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Bad Power Supply



 
 
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  #1  
Old November 8th 19, 04:16 PM posted to alt.comp.hardware
tb
external usenet poster
 
Posts: 66
Default Bad Power Supply

I have this desktop PC (quite old!) that when I shut it down I have to
wait at least a minute before I can reboot it. If I press the power
button before approx. one minute it does not turn on.

I'm hoping the hardware experts in this group will confirm that it is a
power supply issue, not some component on the motherboard that is
failing...

--
tb
  #2  
Old November 8th 19, 08:46 PM posted to alt.comp.hardware
VanguardLH[_2_]
external usenet poster
 
Posts: 1,453
Default Bad Power Supply

tb wrote:

I have this desktop PC (quite old!) that when I shut it down I have to
wait at least a minute before I can reboot it. If I press the power
button before approx. one minute it does not turn on.

I'm hoping the hardware experts in this group will confirm that it is a
power supply issue, not some component on the motherboard that is
failing...


From when are you measuring the "minute" you have to wait before
pressing the Power button? Are you measuring from when you tell Windows
to shutdown, from when the shutdown screen appears, from when the Power
LED on the case goes out, or from when are you measuring how long to
wait?

Does the fan in the PSU stop when you power down?

When you think the computer is powered down (which is after the fans
stop spinning and the Power LED goes out), can you yank the power cord
from the case, plug it back in, and then power up without waiting?

Saying "old" doesn't say how old or what type of power control the
computer uses. A long time ago, like over 20 years ago, power control
was the AT style. The Power switch was a mechanical switch that
disconnected power from the PSU (which turned off, so everything lost
power). The Power switch went to the PSU. It was like wall switch to
turn off the room lights. Then came the ATX style power control. The
Power switch did not have a direct connection to the PSU. Instead the
Power switch went to the motherboard's power control logic. The Power
switch told the mobo to power down the computer, and then the mobo told
the PSU to power off. This made sure all hardware was in a state that
was prepared to lose power, not just abruptly yank away the power.

https://en.wikipedia.org/wiki/AT_(form_factor)
https://en.wikipedia.org/wiki/ATX

ATX started back in 1995: 24 years ago. So how old is old to you? Does
the Power switch run to the PSU or to the motherboard?

Rather than attempt vague troubleshooting on vague (actually completely
undescribed) hardware, give the brand and model of:

- PSU
- Motherboard

Did you build this computer (did you or someone else fab the computer),
or is a pre-built (you buy it already built)? If a pre-built, what is
the brand and model of the computer?
  #3  
Old November 8th 19, 10:08 PM posted to alt.comp.hardware
tb
external usenet poster
 
Posts: 66
Default Bad Power Supply

On 11/8/2019 at 1:46:43 PM VanguardLH wrote:

tb wrote:

I have this desktop PC (quite old!) that when I shut it down I have
to wait at least a minute before I can reboot it. If I press the
power button before approx. one minute it does not turn on.

I'm hoping the hardware experts in this group will confirm that it
is a power supply issue, not some component on the motherboard that
is failing...


From when are you measuring the "minute" you have to wait before
pressing the Power button? Are you measuring from when you tell
Windows to shutdown, from when the shutdown screen appears, from when
the Power LED on the case goes out, or from when are you measuring
how long to wait?

Does the fan in the PSU stop when you power down?

When you think the computer is powered down (which is after the fans
stop spinning and the Power LED goes out), can you yank the power cord
from the case, plug it back in, and then power up without waiting?

Saying "old" doesn't say how old or what type of power control the
computer uses. A long time ago, like over 20 years ago, power control
was the AT style. The Power switch was a mechanical switch that
disconnected power from the PSU (which turned off, so everything lost
power). The Power switch went to the PSU. It was like wall switch to
turn off the room lights. Then came the ATX style power control. The
Power switch did not have a direct connection to the PSU. Instead the
Power switch went to the motherboard's power control logic. The Power
switch told the mobo to power down the computer, and then the mobo
told the PSU to power off. This made sure all hardware was in a
state that was prepared to lose power, not just abruptly yank away
the power.

https://en.wikipedia.org/wiki/AT_(form_factor)
https://en.wikipedia.org/wiki/ATX

ATX started back in 1995: 24 years ago. So how old is old to you?
Does the Power switch run to the PSU or to the motherboard?

Rather than attempt vague troubleshooting on vague (actually
completely undescribed) hardware, give the brand and model of:

- PSU
- Motherboard

Did you build this computer (did you or someone else fab the
computer), or is a pre-built (you buy it already built)? If a
pre-built, what is the brand and model of the computer?


I bought the computer in 2009. It was put together by somebody who is
no longer around. The motherboard is an MSI Eclipse (model MS-7520).
it is an ATX motheoboard, core i7. The power supply is a 400W made by
some off-brand Chinese company.

The one-minute waiting period starts when all the lights and the fans
are off.

--
tb
  #4  
Old November 8th 19, 11:32 PM posted to alt.comp.hardware
Paul[_28_]
external usenet poster
 
Posts: 1,467
Default Bad Power Supply

tb wrote:
On 11/8/2019 at 1:46:43 PM VanguardLH wrote:

tb wrote:

I have this desktop PC (quite old!) that when I shut it down I have
to wait at least a minute before I can reboot it. If I press the
power button before approx. one minute it does not turn on.

I'm hoping the hardware experts in this group will confirm that it
is a power supply issue, not some component on the motherboard that
is failing...

From when are you measuring the "minute" you have to wait before
pressing the Power button? Are you measuring from when you tell
Windows to shutdown, from when the shutdown screen appears, from when
the Power LED on the case goes out, or from when are you measuring
how long to wait?

Does the fan in the PSU stop when you power down?

When you think the computer is powered down (which is after the fans
stop spinning and the Power LED goes out), can you yank the power cord
from the case, plug it back in, and then power up without waiting?

Saying "old" doesn't say how old or what type of power control the
computer uses. A long time ago, like over 20 years ago, power control
was the AT style. The Power switch was a mechanical switch that
disconnected power from the PSU (which turned off, so everything lost
power). The Power switch went to the PSU. It was like wall switch to
turn off the room lights. Then came the ATX style power control. The
Power switch did not have a direct connection to the PSU. Instead the
Power switch went to the motherboard's power control logic. The Power
switch told the mobo to power down the computer, and then the mobo
told the PSU to power off. This made sure all hardware was in a
state that was prepared to lose power, not just abruptly yank away
the power.

https://en.wikipedia.org/wiki/AT_(form_factor)
https://en.wikipedia.org/wiki/ATX

ATX started back in 1995: 24 years ago. So how old is old to you?
Does the Power switch run to the PSU or to the motherboard?

Rather than attempt vague troubleshooting on vague (actually
completely undescribed) hardware, give the brand and model of:

- PSU
- Motherboard

Did you build this computer (did you or someone else fab the
computer), or is a pre-built (you buy it already built)? If a
pre-built, what is the brand and model of the computer?


I bought the computer in 2009. It was put together by somebody who is
no longer around. The motherboard is an MSI Eclipse (model MS-7520).
it is an ATX motheoboard, core i7. The power supply is a 400W made by
some off-brand Chinese company.

The one-minute waiting period starts when all the lights and the fans
are off.


Motherboards have backfeed protection and capacitors
associated with the reset sequence. A problem with
the analog electronics on the motherboard, can give
symptoms where starting doesn't work properly.

It's not always the power supply, but sometimes
involves the motherboard.

The power supply has two halves. It has the +5VSB separate
supply (supervisor). The main supply portion (3.3V/5V/12V)
can go off entirely at shutdown, but the +5VSB keeps running.

A PC power supply, cannot start, unless the +5VSB is there
to power the motherboard supervisory circuits, and the supervisory
section accepts the "front panel pulse" that starts power up.

But it won't even get that far, if the backfeed and reset
logic analog components do not "cycle" properly. Then the
starting can be upset by such analog circuits.

There was even a case, where power coming from the +5V
on the VGA cable, fed back into a computer and prevented
starting. For that user to start their PC, they would
disconnect the VGA cable, press the power button on the
PC, when they heard the beep, plug the VGA back in as
it could no longer hold the PC hostage. Pretty weird.
Don't ask me to explain how the backfeed from a VGA
cable, makes its way all the way through the video card
and into the motherboard...

We had a whole subsystem at work, power itself up via
backfeed. Just some electrical signals on 4000 series
CMOS circuits, enough current flowed backwards,
even the status LEDs on the front panel of the
subsystem lit up (weakly). The circuit nominally ran at
5V, but the power rail charged to about 3.7V and
there was enough voltage to run the status LEDs.
(4000 series CMOS is very low power, so it'll
run off a fart, in terms of power usage.)
And the subsystem was completely sane, even if
it couldn't do anything. The solution to this,
is the usage of transmission gates between
subsystems. They existed back then, but we weren't
really aware of the problem and solution at the time.
This result represented an anomaly in our test plan,
and wasn't expected to "ruin" anything.

Summary: You can test with a spare or replacement
power supply, but don't expect the symptoms
to go away. While many parts of motherboard
design follow "defacto standards", the backfeed
prevention network and components used, are
selected by the designer (custom). No two
motherboard designers do this stuff, exactly
the same way. When I've looked at the spaghetti
in the sample schematics, I just can't follow
what they're doing, because the logic spans
multiple schematic pages.

Paul
  #5  
Old December 24th 19, 11:49 AM
justincase justincase is offline
Banned
 
First recorded activity by HardwareBanter: Oct 2011
Posts: 4
Default

Quote:
Originally Posted by Paul[_28_] View Post
tb wrote:
On 11/8/2019 at 1:46:43 PM VanguardLH wrote:

tb lid wrote:

I have this desktop PC (quite old!) that when I shut it down I have
to wait at least a minute before I can reboot it. If I press the
power button before approx. one minute it does not turn on.

I'm hoping the hardware experts in this group will confirm that it
is a power supply issue, not some component on the motherboard that
is failing...

From when are you measuring the "minute" you have to wait before
pressing the Power button? Are you measuring from when you tell
Windows to shutdown, from when the shutdown screen appears, from when
the Power LED on the case goes out, or from when are you measuring
how long to wait?

Does the fan in the PSU stop when you power down?

When you think the computer is powered down (which is after the fans
stop spinning and the Power LED goes out), can you yank the power cord
from the case, plug it back in, and then power up without waiting?

Saying "old" doesn't say how old or what type of power control the
computer uses. A long time ago, like over 20 years ago, power control
was the AT style. The Power switch was a mechanical switch that
disconnected power from the PSU (which turned off, so everything lost
power). The Power switch went to the PSU. It was like wall switch to
turn off the room lights. Then came the ATX style power control. The
Power switch did not have a direct connection to the PSU. Instead the
Power switch went to the motherboard's power control logic. The Power
switch told the mobo to power down the computer, and then the mobo
told the PSU to power off. This made sure all hardware was in a
state that was prepared to lose power, not just abruptly yank away
the power.

https://en.wikipedia.org/wiki/AT_(form_factor)
https://en.wikipedia.org/wiki/ATX

ATX started back in 1995: 24 years ago. So how old is old to you?
Does the Power switch run to the PSU or to the motherboard?

Rather than attempt vague troubleshooting on vague (actually
completely undescribed) hardware, give the brand and model of:

- PSU
- Motherboard

Did you build this computer (did you or someone else fab the
computer), or is a pre-built (you buy it already built)? If a
pre-built, what is the brand and model of the computer?


I bought the computer in 2009. It was put together by somebody who is
no longer around. The motherboard is an MSI Eclipse (model MS-7520).
it is an ATX motheoboard, core i7. The power supply is a 400W made by
some off-brand Chinese company.

The one-minute waiting period starts when all the lights and the fans
are off.


Motherboards have backfeed protection and capacitors
associated with the reset sequence. A problem with
the analog electronics on the motherboard, can give
symptoms where starting doesn't work properly.

It's not always the power supply, but sometimes
involves the motherboard.

The power supply has two halves. It has the +5VSB separate
supply (supervisor). The main supply portion (3.3V/5V/12V)
can go off entirely at shutdown, but the +5VSB keeps running.

A PC power supply, cannot start, unless the +5VSB is there
to power the motherboard supervisory circuits, and the supervisory
section accepts the "front panel pulse" that starts power up.

But it won't even get that far, if the backfeed and reset
logic analog components do not "cycle" properly. Then the
starting can be upset by such analog circuits.

There was even a case, where power coming from the +5V
on the VGA cable, fed back into a computer and prevented
starting. For that user to start their PC, they would
disconnect the VGA cable, press the power button on the
PC, when they heard the beep, plug the VGA back in as
it could no longer hold the PC hostage. Pretty weird.
Don't ask me to explain how the backfeed from a VGA
cable, makes its way all the way through the video card
and into the motherboard...

We had a whole subsystem at work, power itself up via
backfeed. Just some electrical signals on 4000 series
CMOS circuits, enough current flowed backwards,
even the status LEDs on the front panel of the
subsystem lit up (weakly). The circuit nominally ran at
5V, but the power rail charged to about 3.7V and
there was enough voltage to run the status LEDs.
(4000 series CMOS is very low power, so it'll
run off a fart, in terms of power usage.)
And the subsystem was completely sane, even if
it couldn't do anything. The solution to this,
is the usage of transmission gates between
subsystems. They existed back then, but we weren't
really aware of the problem and solution at the time.
This result represented an anomaly in our test plan,
and wasn't expected to "ruin" anything.

Summary: You can test with a spare or replacement
power supply, but don't expect the symptoms
to go away. While many parts of motherboard
design follow "defacto standards", the backfeed
prevention network and components used, are
selected by the designer (custom). No two
motherboard designers do this stuff, exactly
the same way. When I've looked at the spaghetti
in the sample schematics, I just can't follow
what they're doing, because the logic spans
multiple schematic pages.

Paul
has the same problem
 




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