> I tried building a device into a PC which was powered from 
> the +5V line on one of the disk drive power connectors, and 
> found that it was very unreliable in starting up - more often 
> than not it didn't!
> 
> So I put a meter on the connector and found that when the PSU 
> has mains connected, but is turned off, there was 1.8V on the 
> 5V line, so powering the PC down and up does not power the 
> device I mentioned down properly.  From cold it seems to work 
> if you connect the power lead and then press the power-button 
> within a couple of seconds - more than that and it locks up 
> the device.
> 
> I tried another PSU and that was showing 0.8V and had the 
> same problem.  I know there is a separate 5V Standby supply, 
> but I would have thought that the main 5V should drop to zero 
> when power is off, shouldn't it?
> 
> Has anyone else encountered this?  Am I likely to find a PSU 
> that does behave "properly"?
> 
> If not I'll have to use the +12V and put my own 5V regulator 
> in-line, which will be annoying but will solve it (the +12V 
> line does drop to zero).
> 
> Cheers,
> 
> 
> Howard Winter
> St.Albans, England


You need to put a load on the 12V rail, it won't start up otherwise.  

A lot of people put a 10W resistor across it so it draws a half amp or so.
A light bulb works too.  Occasionally I'll just plug in a old hard drive.

Tony

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