wasbit wrote:
"RainbowMan" wrote in message
...
I reset the bios and reflush Dell the PSU and MB( because some
voltage still left over even though I completely turned off the system
as some online user recommend) and tried again it was working again. I
thought I fixed finally but the next morning I turned on again this
time it is completely dead. But the PSU still ok and the MB is ok
too. I am using 24-pin other PSU and no problem.
Only adjustment is I converted 4-pin PATA pinout to 15-pin SATA
(since this PSU only has 2 SATA cable) and the strange thing is
Windows reported SATA drive as PATA drive I guess since the 3.3V
orange wire is unconnected.
I read, a long time ago, that holding the power button in after
isolating the power, drains the charge in the capacitors.
Whether this is true, I don't know, but I've done it ever since.
The power drains on its own too.
It depends on which "edge" of the power signal
which is latched, as to when the draining occurs.
5---------------------
\ +5VSB voltage
0 \
----+ +---------
| | \ Front panel button
+------+ \ (low is active)
-----------+
| PS_ON# (low is active)
+-----------xxxx no-drive when no-5VSB
starts to drain
There are two converters running off a common 300V+ capacitor.
The +5VSB converter is always running when
the switch at the back is on.
After about 30 seconds, the +5VSB drains on its own
when there is a loss of AC.
Pressing the front panel switch and releasing,
starts the main converter running. It cannot
run for too long, since the caps have limited
holdup time (16msec maybe at full load).
The main converter may die out first, as at
some point there isn't enough 300V+ left
to operate it.
Or, the PS_ON# transistor may lack the ability
to keep PS_ON# at zero volts.
The +5VSB is probably the last one to wink out.
This changes the +5VSB discharge time from 30 seconds
to a couple seconds.
Since no active element clamps 3.3,5,12V outputs,
we can't say with certainty what residual voltage
is present. The VCore motherboard converter would
tend to drain +12V to maybe +6V. The VCore converter
does not run all the way down to zero volts.
The informal evidence, is the secondary outputs
drop to zero pretty well, without needing any
additional help from users.
So while pressing the button accelerates the
process a bit, in the end the result is about
the same. You save about 28 seconds of the
sequence.
On Asus motherboards, a green LED on the motherboard
is tied to +5VSB. When that LED goes out, it is
safe to work on the PC inside. Other brands
do not have this. For the brands that do not
have this, pressing the button reduces
the wait time, but the multimeter is
your best bet for determine +5VSB is gone.
There is a schematic showing the two halves of a
supply, here. But this does not show the motherboard
logic that controls PS_ON#. PS_ON# comes in around
the middle-left of the schematic.
http://www.pavouk.org/hw/en_atxps.html
Paul