From: nospam@needed.invalid   
      
   On Fri, 7/18/2025 3:29 AM, Edmund wrote:   
   > On 7/16/25 16:50, pinnerite wrote:   
   >> I connected a brand new Asus Tuf 850W PSU to an ASUS motherboard with   
   >> just the processor and heatsink installed, in a MIDI Tower case.   
   >>   
   >> The PSU was not in the case.   
   >>   
   >> Switched on and...   
   >>   
   >> Nothing happened.   
   >>   
   >> I detached the PSU and attached a small tester to it.   
   >> Powered on ...   
   >>   
   >> No sign of life.   
   >>   
   >> What can cause a PSU to die under those conditions?   
   >> Surely it has inbuilt protection against overload.   
   >>   
   >>   
   >>   
   >>   
   > What comes to mind is, it didn't die but doesn't switch on.   
   > There might be a electrical check that isn't happy.   
   > Are you sure you connected all plugs and cables to the mainboard?   
   >   
   > As usual, if everything else fails, read the manual.   
   >   
   >   
      
   ATX PSU are pretty simple.   
      
   1) Switch on at back.   
      Check the +5VSB pin for 5V output. The PSU cannot   
      start, unless 5V is present on the +5VSB pin.   
      
      When sitting idle like that, and without Alans PSU tester   
      plugged in, the +5VSB pin and the PS_ON# pin should both have   
      the same five volt voltage on them.   
      
   2) Ground the PS_ON# pin. This turns on the main rails   
      3.3V, 5V, 12V. Fans should spin. If a cooling fan only   
      "twitches", then the PSU is cutting out on overcurrent.   
      You can connect a couple cooling fans you have fitted   
      with Molex, to work as "indicator loads" for such a test   
      outside of the computer case. I have a few fans with   
      Molex on them.   
      
   While the PSU have a slow blow fuse inside the housing,   
   those almost never trip. You can use your Kill-A-Watt meter,   
   cable up the PSU, and if absolutely no current at all is   
   drawn under any circumstances, THEN it could be an open fuse.   
      
   While this circuit is not up-to-date with the latest practice   
   (this circuit does not use double forward conversion), a lot   
   of the elements in here are still the same. This will help   
   you understand a bit of the circuit behavior.   
      
      http://www.pavouk.org/hw/en_atxps.html   
      
   For example, NTCR1 on the left, is the inrush limiter. The PSU   
   on the computer across from me, has a relay in that circuit.   
   The relay closes and shorts out NTCR1 so there is no voltage   
   drop across it, when the PSU is fully charged (inrush charging).   
   So while the pavouk shows *some* solution for inrush, it might   
   not be exactly the same as the more sophisticated modern approaches   
   to inrush limiting. You can use the power factor correction circuit,   
   for inrush limiting too. (That was a fad for a few years.)   
      
       Paul   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)