Will Corsair HX750i PSU power ASUS A8V Deluxe motherboard?

[Crimsom_247]

The ASUS A8V Deluxe motherboard has a 20 pin ATXPWR socket with all 20 pins present. My old PSU expired and a new Corsair HX750i PSU was purchased. I note that pin 18 of the HX750i ATXPWR 20 pin plug is not included because modern PSUs do not include -5Vdc power output.

ASUS have ceased to support their A8V Deluxe motherboard, but volunteered from a technical point of view that HX750i should work because the missing pin 18 was used in the past to provide -5Vdc power to motherboards in order to power the former Industry Standard Architecture (ISA) expansion slots. Any PSU designed since about 2005 won't even be producing -5Vdc power so it has nothing to connect to, so pin 18 is missing altogether. My ASUS A8V motherboard has one AGP and five PCI expansion slots and does not have ISA expansion slots. So my ASUS A8V motherboard does not require a PSU with -5Vdc power output (or does it).

Having installed the new Corsair HX750i PSU, the system does not boot. The motherboard's green led illuminates, but the on/off power button led does not illuminate and none of the fans power on. I have checked all the connections and they seem to be correctly seated. Most perplexing because everything was working fine before the old PSU expired.

So I am wondering if the ASUS A8V motherboard requires the -5Vdc power supply. Has anyone else provided a modern PSU replacement for their old ASUS A8V motherboard and got it to boot? Kind regards.

 

[ko888]

The Corsair HX750i has a (20+4)-pin ATX motherboard connector. Just detach the (+4)-pin portion and plug the 20-pin portion into the motherboard connector.

The -5V rail was used for really old school floppy controllers and some ISA bus cards. The motherboard itself does not use -5V. It was only old ISA bus add-in cards that used that rail.

 

[Crimsom_247]

Hello ko888, having installed the new Corsair HX750i PSU, the system does not boot. I am now trying to understand why the system does not boot so that I can apply the remedy. The motherboard's green led illuminates, but the on/off power button led does not illuminate and none of the fans power on. I have checked all the connections and they seem to be correctly seated. Most perplexing because everything was working fine before the old PSU expired. How do I find out what has changed, so I can fix it! Kind regards.

 

[ko888]

Is the 4-pin CPU power connector plugged in?

The green SB_PWR LED on the motherboard indicates whether or not the motherboard is receiving standby power from the PSU's +5Vsb rail. The +5Vsb rail is actually a separate power supply on the PSU's circuit board. The +5Vsb remains powered when the PSU is receiving AC power and the PSU's AC power switch is turned on. It's independent of whether the rest of the system is powered on or not. It powers the motherboard circuitry that controls the Power On signal that gets sent to the PSU.

If the motherboard detects that there is a power problem (e.g. out of spec voltage on any rail) then it won't tell the PSU to turn itself on (i.e. PS_ON# or Power On is a signal sent from the motherboard to the power supply).

... but the on/off power button led does not illuminate and none of the fans power on. ...

The power button LED should be connected to the PLED pins on the motherboard's front panel header. It should only light up when the main PSU circuit (i.e. +12V, +3.3V, +5V rails) turns on sending power to the motherboard and peripherals like cooling fans.

Make sure your computer case's power switch leads are connected to the PWRSW pins on the motherboard's front panel header.

There may be an incompatibility between the PSU and the motherboard.

I have owned an ASUS A8V Deluxe, many years ago, but have never used it with a current PSU.

 

[Crimsom_247]

Hello ko888, thank you for your detailed response.

I will respond to your questions in the same order.
(1) Is the 4-pin CPU power connector plugged in? Yes.
(2a) Is there is a power problem? The ATX ASUS A8V Deluxe motherboard requires the ATX 12V PSU to provide a minimum of 8A +12Vdc and 1A +5Vsb and have a minimum PSU total power output wattage of 350W. The system may become unstable or may not boot up if the power is inadequate. The Corsair HX750i PSU output is 62.5A +12Vdc and 3A +5Vsb and has a PSU total power output wattage of 750W. So the new Corsair ATX 750W PSU seems to be more than adequate to power the old ATX ASUS A8V Deluxe motherboard.
(2b) Motherboard's Power On signal: There is no ATX ASUS A8V Deluxe motherboard stipulation of ATX 12V PSU having or not having a -5Vdc power supply. The motherboard has an ATXPWR pin 18 but I am unsighted if this is connected to anything.
(3) Is the PWRSW cable seated? Having pushed cables around to install the new Corsair ATX 750W PSU, I have checked the PWRSW cable seating at both ends and they seem to be correctly seated.
(4) Is the power button LED connected to the PLED pins on the motherboard's front panel header? Yes.
(5) Is there an incompatibility between the PSU and the motherboard? I am unable to answer this question. Corsair and ASUS Technical Help Desk declined to comment. OuterVision Power Supply Calculator recommended CORSAIR CX-M series CX750M 750W 80 PLUS BRONZE, and I purchased the higher spec CORSAIR HXi Series HX750i 750W 80 PLUS PLATINUM which has all Japanese 105°C capacitors for high performance PCs where long life reliability is essential.

The inability of the system to boot is most perplexing. Everything was working fine before the old PSU expired. How do I find out what has changed, so I can fix it! Kind regards.

 

[ko888]

Have you performed the following power supply test just to confirm that the main part of the PSU is functioning?

Corsair Video FAQ: How to test a Corsair power supply

[flash=640,390]https://www.youtube.com/v/5FWXgQSokF4[/flash]

 

[Crimsom_247]

Hello ko888, thank you for providing the video. I have not performed the power test described.

Rather annoyingly the Corsair HXi connectors and their wiring are all black in colour. Corsair did not include a leaflet giving guidance on which connector is used for a particular purpose. Using a paperclip to give a false motherboard signal to enable PSU power is problematic. The HXi series is so efficient that the fan does not spin at low loads. (I have used the fan self-test feature with the HXi only connected to AC power source and the HXi fan spins when the button is depressed.) Using the power test described in the video with little or no load will not spin the HXi fan. The video does not include how to connect the external fan, so I need help.

The HXi series includes the 'Corsair Link' feature which is used to monitor power supply performance. So I downloaded and installed the Corsair Link Dashboard application onto my laptop so that HXi power supply performance can be remotely monitored. But the HXi package contents failed to include the 'Corsair Link' USB cable. I have raised a Corsair ticket but they have not agreed to supply the missing 'Corsair Link' USB cable.

So I have ordered and I am waiting for a Power Supply Tester to arrive.

I am struggling to find out what has changed, so I can fix it! Kind regards.

 

[ko888]

On power supplies that don't use color coded wiring you have to go by pin position. Note what side of the connector has the latch on it.

 

[Crimsom_247]

Hello ko888, thank you for providing the picture with the paperclip connected to pin 14 PS_ON (green) and pin 15 GND (black).

(1) The Corsair video does not include how to connect the external fan to one of the other unspecified connectors. The HXi series is so efficient that the HXi fan does not spin at low loads. Using the power test described in the video with little or no load will not spin the HXi fan. So connecting an external fan to power on or some other diagnostic indicator is required for this Corsair diagnostic test to give me an indication that the HXi PSU is functioning.

(2) Getting the digital/analogue output from the Corsair Link (C-Link) connection on the rear of the HXi would be the ideal diagnostic. Corsair has provided this feature to monitor power supply performance. However the Corsair Link USB cable is missing from the HXi package contents.

(3) My third option is to purchase a Power Supply Tester. Kind regards.

 

[ko888]

Do you have a cooling fan to test with? If yes, what type of connector does it use (see the following image)? If it's the same as the one shown on the right then you can just connect it directly to one of the modular cables that has a 4-pin Molex peripheral connector on it. If it is like the left or middle connector shown in the image then you'll need to use an adapter like the one shown in the second image.

 

[Crimsom_247]

Hello ko888, thank you for keeping in touch and for providing the images. I note the "How to test a Corsair power supply" video shows a cooling fan with four pin Molex plug. However, my 12Vdc ultra quiet cooling fan in the midi tower case has the three pin plug shown on the left of the first image. My three pin plug has three wires (black, red, white) and not the two wires (black, red) shown in the first image. I do not have and would have to purchase the adaptor shown in the second image. (I do not have a cooling fan with a Molex plug as shown in the Corsair video and would have to purchase it.) So I have purchased a Power Supply Tester and I am awaiting its arrival.

I continue to postulate that connecting my laptop to the digital output signal from the Corsair Link (C-Link) USB COMM PORT on the rear of the HXi power supply may be the ideal remote diagnostic. Corsair has provided analogue and digital C-Link ports to monitor power supply performance. The USB 2.0 Mini B to USB 2.0 A cable is not included in the HXi package contents. I have downloaded the Corsair Link Dashboard software onto my laptop and the CorsairLink4 dashboard illustration appears to be fully replicated. I did not find the CorsairLink4 dashboard feature to display the HXi PSU digital/analogue output via the laptop's USB port. Perhaps it needs the 'missing' USB cable to be plugged in for this remote diagnostic to become available. I hope that the PSU information has more detail than that shown in the CorsairLink4 dashboard illustration. Kind regards.

 

[Crimsom_247]

Hello ko888, thank you for keeping in touch. The Power Supply Tester has been delivered and connected to the Corsair HX750i power supply unit (PSU). The diagnostic output on the LED display reports -12V = -11.9V, +12V2 = +12.0V, +5Vsb (stand by) = +4.9V, PG (Power Good) = 280ms, +5V = 4.9V, +12V1 = 12.0V, +3.3V = +3.2V and I note that the -12V, +5Vsb, +5V and +3.3V outputs are low.

The Power Supply Tester does not have a user manual. So I do not know what PG = 280ms means or if the dc voltage outputs are what they should be. Does the four low dc voltages indicate that the Corsair HX750i PSU is defective?
Kind regards.

PS: The 'Corsair Link' feature is connected to my laptop and also reports the HX750i power in = 15W, power out = 6W and calculated efficiency = 40%. HX750i Temperature = 20 degrees C and Fan speed = zero rpm.

 

[ko888]

Hello ko888, thank you for keeping in touch. The Power Supply Tester has been delivered and connected to the Corsair HX750i power supply unit (PSU). The diagnostic output on the LED display reports -12V = -11.9V, +12V2 = +12.0V, +5Vsb (stand by) = +4.9V, PG (Power Good) = 280ms, +5V = 4.9V, +12V1 = 12.0V, +3.3V = +3.2V and I note that the -12V, +5Vsb, +5V and +3.3V outputs are low.

The Power Supply Tester does not have a user manual. So I do not know what PG = 280ms means or if the dc voltage outputs are what they should be. Does the four low dc voltages indicate that the Corsair HX750i PSU is defective?
Kind regards.

PS: The 'Corsair Link' feature is connected to my laptop and also reports the HX750i power in = 15W, power out = 6W and calculated efficiency = 40%. HX750i Temperature = 20 degrees C and Fan speed = zero rpm.

All of your voltages are within the ATX12V Power Supply Design Guide Specifications. Your time to PG (Power Good) is also well within spec (i.e. recommended that it be less than 460ms).

 

[Crimsom_247]

Hello ko888, thank you for your very informative email complete with confirmation that the output of the Corsair HX750i power supply unit (PSU) is within specification.

As reported earlier, I am struggling to find out why the ASUS A8V Deluxe motherboard system does not boot. This modern HX750i PSU does not have a -5V output, so does this mean that the ASUS motherboard does not provide the signal telling the PSU to work? What would happen if the paper clip induced signal was permanently included in the 20 pin ATXPWR plug when connected to the ASUS motherboard?

Is it possible to use the -12V output to provide the -5V output to pin 18 of the 20 pin ATXPWR plug and thereby satisfy the previously unknown ASUS motherboard requirement to see -5V and provide the signal to switch on the PSU? For example 12V to 5V DC-DC Step Down Power Module.

Is there a permanent solution to reinstate computer system boot? Kind regards.

 

[ko888]

I have no idea if the A8V Deluxe is looking at the -5V rail's voltage. If it is, then that would explain why it won't tell the PSU to turn on.

Whether or not that "HiLetgo 12V To 5V DC-DC Step Down Power Module" will work can only be determined by testing. I have no idea if that module's boot state time to correct output voltage is quick enough to register properly with the motherboard.

 

[Crimsom_247]

Hello ko888, thank you for your candid response. I am looking for a permanent solution to reinstate computer system boot. What, if any, are the consequences of permanently connecting the PowerSupply_ON (PS_ON Green) wire to the Ground (GND Black) wire? When connecting the 20 pin ATXPWR plug to the motherboard socket, is it prudent NOT to have the motherboard's Ground pin and PowerSupply_ON pin connected (i.e. the PS_ON wire in the plug is moved)? Kind regards.

 

[ko888]

Hello ko888, thank you for your candid response. I am looking for a permanent solution to reinstate computer system boot. What, if any, are the consequences of permanently connecting the PowerSupply_ON (PS_ON Green) wire to the Ground (GND Black) wire? When connecting the 20 pin ATXPWR plug to the motherboard socket, is it prudent NOT to have the motherboard's Ground pin and PowerSupply_ON pin connected (i.e. the PS_ON wire in the plug is moved)? Kind regards.

You could try to wire up a toggle switch between the PowerSupply_ON (PS_ON Green) and Ground (GND Black).

 

[Crimsom_247]

Hello ko888, thank you for your recommendation to insert a toggle switch between the PowerSupply_ON (PS_ON Green) and Ground (GND Black). Should the toggle switch be placed between the power supply unit (PSU) and the 20 pin ATXPWR plug (i.e. isolated from the pin 18 on the motherboard's socket)? I am puzzled why a toggle switch is advocated in preference to a bridging wire. Is the PowerSupply_ON signal from the motherboard continuous or only at power on?

Are there any other checks that should be undertaken? Is it OK to connect the 20 pin ATXPWR to the power supply tester and connect the 4 pin 12V plug to the motherboard? From the earlier dialogue, is there any merit in testing the motherboard's 12V integrity by seeing if the case and CPU fans rotate?

I am looking for a permanent solution to reinstate computer system boot and do not want to damage the new PSU or the existing motherboard. Your help and understanding appreciated. Kind regards.

 

[ko888]

Using a bridging wire forces the PSU to always be on when the PSU's AC power switch is turned on.

Using a jump start toggle switch in place of the bridging wire allows you to emulate, to a degree, what the motherboard should be doing. After initiating a power off in the Operating System you can then turn off the toggle switch and that should turn off the main output rails of the PSU.

I wouldn't modify the power supply's connector. I would recommend using an extension cable and modify it to add the jump start toggle switch.
https://www.amazon.com/StarTech-8-Inch-Power-Extension-ATX24POWEXT/dp/B000FL60AI

 

[Crimsom_247]

Hello ko888, thank you for your insight. Am I missing something in the technical reasoning? Not sure if a toggle switch inside the case is required when the PSU mains switch at the rear of the PSU can seemingly perform the same operation and power down the computer system.

Is there merit in testing the motherboard's 12V integrity by seeing if the case and CPU fans rotate? Is it OK to connect the 20 pin ATXPWR to the power supply tester and connect the 4 pin 12V plug to the motherboard?

Are there any other checks that should be undertaken? Kind regards.

 

[ko888]

Using an externally accessible jump start toggle switch saves wear and tear on the PSU's AC power switch. Ultimately it's your decision as to what you want to implement.

Didn't you already test the PSU's 20-pin portion of the main ATX (20+4)-pin connector? The ATX (20+4)-pin connector has a connection to the +12V rail that would have been checked by your tester. The 4-pin CPU power cable is connected to that same +12V rail in the PSU.

 

[Crimsom_247]

Hello ko888, thank you for keeping in touch. My ideal is to determine if the manual PowerSupply_ON (PS_ON Green) signal works. If not, then this is not a solution. Hopefully the modern PSU will tolerate a fault condition rather than be destroyed. Similarly I hope that the motherboard will survive the manual imposition of connecting its signal pin permanently to its neutral pin. Please let me know that I have understood your recommendation.

Yes, the power supply tester confirmed the 12V output of the PSU. However, I have no way of testing the motherboard's function, other than to plug the PSU into the motherboard's socket. The PSU and motherboard/CPU/memory are expensive items and I wish to avoid destroying either or both. Kind regards.

 

[ko888]

Your Corsair HX750i has the following protection circuits:
• Over Voltage Protection
• Under Voltage Protection
• Over Power Protection
• Over Current Protection
• Over Temperature Protection
• Short Circuit Protection

It is suppose to be designed to prevent destruction of any attached devices if the PSU should fail.

Since your A8V Deluxe isn't sending the PS_ON# signal to the PSU you don't have much of an option other than bridging the green wire to ground to emulate what a functioning motherboard would do.

You can also try to find/buy an old PSU with the missing -5V rail hoping that it will solve your problem.

Ultimately the best solution is to upgrade the CPU, motherboard and memory to something using more recent technology.