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Your computer’s power supply unit (PSU) provides all necessary power throughout your system. For the purpose of simplification throughout this text, we will recognize your computer Power Supply Unit as a PSU. Because this task requires you to work with high voltage, we will include a few electrical safety tips as we progress. There are specific tools needed for this task and we will discuss them in the tools portion of our instructions.

 

 

Tools

1.      The first tool we will need is a multimeter. We will be measuring voltages, both Alternating Current (AC) and Direct Current (DC).

2.      You will need an electrical screwdriver set, so you will have a variety of screwdriver heads available if needed.

3.      A grounding strap to prevent being subject to Electrostatic Discharge (ESD) which is the transfer of a static electrical charge from one item to another.

4.      A safe and static-free work environment will benefit both you and your system.

 

Step 1:

Shut Down Computer System
1. Press ON/OFF button located on front panel above the gateway logo.
2. Once button is pressed, the blue light on bottom will turn off. Check that all front panel lights on your system go out.
3. Listen to make sure system fans and other components are shut down.
Ensuring that all lights and components shut down is one of the most important safety habits we will present.

4. Make sure you are looking at the rear of your unit. Remove the main power plug located on the upper left hand side of the unit next to fan. This is a 3-prong plug. Removing this plug further ensures there is no power going into the unit, and prevents possible damage to you or the unit.
5. Gently lay computer on its left side as you’re facing the rear.
6. At this time we will be removing the top panel. To begin, remove the 2 thumb screws located one on the right and one on the left of the top panel, by turning counterclockwise.
7. Slide top panel toward you until it frees itself from front panel, and then left to remove completely.
8. Place panel in safe area near your work area.
9. Now your computer system’s working components are visible to you.
10. Continuing with our focus on safety, let’s ensure that our system motherboard power indicator light is off. This is located in front of your P1 24-inch plug from your PSU to the motherboard. (See figure B1).
11. If light is on, check to see if your 3-prong plug is disconnected before moving on.

Step 2:

 

 

Removal of Power Supply Unit

1.      Assuming there is no power present; let’s begin disconnecting the PSU from the system unit.

2.      First, locate and get familiar with the power supply unit.

3.      The PSU is a large, silver metal box on the upper left hand corner of your system. It has a wiring harness and multiple plugs attached.

4.      Again, it is very important for safety that everything connected to the PSU is disconnected.

5.      There is one 4-pin Molex plug attached to your main hard drive. It is located on the top front left in your drive bay. Firmly grip the 4-pin Molex on both sides and wiggle and move back toward you. Do not remove plug by pulling on wires because it’s unsafe and may damage system.

6.      Remove the next 4-pin Molex from your CD unit. Continue to practice the same safety with plug removal as you continue this process.

7.      Detach the mini Molex attached to your floppy drive.

8.      We will disconnect the PSU from your motherboard now.

9.      Let’s begin with our main power cable to the motherboard. This is the 24-pin Molex on your motherboard.

10.  This 24-pin Molex plug has a release tab on its front. Grab plug with one or both hands; press on the tab and wiggle aggressively while pulling upward until plug is removed.

11.  The remaining plug is called the P4 because it has 2 yellow and 2 black wires. It provides power to your processor, and also has a release tab on its front. Once again, grab firmly with one hand, press tab on front, wiggle while pulling upward until plug is removed.

Step 3:

Removal of Power Supply Unit
1. Assuming there is no power present; let’s begin disconnecting the PSU from the system unit.
2. First, locate and get familiar with the power supply unit.
3. The PSU is a large, silver metal box on the upper left hand corner of your system. It has a wiring harness and multiple plugs attached.
4. Again, it is very important for safety that everything connected to the PSU is disconnected.
5. There is one 4-pin Molex plug attached to your main hard drive. It is located on the top front left in your drive bay. Firmly grip the 4-pin Molex on both sides and wiggle and move back toward you. Do not remove plug by pulling on wires because it’s unsafe and may damage system.
6. Remove the next 4-pin Molex from your CD unit. Continue to practice the same safety with plug removal as you continue this process.
7. Detach the mini Molex attached to your floppy drive.
8. We will disconnect the PSU from your motherboard now.
9. Let’s begin with our main power cable to the motherboard. This is the 24-pin Molex on your motherboard.
10. This 24-pin Molex plug has a release tab on its front. Grab plug with one or both hands; press on the tab and wiggle aggressively while pulling upward until plug is removed.
11. The remaining plug is called the P4 because it has 2 yellow and 2 black wires. It provides power to your processor, and also has a release tab on its front. Once again, grab firmly with one hand, press tab on front, wiggle while pulling upward until plug is removed.

Step 4:

Equipment Preparation
Now we will use the multimeter, but before using it we want to make sure it is functioning properly.
• If your meter has an ON/OFF switch on bottom, make sure it’s on.
• Your meter should have two cables: one black, one red.
• To see if the meter is working:
o Place your black cable in the common slot on your meter for Ohms testing.
o Set dial on front of meter to read 200k Ohms
o If meter is working properly, it will read the number (1) when the probes are held apart from each other; and the number (00.0) when the probes are touching.
o If you don’t get the same results, check to see if your cables are in the right slots and that your dial is on the right setting.
• Insert black cable in the black port that says (COM) on your meter.
• Insert red cable in whichever port has the voltage source you’re testing—either AC or DC. In this case we’re going to be testing DC, so we’ll use that port.
o Anytime you are testing for AC/DC voltage or Ohm’s, you should set your meter for a value equal to or greater than what you are testing. For example, if you’re testing for 115 volts, set your meter to 200 volts.
o The maximum voltage we will be using for this test is +12 volts DC.




Testing
1. Now we begin testing for the operating power required to run your system. Most of your voltage is between -20 volts DC and +20 volts DC, so set your meter to -20 volts DC.
2. We will be testing your P1, 24-pin plug (see figure B1). Make sure it is firmly in place and that the latch tab is in the correct position.
3. We are testing for several voltages, each represented by a designated color wire as follows: RED= (+5v DC); WHITE= (+12v DC); BLUE= (-12v DC); ORANGE= (+3v DC). Be sure to test all wires to ensure all voltages are present on your plug.
4. When measuring, be sure to allow a 10% tolerance + or – in your reading. See “Acceptable Ranges” column in figure (B1).
5. Place your black probe in the ground wire hole on your P1. (These are the black ports marked COM).. Be sure to insert probe and press firmly until it makes contact with the metal casing inside the hole.
6. Once your ground is firmly in place, use your red probe to test each of the voltages. See “Your Readings” column in figure (B1) for my results.
7. If all readings are within the acceptable ranges, and you’ve made sure all connectors are firmly in place, now it is time to turn your system on, and check for start-up indicators. Remember to practice electrical safety when restarting your system.

Voltage Acceptable Ranges Your Reading Wire Color Within Range?
Y or N
-5 -4.5 to –5.5  
+5 +4.5 to +5.5 +5.16 Red Y
-12 -10.8 to –13.2 -11.90 Blue Y
+12 +10.8 to +13.2 +11.90 White Y
+3.3 +3.0 - +3.63 +3.38 Orange Y
Figure B2

Step 5:

Final Steps
1. Press ON/OFF button on front of system. Listen for the fan starting. Make sure your 5-volt DC green indicator light on the motherboard illuminates, and that all front panel component lights are on. If all components are functioning properly, you can begin reassembling your computer.
2. Turn ON/OFF button to OFF position. Replace your side panel—remember to tighten your two thumb screws finger tight. Place your system back in the upright position.
Nice Harbor Freight tool set.

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