Is my Power Supply Bad or my Motherboard???

  • Thread starter Thread starter Sean
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Sean

I have a Dell Dimension 4600 that decided to stop working last week.
When the power button is pushed, nothing happens. I have done the
following to troubleshoot the problem so far:

1) I did a continuity check on the on/off switch - good
2) I reseted all the power connectors to the motherboard and on/off
switch - good
3) I did some voltage checks at the power supplies (ATX type) main
connector. I got 5V on pin 9 (standby power) and 5V on pin 14 (power
on - active low signal). So, I jumpered pin 14 to ground and the fan
on the power supply started to spin.

My question is, does this sound like a power supply problem or a
motherboard problem? I think the wake-up circuit on the motherboard is
powered from the stanby power (pin 9) and that seems to be there so I
would think that I would see something when the on button is pushed.
Then again, the voltage checks I was doing on the power supply was not
loading it down in anyway...

Any one with some experience in this area, I would appreciate your
help!
-Sean
 
I have a Dell Dimension 4600 that decided to stop working last week.
When the power button is pushed, nothing happens. I have done the
following to troubleshoot the problem so far:

1) I did a continuity check on the on/off switch - good
2) I reseted all the power connectors to the motherboard and on/off
switch - good
3) I did some voltage checks at the power supplies (ATX type) main
connector. I got 5V on pin 9 (standby power) and 5V on pin 14 (power
on - active low signal). So, I jumpered pin 14 to ground and the fan
on the power supply started to spin.
Click to expand...

If you do that again, measure the voltages- 5V, 12V on a
drive plug, and 12V on the 4-pin 12V connector.

My question is, does this sound like a power supply problem or a
motherboard problem? I think the wake-up circuit on the motherboard is
powered from the stanby power (pin 9) and that seems to be there so I
would think that I would see something when the on button is pushed.
Then again, the voltage checks I was doing on the power supply was not
loading it down in anyway...

Any one with some experience in this area, I would appreciate your
help!
-Sean
Click to expand...

The checks thus far are better at finding a fault rather
than ruling one out. I presume you have unplugged the PSU
from AC for at least a couple minutes... if not so do, or if
you had, do it again and clean the CMOS while it's
unplugged.

Had anything about the system changed, hardware or even that
it was scooted across the desk? Recheck all cables, but
also cards, memory, and if anything looks a little
misaligned try removing and reinstalling that part.

If no luck so far, unplug the drives and other misc
accessories from power and data cables.... this while system
is disconnected from AC of course, then retry the system.

Do you have any spare parts, perhaps a power supply or video
card? Examine the motherboard and video card for failed
capacitors. A strong light might help.

What's a 4600 like, all major parts? Has the system been
changed from it's original configuration?

When you measure the voltage, the preferred way is to leave
the connector plugged into the motherboard and use long
probes to (carefully) measure in through the back of the
connector. Better to use needle-tips rather than piercing
probes, IMO, as the metal contact is easily accessed inside
the back of the plastic ATX connector shell. Also, you can
measure the PS-On signal prior to pressing the power button
then _while_ pressing it. If the motherboard power-on
circuit is operational it will pull the signal low (voltage
decrease).

If all else fails begin stripping the system down- unplug
all parts but CPU, heatsink/fan, 1 memory module and video.
Unplug keyboard, mouse, drives, cards, etc... Short the two
power-on pins together to start the system unless you're
_sure_ the front panel wiring and switch (since they're
probably all in one integrated connector block?) are ok...
better to just unplug them all to isolate things even more.

You could leave the PSU unplugged from AC for a few minutes
then open and inspect it, but if you weren't already prone
to do it, don't power on while open and there probably
aren't any other tests you should do inside.

Lots of variables since we don't know 100% about the system
but your initial impression is still viable, that odds are
it's the board or power supply. You can put a bit of a load
on the power supply by leaving it plugged into your drives
when you short the PS-On pin to ground on the ATX connector,
just be sure you have the right pins as some Dells used
non-standard power supplies.
 
I have a Dell Dimension 4600 that decided to stop working last week.
When the power button is pushed, nothing happens. I have done the
following to troubleshoot the problem so far:

1) I did a continuity check on the on/off switch - good
2) I reseted all the power connectors to the motherboard and on/off
switch - good
3) I did some voltage checks at the power supplies (ATX type) main
connector. I got 5V on pin 9 (standby power) and 5V on pin 14 (power
on - active low signal). So, I jumpered pin 14 to ground and the fan
on the power supply started to spin.
Click to expand...

What happens to PS_ON# when you depress the power switch on the front
panel? Since you say nothing happens, then I'm assuming PS_ON# remains
high. That means that either the motherboard circuitry is bad, or the
front panel power switch is not connected properly to the motherboard.
Try measuring the level of the PowerSwitch pin at the front panel
connector header on the motherboard when you depress the power button.
 
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