On the case of the computer power supply, it is indicated which voltages must be present at each of the outputs. Often, however, these voltages do not correspond to the nominal ones. To check if this is so, they need to be measured.
Instructions
Step 1
With a working computer, you can measure the output voltages of the power supply using the analog-to-digital converters built into the motherboard. Reboot the machine and immediately start pressing the "Delete" or "F2" key (depending on the board model) repeatedly until you enter the CMOS Setup utility. Select "PC Health Status" from the menu and you will see what voltages are actually present at the outputs of the power supply.
Step 2
Many motherboards do not show the standby power supply voltage in CMOS Setup. Measure it with a multimeter operating in the DC voltage measurement mode at the 20 volt limit, connecting it between the black and purple wires. Make sure that it is not too high compared to the nominal value in both operating and standby modes of the computer.
Step 3
If the computer is inoperative, there is no "PC Health Status" function in CMOS Setup, or if you doubt the correct operation of the ADC on the motherboard, use a multimeter operating in the same mode and at the same limit to measure all voltages. Carry out the measurements with the machine running, taking care not to cause a short circuit with the probes.
Step 4
Use a special stand to test the voltages of the power supply under varying load. Load each of the outputs with parallel-connected automotive lamps in such a quantity that the total current consumption is slightly less than the nominal current for this output. Note that at voltages of 5 and 3.3 V, car lamps consume a reduced current: measure in advance what it is at these voltages on one lamp. By turning off some of the lamps at each of the outputs, you can simulate a decrease in the load on the power supply. Carry out the measurement in the same way as in other cases.
Step 5
If this or that voltage is too high, immediately stop using the power supply and send it in for repair. Most likely, the voltages increased due to the drying out of electrolytic capacitors, but only a qualified master can independently change them even in a switched off high-voltage device, such as a switching power supply.
