Question about HP Pavilion A635W PC Desktop

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I hadn't turned my hp Pavilion a635w desktop off for some time but, I decided to turn it off before I left for Colorado. I was gone for a week. When I got home I tried to turn the PC on and it wouldn't. Finding out my power supply was no good. So I replaced it and when I powered the PC up it showed a screen that I believe was the BIOS screen. It showed specs in the computer. All the info was in a off white color but, in bright white there was a message that read no system clock DDR3 I think. So I was told to replace the battery on the motherboard witch I did. After I did that the PC powers up but, the monitor won't display anything. I tried unplugging the monitor for 30 seconds and still no display. So I tried the monitor on another PC I have and the monitor worked fine. So I know it's not the monitor with the problem. The problem lies in the PC. So with what I've tried to explain. I was hoping you can help pin point the problem with my PC.

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  • HP Master
  • 5,660 Answers

1) There is a such thing as a bad Power Supply. New or not.

2) You may not have all required power cables plugged in.

Besides the ATX main power cable, there is also a 4-pin ATX +12 Volt power cable, that has to be plugged into the motherboard.

This cable,

http://www.playtool.com/pages/psuconnectors/connectors.html#atx12v4

This is HP Support, and the Motherboard Specifications page,

http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00069442&tmp_task=prodinfoCategory&lc=en&dlc=en&cc=us&site=null&lang=en&key=null&product=425875

I would like you to scroll down to the illustration of the motherboard.
To the left of VIA KM400A is a small square. To the top of the small square is printed ATX12V
This is where the 4-pin ATX +12 Volt power cable plugs into.

(The motherboard chipset is the Northbridge chip, and the Southbridge chip.
The VIA KM400A chip is the Northbridge chip. Should be under an aluminum finned Heatsink)

I would also like you to clear CMOS Error codes.
Computer unplugged from power press the Power On button, and hold it in.

Hold it in for a count of 5 seconds. (And I mean at least 5)
Let go of the Power On button.
Do this procedure 2 more times.

This action will clear CMOS Error codes, and reset BIOS back to the factory default settings.
Plug the computer back into power. WAIT 1 minute, then turn the computer on.

Be sure ALL power cables are plugged in, and plugged in tightly.

A) ATX main power cable. (20-pin ATX main power cable)

B) 4-pin ATX +12 Volt power cable

C) All 4-pin standard Peripheral power cables.
1 is for the Harddrive.
1 is for the CD or DVD optical drive, ( Or 2 if more than 1 optical drive)
1 may be used in conjunction with an adapter cable, and used for power to a computer case fan.

3) Make sure the ram memory module/s are seated in tightly. (Module = 'Stick')

You may wish to clean the gold plated contact pins on each ram memory module.
The gold plated contact pins develop corrosion.

Computer unplugged, and you have followed Anti-Static Precautions, remove each ram memory module.
Use a pencil eraser to clean each contact 'strip'.
If you use an eraser on the end of a pencil, refrain from letting the metal band contact the contact pins.
Just takes a few strokes of the eraser on each contact pin.

After you have finished cleaning a contact strip it may look as though you have done nothing at all
I assure you that you have. Doesn't take much corrosion to make a bad contact.
Use air to remove the eraser dust before you reinstall the ram memory.
If air from a can of compressed air for computers is not available, air pressure from your mouth is sufficient.

If this doesn't solve the problem please post back in a Comment.
We will go on to test the various voltages coming out of the Power Supply.

(If a multimeter is not available an economical unit can be purchased. Most auto parts stores carry them, as well as a multitude of other stores. A $5 to $20 unit will do just fine.

The voltages involved are 3.3 Volts, 5 Volts, and 12 Volts.
ALL are DC voltage.

Two D cell flashlight batteries produce 3 Volts DC )

Regards,
joecoolvette

Posted on May 29, 2011

  • 2 more comments 
  • joecoolvette
    joecoolvette May 30, 2011

    Thank you for the rating most kind!

  • Josh Heilman Jun 02, 2011

    I have tried your suggestions and I'm still not receiving power to the VGA connection. I also tried putting a new memory module and no luck.

    Thanks Again,
    Josh

  • joecoolvette
    joecoolvette Jun 03, 2011

    Thank you for updating your progress. (Or lack of at the minute. It's okay, read on)

    Some questions I need to ask;

    Power

    1) I need to know that all of the required power cables from the PSU (Power Supply Unit) are connected up, and connected tightly.

    A) The 20-pin ATX main power cable.
    Down in tight until the lock snaps over the tab. (Female connector on motherboard has the tab)

    B) The 4-pin ATX +12 Volt power cable.
    Same as above.

    C) The 4-pin standard Peripheral power cable, (Molex), plugged into the back of the 80GB IDE (PATA) harddrive.

    D) The 4-pin standard Peripheral power cable to your optical drive. (It's an IDE unit also. CD/DVD drive)

    Answer is yes to All of the above?
    I need to know that the PSU is a good unit. Not a bad unit with a weak voltage power rail.
    If you do not have a multimeter an economical unit cab be purchased for around $5 to $10.

    There are three voltages I would like you to check coming from the new PSU.
    1) The 3.3 Volt power rail
    2) The 5 Volt power rail.
    3) The 12 Volt power rail.

    ALL Orange wires coming from the PSU are 3.3 Volts. (All DC voltage)
    ALL Red wires are 5 Volts.
    ALL Yellow wires are 12 Volts.
    ALL Black wires are Ground wires.

    (Again, two D cell flashlight batteries produce 3.3 Volts. { DC } This is the voltage you will be dealing with. Very low. High voltage { AC} comes into the PSU, but is lowered down to the above stated low DC voltages. These low voltages are what the computer uses)

    Multimeter's vary.
    Basics;
    The Red probe lead is the Positive lead.
    The Black probe lead is the Negative lead.
    Set the multimeter's Function knob to DC voltage.
    If there is a scale range also set it to the 0 - 50 Volts scale.

    The Positive (Red) lead goes to the power wire. Orange, Red, or Yellow.
    The Negative (Black) lead goes to ANY Black wire you see. ALL are Ground wires.

    Computer plugged into power, power button pressed on;
    Place the Positive probe lead down into the back of any connector with a Red wire. (5 Volts)
    For an example let's use a 4-pin standard Peripheral power cable,

    http://www.playtool.com/pages/psuconnect...

    The photo to the far right shows the back of the connector. The probe lead goes down into the back of the connector, into the socket hole with the Red wire.
    RIGHT NEXT TO THE WIRE.

    The probe lead must go down into the socket hole pretty far. (3/8th's Inch?)
    The probe lead must touch a metal terminal.
    (At the end of every wire in a connector is a metal terminal. The probe lead must touch that metal terminal)

    Place the Negative probe lead into the socket hole with a Black wire.
    Scale read 5 Volts or very close to it?

    Do the same for the Yellow wire. (12 Volts)
    (11 to 13? OK. Less than 11? No good)

    PSU checks out?

    At this point I need you to run a visual test.
    Need to know if there are obvious signs of damage to the motherboard.
    With your being gone, and assuming the computer was left plugged into power, and the Ethernet cable still attached, I need you to check to see if an electrical spike may have caused damage.

    Computer unplugged from power, computer case open, flashlight in hand;
    Check the Electrolytic Capacitors on the motherboard. They may, or may not show obvious signs of damage.

    Info;

    http://www.capacitorlab.com/visible-fail...

    Post back we'll go on form there.
    Regards joecoolvette












  • joecoolvette
    joecoolvette Jun 03, 2011

    Edit: "We'll go on FROM there." (I'm going to have to fire my proofreader. Wait a minute! That's me! lol!)

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  • Expert
  • 106 Answers

More than likely you have accidentally unseated your video card open the box and press the video card tightly into the pci slot.

don't forget to give testimonial and the votes 4 thumbs up if I helped.

Posted on May 29, 2011

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