Unable to turn PC on with hdd connected

[KarolisG]

Hi, I have HP Compaq dc7900 Convertible Minitower. And I have strange problem.

When I plug the computer into an electrical outlet, it blow electrical fuses at home.

BUT if I unplug the hard drives (power cord), and then plug the computer into an electrical outlet, everything works.

So, the only way to turn on this computer is to do this:
1. unplug the hard drives;
2. plug the computer into an electrical outlet (than the motherboard receives the power and the green LED lights up);
3. reconnect the hard drives power cords
4. then turn on the computer with the power button.

After this computer works fine. But if I turn off the computer AND unplug it from the electrical outlet, I have to repeat this sequence again (if the motherboard loses power). Otherwise the electrical fuses blow at home.

I've already tried:
I changed the CPU (to the same E8500)
I changed the power supply to another one

I think the hard drives themselves are not the cause of the problem as they are three, one is brand new, two are older, all from different manufacturers. I tried to disconnect only some hard drives, I tried different combinations.

It’s some electrical overload or something like this, but I don’t understand what can cause it. Thanks for any help.

[banhien]

@KarolisG 

>>>> 1. unplug the hard drives;

Is it an external HDD ?

>>>>> When I plug the computer into an electrical outlet, it blow electrical fuses at home

Definitely your HDD causes this problem and it is much better remove it for good, otherwise it may blow your house too.

Regards.

[KarolisG]

Thank you for replay!

These are internal hard drives. Not external.
As i mentioned, i use a total of three internal hard drives:

1 x SEAGATE Barracuda 7200 2TB 7200rpm 3.5''

2 x Western Digital WD5002ABYS 500GB 7200rpm 3,5" 

The problem occurs regardless of how many and which of these hard drives are connected.

SEAGATE Barracuda is a new one and i used it for a month on another computer (AMD based) without any problems.

So I doubt if hard drives are to blame for this. On the other computer they are running without any problems.

They also work on this computer when I turn compiuter on in the above mentioned sequence...

[VH2000]

It is not an overload. It's an electrical short circuit.

[KarolisG]

Yes you are right. I understand that. but what can lead to it?

The computer's power supply works (I have two, both tried). No short circuit until a hard drive is connected to it. And even connecting a hard drive doesn’t always cause a short circuit, but only when the computer is plugged in with hard drives already connected. If the computer is plugged into an electrical outlet and the hard drives are connected after that (before pushing power button), then there is no short circuit and the computer and hard drives operates completely normally.

Thus, a short circuit is created by the power supply only when it has to power the hard disk at the same time as it receives power.

Because I have two power supplies of the same model (hp original parts), either it’s a power supply design problem, or both power supplys are faulty in the same way.

I don't understand how a hard drive (its presence connected) can cause a short circuit in the power supply's 220 v input. After all, a hard drive gets a maximum of 12 volts. Even if the hard disk is shorted (which I doubt), the power supply should not shorten the 220v current received from the electrical outlet. After all, they are separated by a electrical transformer. I have no doubt that the power supplies were designed with the possibility of experiencing a short circuit on the computer side. Or am I wrong?

[VH2000]

There are some issues with ATX-Powersupplies when you don't use the original. For that cases there are some adapters on the market. 

[KarolisG]

Sorry, mistyped (edited previous post)... I use hp original PSU part HP 460968-001 PC6015 365W 

[VH2000]

The spin-up current of a HDD can go up to 2,5 [A] ! 

So try this: Start the computer and switch it off.

Unplug, wait for 2-3 seconds and plug in again. 

[KarolisG · Accepted solution]

Thank you, I tryed your offer. If I plug on the power after 2-3 seconds, everything works, nothing bad happens. however, i think this is because the motherboard has not yet lost its electrical charge (led still lit). but if I wait about 5-6 seconds (until the motherboard led goes out), then the result is the same - knocked out the fuses in home.

BUT I think the problem is the motherboard after all. I disconnected the power supply from the motherboard. At 24 pin connector I connected the green wire to ground (this forces the power supply to turn on). And I connected four hard drives to the power supply. And everything works. I can turn the power off and on no matter how many times. Hard drives spins. No knocking out of fuses.

Therefore, I assume that the short circuit is caused by the motherboard...

[VH2000]

So you found the solution! Good to hear. But I don't think that it is a reason to exchange the mainboard.