PSU - Power Supply Unit

  sschsu 14:27 15 Jul 2005

I tested my new PSU unit on the stand alone mode (ie not connect to the motherboard) and the fans do nor work when the power is switched on. Can anyone confirm that the fans will only work when connected to the motherboard and the PC is switched on. Thanks.

  woodchip 14:35 15 Jul 2005

You may have fried the PSU as it only works when it's got a Load connected. It's called a Power Switching Transformer. And should be connected to a Motherboard or a Dummy load.

  Danoh 14:39 15 Jul 2005

There is more than one fan in a PC, but all require electricity to run and if they do not get supplied via a wire directly or indirectly from the PSU, they can not work.

Some fans connected via the MoBo will still not run even if the MoBo is connected to the PSU as they are governed by temperature sensors, etc.

  sschsu 16:50 15 Jul 2005


It is the 2 fans on the PSU I am talking not the other fans in the PC as suggested by Danoh.

  Diemmess 17:13 15 Jul 2005

The on/off function of the PSU is usually controlled by a low voltage signal from the main panel switch and motherboard, all in circuit.

In effect by trying the PSU to the mains alone. you haven't made a switching circuit.

The only safe way to test it is in the 'box' with case connections made to the mobo.
If it saves trouble, you don't have to connect HD floppy or CD devices.

  DieSse 20:05 15 Jul 2005

Diemmess is qute correct - it's the motherboard that switches on the PSU. The switch on the cabinet supplies a signal that tells the motherboard to turn on the power.

So nothing at all is meant to happen by just plugging in and turning on the mains switch.

Just to make it crystal clear.

  GRFT 07:37 16 Jul 2005

As already mentioned, this so-called "stand alone" mode test could zap your PSU. For a description of what happens click here

  sschsu 17:46 16 Jul 2005

Thanks everyone. Like to replace my existing PSU because the fan is very noisy. Just to make sure that the new PSU needed to connect to the motherboard before the fan works. My current PSU works differently, i.e. when I switch the main power on the fan on the PSU is switched on without the PC being booted up.

  Diemmess 18:06 16 Jul 2005

That is unusual. What age or construction is it?

  Fruit Bat /\0/\ 19:00 16 Jul 2005

click here

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