PSU tester -5V not lit

[Naujoks]

I have trouble with a 'be quiet 530w' PSU.
The PC I was using it was unstable and the power cut out, so I checked the PSU with my PSU tester, and with the main power connecter the -5v light was not on, so I RMA'd that PSU. Got a new one back, tried the tester on it, just for fun, and the -5v is not on!
Are there any situations where that line is supposed to be off? Could it really be that two new PSUs should be faulty from the start?

 

[delluser1]

-5v is no longer a part of the ATX spec., and was optional for quite a few years, many power supplies don't have it.
Have you looked at the 24 pin main connector to see if there is a missing pin ?
http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain24

 

[Naujoks]

Thanks for the info, the computer I put together wouldn't switch on at first, then I took the mobo out and put it next to the case, but still connected. It switched on. I screwed it back in, would constantly cut out and come back on.
Thought it was the mobo, swapped it for another one, same problem. Swapped the psu and it's been stable ever since.
Now got the psu I RMAd back and have yet to put it into a new PC.