Computer won't start


M

Metspitzer

I have an XP machine that was working fine last night when I shut it
down. It would not start this morning. I pulled the side off. The
mobo ready light burns. I unplugged the power supply from both mobo
connection and re seated them. When I push the power button, the CPU
fan rotates for just an instant.

I hear no hard drive. I have seated the memory and checked all the
mobo to case connections. There is no mobo beep.

What can I check next?
 
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S

SC Tom

Metspitzer said:
I have an XP machine that was working fine last night when I shut it
down. It would not start this morning. I pulled the side off. The
mobo ready light burns. I unplugged the power supply from both mobo
connection and re seated them. When I push the power button, the CPU
fan rotates for just an instant.

I hear no hard drive. I have seated the memory and checked all the
mobo to case connections. There is no mobo beep.

What can I check next?

Does the power supply fan start up? If not, that may be your problem; most PS won't come up if the fan doesn't start
first. Or the PS itself may have died. The ready light is just a small part of what it does.

Unplug the AC cord from the back of the computer or from the wall, whichever is easiest. Leave it unplugged for about a
minute, then plug it back in. Does the PC start now?

When you turn it on, does the keyboard light up?

Unplug everything that's not necessary, like printers, external drives, etc. Also unplug any CD drives internally. Did
that help?

Is this a newer machine, maybe still under warranty? Have you ever had a problem before? If it's an older machine, have
you ever changed the CMOS battery? If not, you might try a new battery, although that's probably not it.
 
F

Flasherly

I have an XP machine that was working fine last night when I shut it
down. It would not start this morning. I pulled the side off. The
mobo ready light burns. I unplugged the power supply from both mobo
connection and re seated them. When I push the power button, the CPU
fan rotates for just an instant.

I hear no hard drive. I have seated the memory and checked all the
mobo to case connections. There is no mobo beep.

What can I check next?

Swap out a PS first if you've a spare. Reseat, try different memory
seatings or denominations. Start removing components - down to MB/PS/
VID if necessary. Start with DVD and HDs, try booting between each
removal. Vid card, a rare culprit, is next to last last -- the MB
ground connects. The MB that boots on a piece of foam or cardboard
once removed has grounding issues. If MB capacitors at all then
figure in as problematic, be careful -- worse case is bad caps can be
doing two things 1) killing PSupplies prematurely, 2) running up extra
electricity bills by as much as $20 a month. If it's caps and you
manage to continue, it'll just get worse.
 
S

Sjouke Burry

I have an XP machine that was working fine last night when I shut it
down. It would not start this morning. I pulled the side off. The
mobo ready light burns. I unplugged the power supply from both mobo
connection and re seated them. When I push the power button, the CPU
fan rotates for just an instant.

I hear no hard drive. I have seated the memory and checked all the
mobo to case connections. There is no mobo beep.

What can I check next?

Had about the same a few weeks ago.

Turned out to be a failed power button.
That was a rather cheap repair, 59 Euros,
including a new DVD ram unit.
 
F

Franc Zabkar

I have an XP machine that was working fine last night when I shut it
down. It would not start this morning. I pulled the side off. The
mobo ready light burns. I unplugged the power supply from both mobo
connection and re seated them. When I push the power button, the CPU
fan rotates for just an instant.

I hear no hard drive. I have seated the memory and checked all the
mobo to case connections. There is no mobo beep.

What can I check next?

I suspect there may be a short circuit on one of the supply rails. Use
a multimeter to measure the resistances on the +5V and +12V supplies.

A common culprit is a TVS diode on one of the hard drives, in which
case the fix may be a simple one.

- Franc Zabkar
 
P

Paul

Metspitzer said:
I have an XP machine that was working fine last night when I shut it
down. It would not start this morning. I pulled the side off. The
mobo ready light burns. I unplugged the power supply from both mobo
connection and re seated them. When I push the power button, the CPU
fan rotates for just an instant.

I hear no hard drive. I have seated the memory and checked all the
mobo to case connections. There is no mobo beep.

What can I check next?

The twitch on the CPU fan, means the power supply detected an overload.

For the first 35 milliseconds, overload detection is disabled on
a thing like an ATX supply. That's to give time for any capacitors
to be charged up. Then, the power supply starts looking for an overload,
and will disable the output if it sees a problem. The 35 milliseconds
of power, is what makes the fan twitch.

The problem is either a "real" short circuit, or, the power supply
is weak, and is interpreting a normal load as an overload.

In some cases, this can be caused, by a visiting kid switching the
red "110/220" slider on the back of the supply from 110 to 220.
Switching it the other way (220 country, switch to 110) might
cause it to explode :) But in a 110 country, switching to 220
might cause the supply to behave "weakly".

Paul
 
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J

John Doe

Six replies to the original post within eight hours. Nothing
inactive about this group :)

Same in some other groups. Only certain groups have taken a big
hit in the last few years or so. Strategy gaming is one. But I
recall starting out in the WarCraft group. The WarCraft real-time
strategy (RTS) group and its parent strategy group are pretty much
dead, but those might have been born to games that did not at the
time have web based discussion forums like they do nowadays.

There are many groups like woodworking, metalworking, electronics,
and others that are thriving. I think the serious topics will
always remain on UseNet.

Just my observation, not a bone of contention here.

Good luck and have fun.
 
L

Loren Pechtel

I have an XP machine that was working fine last night when I shut it
down. It would not start this morning. I pulled the side off. The
mobo ready light burns. I unplugged the power supply from both mobo
connection and re seated them. When I push the power button, the CPU
fan rotates for just an instant.

I hear no hard drive. I have seated the memory and checked all the
mobo to case connections. There is no mobo beep.

What can I check next?

My vote: You have a bad power supply. Note that in this case a power
supply tester will *NOT* show the problem.

What I think is going on here is the power supply can't deliver enough
juice anymore to cover the starting surge. The voltage doesn't
stabilize in time and the deadman circuit kills it. It has no problem
delivering enough for the tester, though.

To test this: Shed every watt you possibly can and try it. Unplug
the power connectors from the drives and any USB devices, if that's
not enough unplug any cards it's possible to POST without.

Alternately, if you have a supply lying around, swap it and see what
happens.
 
M

Metspitzer

My vote: You have a bad power supply. Note that in this case a power
supply tester will *NOT* show the problem.
Considering I don't have a power supply tester that is not really bad
news. I do have another power supply and I intend to give that a try
very soon. All I lack is motivation.

Thanks
 
M

Metspitzer

Considering I don't have a power supply tester that is not really bad
news. I do have another power supply and I intend to give that a try
very soon. All I lack is motivation.

Thanks
The power supply I plan on using is in a machine that has just lost
it's hard drive for the second time. :)
 
F

Franc Zabkar

The power supply I plan on using is in a machine that has just lost
it's hard drive for the second time. :)

The failure modes of the hard drives will give us a clue as to whether
the failures were related to the PSU.

BTW, you can purchase a multimeter for US$5, eg ...

Cen-Tech 90899 7 Function Digital Multimeter:
http://www.harborfreight.com/7-function-digital-multimeter-90899.html

If there is a short circuit on one of the devices, eg HDD, then
powering it up again and again will only risk doing more serious
damage to it. Take some resistance measurements first.

- Franc Zabkar
 
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M

Metspitzer

The failure modes of the hard drives will give us a clue as to whether
the failures were related to the PSU.

BTW, you can purchase a multimeter for US$5, eg ...

Cen-Tech 90899 7 Function Digital Multimeter:
http://www.harborfreight.com/7-function-digital-multimeter-90899.html

If there is a short circuit on one of the devices, eg HDD, then
powering it up again and again will only risk doing more serious
damage to it. Take some resistance measurements first.

- Franc Zabkar

I did unplug all the hard drives and try again. Nothing. No power
supply fan only a bump on the CPU fan.

As several have suggested, when I get motivated I will try another
power supply.

Thanks
 
M

Metspitzer

I have an XP machine that was working fine last night when I shut it
down. It would not start this morning. I pulled the side off. The
mobo ready light burns. I unplugged the power supply from both mobo
connection and re seated them. When I push the power button, the CPU
fan rotates for just an instant.

I hear no hard drive. I have seated the memory and checked all the
mobo to case connections. There is no mobo beep.

What can I check next?

The correct answer was Power Supply. When I changed it with another
power supply, it started.

Every power supply I ever tested (less than a dozen) shows continuity
from hot to neutral. I assume this means the fuse is good. This
power supply shows no continuity from hot to neutral. I have
contacted Antec to see if it is still under warranty, so I don't plan
to open the case. (I think I ordered the PS from Amazon and it seems
that Amazon has lost it's order history)

The thing is, I can't explain how the fan rotated for an instant if
the fuse was bad.
 
M

Metspitzer

Does the power supply fan start up? If not, that may be your problem; most PS won't come up if the fan doesn't start
first. Or the PS itself may have died. The ready light is just a small part of what it does.

Unplug the AC cord from the back of the computer or from the wall, whichever is easiest. Leave it unplugged for about a
minute, then plug it back in. Does the PC start now?

When you turn it on, does the keyboard light up?

Unplug everything that's not necessary, like printers, external drives, etc. Also unplug any CD drives internally. Did
that help?

Is this a newer machine, maybe still under warranty? Have you ever had a problem before? If it's an older machine, have
you ever changed the CMOS battery? If not, you might try a new battery, although that's probably not it.

When I read this message I was at a no posting on Usenet machine.

I have the computer on the kitchen table so most of your suggestions
are not practical to try at the moment. Also, the machine is using a
very large CRT monitor so getting the two back together is a pain.

Thanks for your suggestions.
 
M

Metspitzer

Had about the same a few weeks ago.

Turned out to be a failed power button.
That was a rather cheap repair, 59 Euros,
including a new DVD ram unit.

You must be living right. No way I expect my solution to be that
simple. :)
 
M

Metspitzer

I suspect there may be a short circuit on one of the supply rails. Use
a multimeter to measure the resistances on the +5V and +12V supplies.
I haven't tried this yet, but I did start the computer with the other
power supply with no hard drives.
 
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M

Metspitzer

Everyone that owns a computer should own a PSU tester. Very cheap and
save much time and trouble. PSUs are the most common component
failure.

It might be a good time to get one.
Thanks
 
M

Metspitzer

The twitch on the CPU fan, means the power supply detected an overload.

For the first 35 milliseconds, overload detection is disabled on
a thing like an ATX supply. That's to give time for any capacitors
to be charged up. Then, the power supply starts looking for an overload,
and will disable the output if it sees a problem. The 35 milliseconds
of power, is what makes the fan twitch.

The problem is either a "real" short circuit, or, the power supply
is weak, and is interpreting a normal load as an overload.

In some cases, this can be caused, by a visiting kid switching the
red "110/220" slider on the back of the supply from 110 to 220.
Switching it the other way (220 country, switch to 110) might
cause it to explode :) But in a 110 country, switching to 220
might cause the supply to behave "weakly".

Paul
With nothing connected to the PS but the mobo caused the twitch. If
it was an overload, the new PS should have done the same, right?
 
S

SC Tom

Metspitzer said:
When I read this message I was at a no posting on Usenet machine.

I have the computer on the kitchen table so most of your suggestions
are not practical to try at the moment. Also, the machine is using a
very large CRT monitor so getting the two back together is a pain.

Thanks for your suggestions.
I saw from your follow-up post that it was the PS. Guess I should have stopped there :)

Glad you got it going again.
 
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P

Paul

Metspitzer said:
The correct answer was Power Supply. When I changed it with another
power supply, it started.

Every power supply I ever tested (less than a dozen) shows continuity
from hot to neutral. I assume this means the fuse is good. This
power supply shows no continuity from hot to neutral. I have
contacted Antec to see if it is still under warranty, so I don't plan
to open the case. (I think I ordered the PS from Amazon and it seems
that Amazon has lost it's order history)

The thing is, I can't explain how the fan rotated for an instant if
the fuse was bad.

If the fan "twitches", then you know the primary is intact, and something
is defective on the secondary. To "twitch", there has to be some
transformer action, between the primary and secondary. The switching
transistors on the primary, have to run for a short period of time,
to provide enough energy through the transformer, to make the cooling fan
on the CPU to twitch. The power supply has capacitors on the secondary side,
and they'd need to be charged high enough, to cause the fan motor to start
moving. So it's going to take thousands of switching cycles on the
switching transistors (maybe 35 milliseconds worth), to get that far.

*******

With respect to your testing the contacts on the AC side of the
supply, you'd need to understand how the multimeter does its test,
to understand the results.

For example, look at the primary here, and tell me under what
conditions the input will conduct. Hint - two diode drops into
a capacitor. Does the multimeter provide a high enough voltage
to cause two diodes in series to conduct ? You really need a
good understanding of how the multimeter works, before you
can understand the results. Some measurements are worthless,
because they can be ambiguous. (Double hint - just because
it reads open, doesn't mean its open. It's a function of
what the meter is doing. To remove the ambiguity, you
remove the power supply cover, and ohm out the fuse directly
if you can find it.) In this example, there is that 560K
on the primary side in parallel, and perhaps you can see
that one.

http://www.pavouk.org/hw/en_atxps.html

An ohmmeter is "a voltmeter, in parallel with a
current source with a limited compliance voltage".
And in English, it means the ohmmeter has two "corner
conditions". Into a dead short, the current source won't
put more than the current limit value into the circuit
(like, 1.000 milliamps of test current or 100.0 microamps
of test current). And when open circuit, the current source
voltage level won't rise to higher than the compliance
voltage level. (Perhaps that is 1 volt on a low power ohms range,
for example. My old Simpson analog meter, could apply as much
as 9 volts under similar conditions. My Simpson is the one
that's going to "find the fuse" for me.)

http://www.allaboutcircuits.com/vol_3/chpt_3/2.html

"Beware that some digital multimeters equipped with a "diode check"
function may output a very low test voltage (less than 0.3 volts)
when set to the regular "resistance" (ohm) function: too low to
fully collapse the depletion region of a PN junction. The philosophy
here is that the "diode check" function is to be used for testing
semiconductor devices, and the "resistance" function for anything
else. By using a very low test voltage to measure resistance,
it is easier for a technician to measure the resistance of
non-semiconductor components connected to semiconductor components,
since the semiconductor component junctions will not become
forward-biased with such low voltages."

That's an explanation of so-called "low power ohms" versus
"high power ohms" type measurements. The difference is the first
one, doesn't use a compliance voltage value high enough to turn
on diodes.

A great learning experience, is to connect two multimeters
together. For example, put one of them on "ohms" and the
other on "volts". Or, put one on "ohms" and the other
on "current" (after changing the holes the test leads go into).
The things you read out, should help you better understand
the stimulus the meter is applying to a circuit. And at
least explain, how two meters might reach a different
conclusion.

Paul
 

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