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How to Test PSU DC Output Voltages to Determine if Faulty
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 5volts 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.
These tests can be carried out with the Power Supply Fitted or removed from the computer.
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.
1. To Check The HDD 4-Pin Molex Power Connector Voltages:
The maximum voltage that will be measured will be no more than 12v/12.6v.
The Multi-meter should be set to DC 20 Volts as shown. The meter display will show 00.0 (i.e. - 0 Volts). NOTE: Any number after the decimal point can be ignored
The computer is best laid on its side when taking meter readings for ease of access.
Next open the case and power up the computer:
Care should be taken here as the fans will be spinning, certain components will be hot to the touch and observe ESD precautions.
The Anti-static wristband should be worn and attached to the case or an Earthing Point. (If you do not have one, simply earth yourself on the metal part of the computer case periodically)
Locate the HDD 4-pin Molex.
The Red Probe should be inserted into the right-hand side of the connector (Yellow Wire) The Black Probe should be inserted into one of the two centre holes (Both of which are negative)(Black Wires).
The reading should read 12.4V
NOTE: You can also take a reading between the connector and the computer case, the voltage reading will be the same (12.4V), as shown.
A reading should also be taken between the RED wire on the back of the HDD Molex and the computer case, this will show a reading of around 5V.
NOTE: This method can be repeated for testing the voltages for Red and Yellow wires on the CD/DVD Drive Molex Connector and for testing Molex Fan Connectors and CPU Connectors, some examples below.
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.
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.
*****ALWAYS RECHECK YOUR WORK WHEN WORKING WITH POWER SUPPLIES*****
Computer type PC/Desktop System Manufacturer/Model Number Home Built OS Windows 7 Professional x64 SP1 CPU Core i7 3770K Motherboard Gigabyte GA-Z77P-D3 Memory Crucial Ballistix Sport 8GB Graphics Card ASUS GeForce GTX 650 Ti Sound Card On board Monitor(s) Displays ASUS 22 W/S Screen Resolution 1920 x 1080
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Computer type Laptop System Manufacturer/Model Number HP Pavilion dm1 Notebook PC OS Windows 7 Home Premium x86 Service Pack 1 - Linux Mint Mate 14 x64 CPU AMD E-450 APU (64-Bit) @ 1.65GHz Dual-Core Motherboard HP 3387 36.0A (Socket FT1) Memory 4GB DDR3 @ 676MHz Graphics Card AMD Radeon HD 6320 Graphics Sound Card Beats Audio - IDT High Definition Audio CODEC Monitor(s) Displays LCD HP Monitor Screen Resolution 1366 x 768 @ 60Hz
Keyboard Standard PS/2 Keyboard Mouse Synaptics TouchPad V 7.5/Logitech USB Wireless PSU Microsoft Composite Battery - ACPI Case HP Cooling HP Cool Sense Hard Drives 500GB - SATA Hitachi HTS547550A9E384 Internet Speed 52.0 Mbps Antivirus Microsoft Security Essentials Browser Opera 15; Firefox 25.1; IE 11 Other Info NIC - Broadcom 4313GN 802.11b/g/n Wi-Fi Adapter
Belkin Black Laptop Cooling Stand
Computer type PC/Desktop System Manufacturer/Model Number Self Assembled OS Windows 7 Home Premium 64 Bit SP 1 CPU Intel Core i3 2120 @ 3.30GHz Motherboard Gigabyte Technology Co., Ltd. H61M-DS2 DVI Memory Corsair 2GB x2 (Single-Channel DDR3 @ 665MHz) Graphics Card 2047MB GeForce GTS 450 (ZOTAC International) Sound Card Onboard (Realtek High Definition Audio) Monitor(s) Displays LG Flatron E2040T Screen Resolution 1600x900
Keyboard Logitech MK220 Mouse Logitech MK220 PSU uMAX 750 watt. Case iBall Cooling Air/ Fans Hard Drives Western Digital 1 TB
Seagate 500 GB Internet Speed BSNL Broadband Antivirus Microsoft Security Essentials Browser Waterfox Other Info Dell Studio 15" Laptop
Computer type PC/Desktop OS Windows 7 Professional 64bit CPU AMD Athlon (tm) X2 5200+ Dual Core 2712 Mhz Motherboard Asus Memory 4GB Graphics Card Nividia GeForce 8600 GTS- DIED 25/7/2013 R.I.P Sound Card None Monitor(s) Displays 22" Yuraku LCD (Dont ask) Screen Resolution 1280x960
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Computer type PC/Desktop System Manufacturer/Model Number Custom Built OS Windows 7 Professional x64 Sp1 CPU AMD FX 8 core 8350 Black edition 4.2GHZ Motherboard SABERTOOTH 990FX/GEN3 R2.0 Memory 16GB Ram DDR3 Graphics Card Asus HD 7870 2GB GDDR5 GHZ edition (HD7870-DC2-2GD5-V2) Sound Card Motherboard Built in Monitor(s) Displays Dell LCD SP2008WFP 22'' Monitor Screen Resolution 1440 x 900
Keyboard Wired Dell keyboard Mouse Wireless Logitech mouse PSU Rosewill Stallion Series RD700 700W ATX12V V2.3 SLI Ready Case Rosewill ARMOR-EVO Gaming E-ATX Mid Tower Computer Case Cooling 220mm, two 120mm, and four 60mm fans,CORSAIR Hydro H55 Hard Drives 1TB Western Digital Black Edition 7200 RPM (Main Drive)
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