Doomed said:
A few days ago a storm came through and kicked the power off for a few
hours. There was no lightening strike involved close by to the best of
my knowledge mostly wind.
I have one pc {Dell Inspiron i537-3492} hooked up to an expensive ass
a.p.c. 500 ( Its surge protection plus battery back up) unit
and the other {eMachine} hooked up to a cheap ass bar unit surge
protecter only.
Go figure the "Dell" is the one that will not power on now. The reset
button only slides from left to right as far as I can tell. I've un
plugged it and let it sit for a day and tried to power on with the
reset in both positions and it will not power on. There is a green
light just below the reset button. It's on when you have it plugged
into the wall and goes off several seconds after you unplug it.
I have the side panel off. I see no visible fuses or breakers. I'm
guessing taking out the power supply is next but I am waiting for some
advise before going any further.
I hope I can fix this my self with a little help from you guys.
YIA,
DS
p.s.
and yes... when testing I am pluging directly into a "confirmed
working outlet".
I don't see a lot in the way of controls on that thing.
http://img29.imageshack.us/img29/1551/inspiron537.gif
http://support.dell.com/support/edocs/systems/insp535mt/en/sm/index.htm
And I don't see a "reset" slider here. There is a jumper for clearing
the password. And another jumper for clearing the rest of the CMOS RAM
(256 bytes of parameters, which store BIOS settings of one sort or another).
http://support.dell.com/support/edocs/systems/insp535mt/en/sm/techov.htm#wp1200202
*******
The green LED on the motherboard, should be connected to +5VSB from the
power supply. The power supply consists of two parts (like, two separate
regulators).
AC ---- HVDC ------ 5VSB regulator
------ Regulator for 3.3V, 5V, 12V main rails
If you want to see a PSU in more detail, to see what I'm talking about,
there's a full schematic of one, here.
http://www.pavouk.org/hw/en_atxps.html
So if the green LED comes on, that means the fuse isn't blown
in the ATX supply. And a portion of the supply (+5VSB) is working.
For the motherboard to turn on the system, it has the following.
+-------------+
PSU --- +5VSB -----------| |
| Motherboard |--- PS_ON# ---> back to PSU
Power_button_on_front ---| |
|
If the motherboard was severely damaged some how, such that it couldn't
send PS_ON#, that would prevent it from starting.
If the power supply is damaged on the PS_ON# input, then that
could stop it. Some power supplies become "deaf" to their PS_ON#
input, and it doesn't matter whether logic 0 or logic 1 is
sent to the supply - nothing happens. And that would be a
dead supply.
To test the supply, we'd normally pull it (making a diagram of where
all the wires go, and what color wire is on which side of the connector).
Then, using a paper clip, we'd connect PS_ON# to COM. That would be
performing the same function as the motherboard was performing,
namely, pulling the PS_ON# signal towards ground or zero volts.
If the PS_ON# signal is floating, it floats up to a 5V potential.
And to turn on the main rails, the motherboard "tugs down" on the
PS_ON# signal, sinking a couple milliamps, and the logic low level
on PS_ON# tells the supply to start, spin the power supply fan, and
so on.
The wiring information for a 24 pin supply is here, page 37. You could
test the power supply, stand alone, by connecting pin 15 to 16
(black and green wires). Any black wire would do, but 15 is pretty
close to 16. The "best practices" recommendation, is to have a
dummy load connected to the supply, when connecting pin 15 to pin 16.
If you have an old disk drive, that would be an example of a dummy load.
(If I don't mention that, someone will only complain
) The idea
of the dummy load, is to draw an ampere or two from some rail on the
supply, as the supply is not push-pull in design, only pushes, and
a slight load performs the pull function and helps keep the supply
regulated. I've not had a problem here, testing without a dummy load,
but I have to mention the dummy load for sake of completeness. Some
supplies, on the label, actually mention they have a minimum load spec.
I no longer see supplies with such a crappy design feature.
http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf
So your progress so far, is
1) Green light = good. Means +5VSB is present. That should power
enough of the motherboard, for the motherboard to assert PS_ON# to
ground level, when the front bezel power button is pressed.
2) Either the power supply is not responding to PS_ON#, or the motherboard
is no longer capable of sending PS_ON# to the supply. We can't be sure
which has failed.
If you owned a multimeter, you can probe the 24 pin connector, while it
remains connected to the motherboard. You set the multimeter to volts,
like 20V full scale, and clip the black lead to the chassis. The chassis
is grounded, same potential as any black wire on the harness. Clipping
onto the chassis, is to avoid the danger of shorting something. I use a
shiny screw, like on a rear I/O connector, for my electrical connection.
With the red lead, you can touch the exposed metal, which sits just
inside the plastic shell of the 24 pin connector.
Start from power off at the back of the computer. (Note - do *not* change
the 115V/230V slider on the supply!) Turn on the power at the back of
the computer. The green LED should come on. With the multimeter, verify
pin 9 (purple, +5VSB) reads 5.0 volts. Now, check pin 16 (green, PS_ON#)
as well, and it should be very close to the same 5.0 volt value. Next,
press the front panel power button. Go back to pin 16 (green, PS_ON#)
and verify the voltage is very close to 0.0 volts. Acceptable, might be
less than 0.8V or so. If it's riding around 2.0V, then the motherboard
is having a problem pulling the signal all the way to ground. Closer to
zero volts at that point, would be better.
Anyway, post back, report your pin 16 readings.
The power supply also has a status signal, PWR_OK on pin 8. That's only
important if the power supply fan is spinning. It's possible, for the
power supply to withhold PWR_OK, even if the power supply fan is spinning.
The computer can't boot, until the power supply says it is OK to boot.
But that's not even a consideration (don't need to measure it), unless
the power supply fan starts to spin. The status is only important,
if you get as far as the main rails come on, and the 3.3V, 5V, 12V
are present, and the motherboard still won't run. In such a case,
you could then check PWR_OK and see if the state indicated it was
ready to run. The motherboard has its own internal "I'm OK" logic as
well, but tracing that down is a lot tougher.
Without a multimeter, about all you can do, is pull the supply, and
connect PS_ON# to COM for a test, with the switch on at the back
of the supply. If the fan spins, the supply could be OK, and maybe
the motherboard has a problem. If the fan doesn't spin, then maybe
the main portion of the ATX supply is bad. That's about the best
we can do, in terms of diagnosis without a multimeter. Using
the multimeter, if the chassis isn't too crowded, might be
a bit easier than pulling the supply, if you haven't done it
before. The multimeter can't tell the whole story, except
in certain cases (like, you see a good level of zero volts
on PS_ON#, 5.0 volts on +5VSB, and the supply still won't start,
in which case the second half of the supply is bad).
Another small note - in the event the computer will not respond
to the front power button, you switch it off at the back for one
minute, then switch it on again. Certain faults detected inside
the computer, are "latching" type. To clear the latching faults,
you remove all power from the computer and let it drain. And then,
it should be "re-armed" to detect faults again. I think you've
already done that, but again, I have to mention it. Letting it
drain, is going to happen when you do your tests above anyway.
Paul
