How to Test PSU DC Output Voltages to Determine if Faulty
Information
The Internal ATX Power Supply converts the Alternating Current (AC) from the mains input to a Direct Current (DC) output that is required for the computer to work.The typical voltages supplied are 3.3 volts, 5.0 volts, -5.0 volts, 12.0 volts, -12.0 volts.
The 3,3 and 5 volts are typically used by the digital circuits, whereas the 12-volt is used to power the motors found in Disk Drives and Hard Drives. It is also used to Power the CPU. The following tests involve testing the voltages across the HDD, Motherboard, CPU, CD/DVD ROM Drive Power Connectors.
Warning
NEVER ATTEMPT MAINTENANCE ON POWER SUPPLIES AS THEY CAN BE DANGEROUS
EVEN WHEN THE POWER REMOVED. If a fault is suspected with the PSU then the first step is to take VOLTAGE readings, then substitute the POWER SUPPLY with a good quality brand, with the same MAINS VOLTAGE and WATTAGE.
PSU and PSU Connectors Overview.
Here's How:
1. To Check The HDD 4-Pin Molex Power Connector Voltages:
2. To Check The Motherboard 24-Pin Power Connector Voltages:
Next we can check the voltages across the 24-Pin Motherboard connector, simply connect the
RED probe to each colour in turn, whilst the Black Probe is touching the computer case, the readings will be similar to those shown.
NOTE: The BLACK and WHITE wires are not classed as COLOURS and are rated 0V,
you need not test between the case and these connections.
You can of course test between these and any COLOUR in order to get a reading.
If we look at the relationship between the COLOURS and the VOLTAGE, we will see
that ALL the COLOURS carry exactly the same voltage, as shown.
This is very useful to note, because if a Device has failed then you can check that it is operating at the correct voltage if you measure the same colour Wire on a different Device.
Note
A few notes to consider when replacing or buying a new PSU:
Most entry level systems are usually supplied with a basic generic, unbranded PSU. If you are building a medium to high spec system, it is highly recommended that you use a branded PSU such as Antec, OCZ, Corsair etc.
Many engineers state that 10-15% of the system budget should be used on a quality PSU.
When replacing Power Supplies Always check the Voltage is set to the correct setting on the rear of the PSU, either 110v/115v or 220v/230v. Setting the Power Supply voltage switch to the incorrect Input Voltage could seriously damage the Power Supply and possibly cause damage to other components of your computer.
The correct voltage is determined by the country where the Power Supply is located.
(I.E.- UK 220v/230v USA 110v/115v.
Final Word!!
*****ALWAYS RECHECK YOUR WORK WHEN WORKING WITH POWER SUPPLIES*****
Cheers Dave :)
Credit and thanks to Brink, Arc and Essenbe for their support.