Q. What am I supposed to do when DC output does not come out
after AC input is turned on? (How to specify the cause)
the case that output does not come out after AC input
is turned on, there are several causes as below.
The largest difference is that main connector shape and output
voltage of secondary output which is connected to PC. Table below shows the
difference in comparison.
(1) No output at all
For ATX power supply, all
outputs except for 5VSB stay halted when AC is turned
on. In order to turn on all outputs, short pin 14 and
pin 15 for 20Pin connector, or short pin 16 and pin
17 for 24Pin connector. Pin 15 of 20Pin and pin 17 of
24Pin connector are both COM level.
In the case
that output voltage is measured with single power
supply, make sure to pass the current at or greater
than the minimum current value; some products may not
work steadily if the current is smaller than the minimum
load current. Many of our products have the minimum current
In general, the procedure above, (pin 14 goes to COM level),
is done at motherboard side when 20Pin connector is
connected to motherboard of ATX.
function allows power supply to be turned on by manually pressing
a soft switch of motherboard manually.
switch is located on the front panel of PC. It, also,
allows power supply to shut down when shutdown process
is completed on Windows 2000/XP,etc.
When output of single power supply is measured, all output
is OK but, when the power supply is connected to motherboard,
the power supply becomes out of work;
・ Output is halted due
to overcurrent detection
・ Mismatching of PS ON signal voltage level
Mismatching of P OK signal voltage level
The above are regarded as
(2) Output voltage is unstable, or low.
Min. load is
required. Let's take PCSA-300P-X2S, for example, it
requires min. 2A load for 5V output. This phenomenon comes
from cross-regulation system. As the load current of 5V is normally
2A, it does not cause the problem. However, when output
voltage is checked with single power supply without load,output
voltage comes to fail. If output voltage is checked
with single power supply, put specified min. load.
cause may be overcurrent detection. Check if there is any
shortage or near shortage in your system. In addition, when
the load exceeds specified load current, output comes to stop
due to overcurrent protection as well.
Furthermore, when fuse is melted, output voltage does not
come out. In this case, repair is required.