Question about HP Compaq Presario Media Center SR1750NX (EL445AA) PC Desktop

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My computer will not turn on and the green light on the power supply is flashing.

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The Green light flashing on the Power Supply is a diagnostic LED light.
Flashing indicates a bad Power Supply.
Replace the Power Supply.

BEFORE you start:
1) Buy a can of compressed air for computers.
If the computer is dirty inside, and the Power Supply, use the can of air to clean.
Attach the plastic straw to the can of air's nozzle, break off the lock tab on the top of the nozzle.

Computer on a table, computer unplugged from power, computer case open.
Observe Anti-Static Precautions.

Anti-Static Precautions:
Your body carries Static electricity.
Static WILL fry out (Short Circuit) the hardware components inside a computer.

Power unplugged to the computer, TOUCH the metal frame of the open computer case.
This action will relieve your body of Static.
Should you leave your computer in the middle of working on it, upon your return be SURE to Touch the metal frame again.

Start at the top of the inside of the computer with the can of air, and go across from one side to the other.
Drop down a row, and spray air again.
(Squeeze the trigger in all the way when you start, let go when you reach the other side.
Just like a spray painter would)

Keep dropping down, and going across in rows, until you reach the bottom of the computer case.
In cleaning you'll run across the Processor Fan, and Heatsink.
This is a typical Fan/Heatsink combo, to illustrate. (Yours may look different),

The object under the Fan is the Heatsink.

[Typical construction of a Heatsink is a plate of metal with tall, thin fins protruding from it.
The plate of metal absorbs heat from whatever object it is placed against. {In this case the Processor. It is placed against the top of the Processor's case, with thermal paste in-between}
The tall, thin fins absorb heat from the plate, and radiate the heat away.
If a fan is used in conjunction with a Heatsink, as in this case, the air flow from the fan helps to dissipate the heat away from the fins]

Pay special attention to cleaning the fins of the Heatsink. They must be as clear as possible, and unrestricted from foreign material.
The Fan's blades, center hub, and surrounding cage, (Shroud), must be clean also. You may find that using Q-tips to break the surface of the 'Gunk' may help. Then the can of air can remove it. ('Gunk'. Dirt, dust, etc)

When using the can of air on the Fan, Do Not spin the fan too fast. Use short bursts of air.
(Press the trigger in all the way, let go quickly)
Spinning the fan faster than it was designed for may lead to premature failure of the fan's bearings.

To open the computer case, and remove the Power Supply:

Working on a table, remove all cables to the computer tower. If you are not sure where they go, (Pay particular attention to the speaker cables), this is the time to make notes, and possibly a drawing.
Open the computer case.

Facing the Front of the computer the Left side panel removes.
Facing the back of the computer there is a Thumb screw to remove.
It's in the middle on the edge. (Facing the back of the computer it's on the Right side)
The Thumbscrew does not remove all the way. Loosen it.
Use the formed handle in the side panel to pull the side panel back, then lift it off.
Lay the computer on it's side on a towel on the table. Open side up.

I'm looking at a Compaq Presario SR1517CL right now, from out of my shop.
Uses the same computer case design as the Presario SR1750NX.
I found no direct links to give you on HP Support for the SR1750NX except for the Specifications.
I would like you to download the PDF file - Upgrading and Servicing Guide for the SR1517CL.
This way you'll have a guide with illustrations for the following,

On the back of the computer are 4 Philips head screws to remove, which hold the Power Supply to the computer case.
On the back of the computer, and at the top of the computer case.
(Where the small fan is, and you plug in the power cord)
One on the Top Left, one on the Top Right, one on the Bottom Right, and the last one on the bottom left.

Once these screws are removed the Power Supply is free.
There are several power cables to remove now.

1) The 20-pin ATX main power cable:

The middle photo, and the photo to the right, show you the plastic Lock on the side of the connector.
It is hinged in the middle, and works on the same principle as a see-saw on a playground.
The photo to the left shows you the female connector on the motherboard, that this power cable plugs into.
Note the Lock Tab on the side.

The Top of the Lock on the power cable is squeezed in. This action brings it's hooked end away from the Lock Tab. Holding the Connector, wiggle it gently as you pull it up, and out. Do Not pull on the wires!

2) The 4-pin ATX +12 Volt power cable:

Removing is the same principle as the 20-pin ATX main power cable.

3) Standard 4-pin Peripheral power cable:

Power to the optical drive/s, and perhaps a computer case fan.
Note the rounded corners used for aligning when plugging in.

4) The SATA power cable:

Power for the SATA harddrive. Note that there are two connectors going to the harddrive.
The SATA power cable coming from the power supply is the longer one. Only plugs in, in one direction.
(The smaller connector is for the Data cable)

The Power Supply is just an ATX model. One used in over 80 percent of desktop computers out there.
(The ATX form factor for a Power Supply refers to it's power supply case shape, and size.
Approximately 6 inches Wide, 5-1/2 inches Long, and 3-1/2 inches Tall)

It is probably a generic unit made by Bestec, HiPro, Delta, or Maxpower.
300 Watt.
(You can use a larger Wattage power supply. Won't hurt the computer. A computer ONLY uses the power it needs, and No more)

Posted on Oct 12, 2010


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I just went through a heap of troubleshooting with power supply issues before swapping psu's and finding this was the solution to my problem. Had a closer look at my psu that was faulty, the green light was flashing on the psu, unplugged all components and thought that I now had a non-flashing green light on my psu, on closer inspection the light was actually flashing very fast so appeared to be an almost solid light...the psu was stuffed so replaced it and no more issues. If your power supply has a green light check to see if it is flashing when plugged into voltage with nothing connected to it. If it is a solid light then it is probably ok.

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If that doesn't do it then it has to be the motherboard at that point.

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Flashing Green Light on Power BESTEC Power Supply

This is an easy fix so here you go nice and simple:

Problem: Your motherboard circuit has been cut.

Causes: Power disconnected during operation. Power outage or short in the surge protector.

Symptoms: Flashing green light on both motherboard and power supply. System will not power on.


Step 1: Ensure that both the power supply and the motherboard lights are flashing green, not solid or off.
Step 2: While the power is on, disconnect the power supply from the motherboard. This connection is the largest of the connections and should be listed as the 'P1' or 'Primary' power connection.

Step 3: Wait until the green light on the motherboard stops flashing and check to ensure that the green light on the power supply is now solid. If it is not solid, disconnect the power to the power supply and wait until the light turns off completely. Then reconnect, it should be solid now.

Step 4: While the power is on, reconnect the P1 connection to the motherboard and you should now see that the light on the motherboard is solid.

Step 5: Power on your PC. The problem should not persist.

Warnings: If the power supply light remains flashing after you have restored power to it while it is disconnected from the motherboard, it may be a system failure in the power supply itself requiring replacement. Always be careful when working with an active or live power machine.

I hope this helped! Good luck!

Jun 23, 2008 | Bestec (ATX-250-12E) 250-Watt Power Supply

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