supervinx wrote in
:

Il Tue, 30 Mar 2010 21:14:04 +1100, Phil Allison ha scritto:

"supervinx"


I've little experience in switching PSUs ... I've one of them (coming
from an Amiga 2000) which shuts off at the first load.
With no load at all, it delivered 5.9V out of 5 nominal.

** Many PC type switching PSUs need a load to be applied on ALL the
outputs on order to work properly.

Why not apply load resistances ( not incandescent lamps either) to each
DC rail and see if it holds up then ??

scope each rail to see if they rise proportionally.


Thing is, when you load just the 5 volt rail, the other DC rails go UP
in voltage - and that may trigger the out of range voltage detector
circuit and stop the whole damn show.



.... Phil

The PSU shuts off under normal operations while connected to his MB. I
connected it to an external HD (load on both +5 and +12): I see the
voltage raising and the voltage detector shutting the PSU down.
I have no oscilloscope handy ... with a digital multimeter I can see the
+5 rising about 4.8, the +12 about 9 and then stop.

A DMM will not respond fast enough.

The main capacitors are 200V rated, but I see 215 across them


By "main caps" do you mean the line supply filter caps,right after the
rectifier? The raw DC supply for the switcher?
If it's a doubler,you should have around 300VDC,if a single-ended
rectifier,about 170VDC. Perhaps you don't have enough input DC.
Or maybe you're seeing some AC along with the DC.

Many SMPS use a cap-rectifier doubler for 120 VAC operation,and a switch
changes it to single-ended for 220VAC operation.

--
Jim Yanik
jyanik
at
localnet
dot com