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I have a machine with:

  1. Mobo: ASUS P5QL PRO
  2. RAM: DDR2- 8GB
  3. GRAPHICS: Gigabyte R7 360 series
  4. HDD: 6 discrete units plugged in 6 SATA ports. (some are 1TB, some are 500GB, some are 320/250GB)

I power this machine with two PSU units, instead of one, both pulled from old Dell desktop machines. I used two PSU units to fulfill the power drawn by the system, for I can't spend enough on this old machine to put in a single 600W PSU.

First PSU 305W powers the motherboard and its peripherals except HDDs.

Second PSU 220W: powers the six HDDs through their SATA power connecters. A different PSU was used previously and worked OK.

Problem is with the second PSU. The usual way of connecting GREEN to GND usually turns on a CPU. But when I put the jumper in this unit, the PSU fan doesn't start and the PSU doesn't supply power.

Now for testing, I put this second Dell PSU 220W to power the motherboard. It works fine and system comes on as soon as I push power button.

I read somewhere that some PSUs wouldn't supply power just grounding Green wire till they sense some load on power rails. But in my case I am connecting all six HDDs to the secondary PSU while I do the trick. Still it does not switch on to power the HDDs.

So does it mean that all six HDDs' power load is not enough to switch ON this specific PSU?

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  • Where is the PSU from? Is it fully ATX compliant? If it's ATX compliant, shorting between the green and GND should start the PSU up. If it doesn't, it's either faulty or not ATX compatible.
    – Stese
    Nov 26, 2018 at 12:53
  • your troubleshooting skills need some work ..... why would you connect six HDDs to the PSU before you have determined that a single HDD works? ..... connect only one HDD ..... does it turn on now? ....... the PSU may need a load on the highest current output (probably the +5V rail)
    – jsotola
    Nov 27, 2018 at 6:25
  • jsotola, I said that I am powering my 6 HDD's with a secondary PSU. I am facing problem powering them with this Dell PSU. obviously for troubleshooting I would power them one by one when at least PSU is confirmed OK.
    – sunnyimran
    Nov 27, 2018 at 20:20
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    @K7AAY I confirmed power rails are compatible on their recommended pins as do a standard ATX v2 PSU.
    – sunnyimran
    Nov 27, 2018 at 20:22

1 Answer 1

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In my case I am assuming the problem that some PSU's wouldn't Power ON or wouldn't stay Powered ON without at least some load on its output rails. So I found the solution from an article about turning PC PSU to workbench power supply.

PSU Power Connector Pins that I used

1- Basically I've connected pin 16 (power on) to pin 15 (ground), (GREEN wire to GND) by a switch or it can be shorted permanently

Please note that Green Wire (Power ON) is at different location on ATX 20 pin connector and ATX 24 pin connector.

Power ON Green Wire is on pin 14 on ATX 20 pin connector while Power ON Green Wire is on pin 16 on ATX 24 pin connector PSU's

2- put a 30 Ohm 10 Watt resistor (in picture it is 5 Watt) across pin 4 (+5V rail) and pin 3 (it's ground rail), This is what lets PSU assume that there is some load on the +5V rail. Resistor will get little hot. To truly fake the PSU assume that it is serving some load similar to motherboard, multiple resistors must be used on all PSU output rails according to their voltage/Amps ratings to produce some load on power rails. Some PSU would actually regulate correctly when their outputs are between some specific load ranges and ambiguous regulation when rails are freely open. Some PSU's would rather Power ON and immediately turn OFF when they see no load.

3- put an indicator LED. Connected the positive lead of my indicator LED through a 330 Ohm resistor to pin 8 (power good) and the negative (black) lead to pin 7 (ground).

Now my secondary PSU is working fine.

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