a 20-pin connector. In Figure E, you can see an illustration of the meaning of each pin.

Upload

Download Attachment
(21.13 KB)

Figure 5: P1 connector layout.

The first step is to understand the role of each pin, but the appearance of an wiring bar on the P1 connector will make this much easier than you think. The pin is located between 15 and 16. By setting the wiring bar in these pins, You can intuitively understand what other pins represent.

Use A multimeter on an ATX power supply. As long as the PC is plugged in, pin 9 should have 5 VDC (volt DC ). This is the same whether the main power switch is on or off. Because it is usually a purple wire, you can easily identify pin 9. Using A multimeter to detect a 5 volt DC on Pin 9 is a good way to start testing to identify whether the system motherboard is connected to any power source.

After you test pin 9, test the voltage of various 12-VDC circuits. You may have noticed several black and several ** wires on the P1 connector. ** The 12-VDC circuit is labeled by a wire. to test these circuits, adjust your multimeter to the 15-vdc or 20-vdc range (depending on the multimeter type you are using ). Next, power on the PC, put the red probe on a ** wire of the P1 connector, and then put the black probe on a black wire. Because the PC has been powered on, the P1 connector must be connected to the system motherboard. Therefore, you must use the probe as shown in Figure F.

Upload

Download Attachment
(18.4 KB)

Figure 6: connect a ** wire with a red probe and a black wire with a black probe.

After the probe connection, your multimeter should display a voltage between 11 and 13vdc. If the power supply ages and causes some problems I described above, the voltage would be below this standard. If the voltage you see is between 10.5 and 11vdc, your PC needs a new power supply. If the voltage you see is less than 10.5vdc, your PC can be restarted only when the power supply is changed. You should also pay attention to the 5-vdc and 3.3-VDC circuit voltage drops. However, because you start with a relatively small power supply, these voltage drops less. Therefore, we recommend that you test the 12-VDC circuit.

Conclusion

Problematic power supply is not the easiest way to detect PC components. During Fault Detection and troubleshooting, most IT professionals prefer to first detect more common PC hardware problems, therefore, power supply is often ignored. However, if 10 thousand Gb/s exists, you can quickly detect the correct current of all connections. Most of the main problems with power supply are power input and motherboard, so by detecting these aspects as I mentioned above, you should be able to eliminate the possibility of power supply problems.