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Archived from groups: alt.sys.pc-clone.dell,comp.sys.ibm.pc.hardware.systems (More info?)
I'm working with a friend to try and resolve a problem with a Dell
Dimension 2400 PC: the system will not power-on.
In an earlier phone call to Dell, my friend was told that the problem
was either a bad power supply or a bad motherboard. The system was out
of warranty, so my friend ordered replacements for both components.
Those components arrived a couple days ago, and my friend asked me to
help install the parts, which we completed earlier today. Much to our
surprise, the system still refuses to power up.
We do see a green pilot light on the motherboard (the LED is located
adjacent to the motherboard's main power connector). But the four
diagnostic lights on the back of the system remain unlit.
We tried the power supplies on a second (non-Dell) PC; that PC seemed
to work just fine with both of the Dell power supplies.
We've swapped the CPU in the Dell with an equivalent CPU chip from
another system; the Dell still refuses to power on.
We've tested the Dell's power switch using a digital multimeter; it
appears to be functional. When the button is pushed in, we get zero
ohms resistance; with the button released, we get infinite resistance.
At this point, we can't figure out what the problem might be. Reaching
the "grasping at straws" stage, we started poking around the non-Dell
system and found one interesting difference between the two boxes: on
the non-Dell PC, we measured 3.3 volts between the two motherboard
power-switch jumper pins. On the Dell, we measured 1.3 volts between
the same two jumper pins.
We've started wondering if this anomaly might be the source of our
problem. Since the 2400 uses an ATX motherboard and power supply, we
assume that the power-on sequence is triggered when the motherboard
(or the power supply) sees a jump of 0 volts to some non-zero value,
caused when the power button is pressed. We're wondering if this
circuitry expects to see some minimum voltage level in order to
recognize that the power switch has been pressed; 3.3 volts seems like
a reasonable value, since that's one of the voltage levels coming out
of the power supply. If our measurements are correct, then we're
guessing that 1.3 volts might not be large enough to trigger the
power-on sequence.
If our guess is correct, our next question would be: any ideas on what
could be causing the under-voltage condition?
Thanks in advance for any help you can offer!
Eric
I'm working with a friend to try and resolve a problem with a Dell
Dimension 2400 PC: the system will not power-on.
In an earlier phone call to Dell, my friend was told that the problem
was either a bad power supply or a bad motherboard. The system was out
of warranty, so my friend ordered replacements for both components.
Those components arrived a couple days ago, and my friend asked me to
help install the parts, which we completed earlier today. Much to our
surprise, the system still refuses to power up.
We do see a green pilot light on the motherboard (the LED is located
adjacent to the motherboard's main power connector). But the four
diagnostic lights on the back of the system remain unlit.
We tried the power supplies on a second (non-Dell) PC; that PC seemed
to work just fine with both of the Dell power supplies.
We've swapped the CPU in the Dell with an equivalent CPU chip from
another system; the Dell still refuses to power on.
We've tested the Dell's power switch using a digital multimeter; it
appears to be functional. When the button is pushed in, we get zero
ohms resistance; with the button released, we get infinite resistance.
At this point, we can't figure out what the problem might be. Reaching
the "grasping at straws" stage, we started poking around the non-Dell
system and found one interesting difference between the two boxes: on
the non-Dell PC, we measured 3.3 volts between the two motherboard
power-switch jumper pins. On the Dell, we measured 1.3 volts between
the same two jumper pins.
We've started wondering if this anomaly might be the source of our
problem. Since the 2400 uses an ATX motherboard and power supply, we
assume that the power-on sequence is triggered when the motherboard
(or the power supply) sees a jump of 0 volts to some non-zero value,
caused when the power button is pressed. We're wondering if this
circuitry expects to see some minimum voltage level in order to
recognize that the power switch has been pressed; 3.3 volts seems like
a reasonable value, since that's one of the voltage levels coming out
of the power supply. If our measurements are correct, then we're
guessing that 1.3 volts might not be large enough to trigger the
power-on sequence.
If our guess is correct, our next question would be: any ideas on what
could be causing the under-voltage condition?
Thanks in advance for any help you can offer!
Eric