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Unexpected behavior with AX750W. The power supply won’t discharge. Is this normal?


jeff151

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Other power supplies act in this manner:

Power down the system in the normal manner (software shutdown or via motherboard power switch). The power indicator LED on the motherboard is lit (expected).

Turn off the power switch on the power supply.

Press the power button on the motherboard.

The lights flash and fans pulse for a brief moment as the power supply discharges.

The power indicator LED on the motherboard goes off.

It’s now safe to mess with the hardware.

Or:

Sitting at the BIOS screen. Turn off the switch on the power supply. The system shuts off and the power indicator LED on the motherboard quickly shuts off indicating there is no power to the motherboard.

Every system I have worked on acts like this.

 

My new AX750 acts unlike any other power supply:

Same conditions/hardware.

Power down the system via software or the motherboard power switch. The power indicator LED on the motherboard is lit (expected).

Turn off the power switch on the power supply.

Press the motherboard power switch. Nothing happens. The fans don’t pulse and the power indicator on the motherboard stays lit.

The power indicator on the motherboard stays lit for 45 seconds. It then dims out.

Or:

Sitting at the BIOS screen. Turn off the switch on the power supply. The system shuts down but the power indicator LED on the motherboard stays lit for about 45 seconds. Pressing the motherboard power switch makes no difference.

 

Connecting the AX750 to a power supply tester shows that the +5VSB is the line that does not drop when the switch is turned off.

 

This is my first AX750. Is this odd behavior typical? It’s a pain to wait nearly a minute to feel like it’s safe to start messing with the hardware.

 

Other info: ASUS Z68 motherboard. The motherboard power cable set is hooked to the power supply via the correct connections as far as I can tell. Tried both sets of 4x4 motherboard cables. Two different brands of power supplies act in the expected manner with the same hardware.

 

Thanks for your help.

Jeff

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  • Corsair Employees
The time it takes to dissipate the charge built up in the capacitors will vary from MB to MB, so taking up to 1-2 Min to do this is not uncommon. It really depends on how efficient the components are that are on the MB and with advances in computer technology in general components have became more efficient and use less power so the time to totally dissipate may be a bit longer on newer MB's So from what you have posted I would not call it abnormal. Would need more information to make a determination.
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Thanks for the reply.

But that’s not what I asked.

I understand that all power supplies will dissipate the stored charge over time. The better/bigger supplies take longer.

 

What I’m questioning is why does this AX750 power supply not discharge after the power supply is disconnected from 120v and the power button on the motherboard is pressed.

 

All other power supplies on systems I have built or serviced will discharge the stored energy in the power supply after being disconnected from 120v and the power button on the mother board/case is pressed.

After the power button is pressed the discharge is indicated by a blink of LEDs, a fan pulse (if the power supply is big enough) and a nearly immediate dimming of the power indicator LED.

Some small cheap supplies will discharge themselves very quickly and may not have enough stored energy to pulse the LEDs and fans when the power button is pushed.

 

The AX750 I have will not do this.

After disconnecting the AX750 from 120v. Pressing the motherboard/case power button – nothing happens – discharge wise.

The stored charge dissipates as if the power button on the motherboard/case was not pushed. Again this takes about 45 seconds.

This is not the typical behavior of any other modern power supply I have used before.

 

Once again I only have this one example of an AX750 to go by. But other power supplies connected to the same hardware will discharge after being disconnected from 120v and the power button on the motherboard/case is pushed.

 

If I do not push the power button on the motherboard the other power supplies act just like the AX750. They take a long time to internally drain the stored energy.

 

Can any other users tell me it their AX750/AX850 discharge in the normal manner when disconnected from 120v and the power button jumpers/switch on the motherboard are connected?

This forum has lots of experienced uses and should be able to spot this difference easly.

If all the other AX750 power supplies act this way, then OK, it’s some sort of design difference. If this is by design I’d sure like to know why.

 

Thanks again,

Jeff

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  • 1 month later...

I know its a bit of a late reply but i don't get around these forums too often, so for what its worth to future forumusers i'll post a reply of my own in case.

 

I think RAM guy's reply makes sense honestly, it probably varies from motherboard to motherboard on how quickly it discharges completely.

I have an AX750 myself with an Asus Sabertooth P67 and flipping the switch, pushing the on/off button a couple of times it takes a few seconds for the led on the board to turn off completely.

45Seconds does seem like a long time to me personally however, i think on my system its around 10seconds tops.

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jeff151

It seems that it is a bit longer for your system than what I would call average but I am not sure this is a problem. Do you have any problems with the system at all or any type of Voltage problems when it is running? If the answer is no I would not worry it is likely fine. If you do then we can try and replace the PSU if you like. However, what you have posted so far does not suggest that is needed to me. So I will leave it up to you.

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