i have an ancient AT psu, but it causing problems. I planned to use it to test fans, drives, and stuff like that. however, when i hook it up to a fan, it doesnt power that fan on properly. the power it suplies stutters. instead of the molex 4-pin fans i hook up to it just beign on, they turn for a second then stop, then if im lucky start that cycle over. it supplies power on and off, then simply supplies no power whatsoever. i don't it realises it should be on, as the psu fan doesnt even spin either.
basically, what i mean is: why does it supply power for a sec when i press the power switch on the psuthat used tobe attached to front of the pentium 1 166mhz machine it was previously in only turn on the psu on for a second? is it not detecting enough load?
Maybe, maybe not. What does it do when it's connected to a PC? If it does the same thing, there's a very good chance the PSU is dead. If it runs and sounds OK,it probably means there wasn't enough of a load on it.
PSU's require a certain minimum load on them and sometimes the fan isn't enough.
It took me a couple of readings, but I agree with jsc- he got the right message form OP's post, and I think he got the right answer. It is likely the old AT PSU is not putting out the right 12 VDC power to fans simply because the load is too small to regulate, AND there is NO load at all on the other rails, like +5 VDC.