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


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