Question for Paul

[Astropher]

I have a Gigabye X58A-UD3R motherboard, i7-950 based system that is
showing signs of what appears to me to be a power supply fault.

If I power the system down for several hours AND switch off the AC to
the supply, when I attempt to power it back up again, pressing the
power button does nothing and then after some period of time (perhaps
20 minutes or more) the system powers up and runs normally. When it
is in the dead state, there are no LEDs illuminated on the motherboard
(except for the blue 'clear CMOS' button), the fan doesn't attempt to
spin.

I first noticed the problem a couple of months ago, and at that time
the power up delay was only a minute or so. It has progressively
reached the current state.

When the system is running, I can reboot it, power it down and
immediately power it up again with no problems. The fault only occurs
when the system has been powered down for some time (with the AC input
switched off).

The power supply is an ANTEC VP650 V2 and is just on 12 months old.
The previous power supply (a Vantec ION 520W job) died after 3 years of
service.

My question is: Do you think this is a power supply issue? The machine
runs flawlessly otherwise. if it is a power supply issue, what brand
of supply is good these days. I bought the VANTEC because it was
supposed to be a quality power supply.

 

[Paul]

I have a Gigabye X58A-UD3R motherboard, i7-950 based system that is
showing signs of what appears to me to be a power supply fault.

If I power the system down for several hours AND switch off the AC to
the supply, when I attempt to power it back up again, pressing the power
button does nothing and then after some period of time (perhaps 20
minutes or more) the system powers up and runs normally. When it is in
the dead state, there are no LEDs illuminated on the motherboard (except
for the blue 'clear CMOS' button), the fan doesn't attempt to spin.

I first noticed the problem a couple of months ago, and at that time the
power up delay was only a minute or so. It has progressively reached the
current state.

When the system is running, I can reboot it, power it down and
immediately power it up again with no problems. The fault only occurs
when the system has been powered down for some time (with the AC input
switched off).

The power supply is an ANTEC VP650 V2 and is just on 12 months old. The
previous power supply (a Vantec ION 520W job) died after 3 years of
service.

My question is: Do you think this is a power supply issue? The machine
runs flawlessly otherwise. if it is a power supply issue, what brand
of supply is good these days. I bought the VANTEC because it was
supposed to be a quality power supply.

You can test the power supply separately.

The PS_ON# wire, if you connect it to GND, the power supply should
start. You would hear the power supply fan spinning.

To do such a test, you would want to disconnect the supply from the
system, put some electrical load on it (a couple old hard drives on
the Molex cables will do). Then switch on at the back of the power
supply, then connect PS_ON# to GND. The PSU fan should spin. If
you have a multimeter, you can make a quick check of the output
voltages.

http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf

The power supply should respond instantly, each time you ground PS_ON#.
There should not be any 20 minute delay in such a test. This is to
prove the power supply is not taking a 20 minute nap.

*******

I don't know the reason for your symptoms. I've heard of these
symptoms before, but could offer no concrete suggestions for
dealing with them. The problem could be with the motherboard,
somewhere in the PS_ON# logic, maybe where a capacitor
is involved in RESET timing or the like. Some component which
isn't charging up in the expected time.

The power supply, has two supply sections. The +5VSB (the one
that is lighting your blue LED right now), has its own switching
supply. The main rails (3.3V/5V/12V) involved a bigger chunk of stuff.
The motherboard cannot "start" anything, unless +5VSB is running.
The fact a LED lights up, tells me +5VSB is present. This is why
I'm guessing this is not primarily a power supply problem. If you
had no LEDs glowing at all, I would be less certain, and then
doing a power supply test (both sections) would be necessary.

But if the +5VSB section is able to light the LED, that suggests
a motherboard problem. First the +5VSB comes on, then the motherboard
logic drives PS_ON#, then the main supply rails are turned on and
the fans spin. The motherboard is holding up the works.

These problems can be debugged to the "nearest replaceable
assembly" with a multimeter. But in terms of the logic on
the motherboard, some of the schematics, I can't even follow
what they're doing in there. The logic snakes all over the place,
and it's not always arranged in an order that points to the
organization behind it. Motherboards have things like
"backfeed cut", which disconnects power from certain
things (when the system is off), to prevent the wrong
part of the motherboard from getting charged up. It could
even be a failing backfeed, which allows +5VSB to get into
a part of the circuit where normally +5V runs. When that
happens, the motherboard "can't tell it is turned off". So
the logic state is inconsistent. There is no reason
to generate a power-on sequence, if you think you're
already on.

On one system, the back feeding path turned out to be the
computer monitor. If the computer monitor was disconnected,
pushing the front power button would bring up the computer instantly.
Then, the user could plug in their VGA connector again
and start work. The VGA cable at one time had a +5V pin,
and some monitors delivered power to that pin. And it had
something to do with something power related, flowing back
towards the motherboard. Now, if that was my system,
I'd have made a VGA to VGA extension cable, and removed
the +5V pin at one end. I think a lot of modern VGA
cables are missing that pin (so making such a cable
is no longer necessary), so this really shouldn't
be possible any more. But again, I mention this, so if
you're using VGA, you can unplug the monitor and see
if the system starts (cold) faster than 20 minutes time.

Paul

 

[VanguardLH]

I have a Gigabye X58A-UD3R motherboard, i7-950 based system that is
showing signs of what appears to me to be a power supply fault.

If I power the system down for several hours AND switch off the AC to
the supply, when I attempt to power it back up again, pressing the
power button does nothing and then after some period of time (perhaps
20 minutes or more) the system powers up and runs normally. When it
is in the dead state, there are no LEDs illuminated on the motherboard
(except for the blue 'clear CMOS' button), the fan doesn't attempt to
spin.

I first noticed the problem a couple of months ago, and at that time
the power up delay was only a minute or so. It has progressively
reached the current state.

When the system is running, I can reboot it, power it down and
immediately power it up again with no problems. The fault only occurs
when the system has been powered down for some time (with the AC input
switched off).

The power supply is an ANTEC VP650 V2 and is just on 12 months old.
The previous power supply (a Vantec ION 520W job) died after 3 years of
service.

My question is: Do you think this is a power supply issue? The machine
runs flawlessly otherwise. if it is a power supply issue, what brand
of supply is good these days. I bought the VANTEC because it was
supposed to be a quality power supply.

Seems a CMOS battery replacement is a cheap diagnosis step.

 

[Paul]

Seems a CMOS battery replacement is a cheap diagnosis step.

It's a possibility. But not all motherboards are stopped
cold by a completely flat CMOS battery. Only some designs
seem to be susceptible. I have systems here, with flat
batteries (my in-storage collection), that still start.

The scenario for this would be:

1) Battery gets loaded by the unplugged interval the
machine experiences when not in usage.

2) When the power comes back, +5VSB through the 3VSB rail,
charges the battery through the ORing diode (reverse
leakage current of less than 1 microamp). The battery
is not supposed to charge through the diodes, and the
diodes are there to prevent charging. The diode spec
should be less than 1 microamp leakage at max temperature,
in this application (the max current allowed to flow into a
CR2032 non-rechargeable battery).

3) Once battery terminal isn't exactly at 0.0V any more,
system starts. This only applies to machines where the
thing is killed by a completely flat battery. And I don't
see a pattern as to which systems are vulnerable and which
aren't.

This flat battery thing could be a feature of the SuperI/O, but
I've not see a comment about such a response in a SuperI/O datasheet,
and I have a collection of around a half-dozen of those.

Paul

 

[VanguardLH]

It's a possibility. But not all motherboards are stopped
cold by a completely flat CMOS battery. Only some designs
seem to be susceptible. I have systems here, with flat
batteries (my in-storage collection), that still start.

The scenario for this would be:

1) Battery gets loaded by the unplugged interval the
machine experiences when not in usage.

2) When the power comes back, +5VSB through the 3VSB rail,
charges the battery through the ORing diode (reverse
leakage current of less than 1 microamp). The battery
is not supposed to charge through the diodes, and the
diodes are there to prevent charging. The diode spec
should be less than 1 microamp leakage at max temperature,
in this application (the max current allowed to flow into a
CR2032 non-rechargeable battery).

3) Once battery terminal isn't exactly at 0.0V any more,
system starts. This only applies to machines where the
thing is killed by a completely flat battery. And I don't
see a pattern as to which systems are vulnerable and which
aren't.

This flat battery thing could be a feature of the SuperI/O, but
I've not see a comment about such a response in a SuperI/O datasheet,
and I have a collection of around a half-dozen of those.

Paul

It was the OP saying the computer wouldn't power up for awhile by BOTH
powering down (presumably using the Power switch) AND switching off the
A/C to the supply (by a switch on the back of the PSU or a power strip
into which the PSU was connected).

When an ATX computer is powered down using the Power switch, the PSU
still provides +5VSB to the motherboard. This is used to also provide
the +3V to the RTC chip to keep it alive while the computer is "powered
down" (but the PSU is still alive by providing +5VSB if the A/C to the
PSU is still live). There'll be no +5VSB hence no +3V to RTC is the A/C
power is disconnected from the PSU.

With a dead battery, the defaults from the EEPROM copy of the BIOS
settings has to get copied into the CMOS RAM inside the RTC. I'm not
sure this qualifies as a true reset of the CMOS table to ensure all BIOS
defaults gets copied into CMOS. As I recall but from old RTC designs,
there was a capacitor used to maintain the +3V needed to retain the
settings in the CMOS RAM. This was to allow the user time to remove a
CMOS battery while the PSU had no A/C to put in a replacement coin cell
battery without the CMOS getting [partially] cleared.

The user said it took a long time after disconnecting the A/C source
before the problem cropped up. Well, I've had old systems that only
gave me 18 minutes and up to 22 hours after removing the CMOS battery
before the CMOS was unable to retain [some of] the settings. With a
reset after putting in a new CMOS battery, I would consider the state of
the CMOS table to be corrupt so who knows what effect it may have.

So I figure for the cost of a CR2023 coin cell battery, remove the old
battery, put in the new battery, and short the CMOS reset jumper on the
mobo that this could be eliminated as the source of the problem. If the
user had customized the CMOS copy of the BIOS settings or selected a
different settings scheme (e.g., optimal, overclocked, etc) then he
would have to reconfigure those settings after resetting the CMOS table
or, at least, in the BIOS settings have it force a copy of BIOS settings
into CMOS.

 

[Paul]

It's a possibility. But not all motherboards are stopped
cold by a completely flat CMOS battery. Only some designs
seem to be susceptible. I have systems here, with flat
batteries (my in-storage collection), that still start.

The scenario for this would be:

1) Battery gets loaded by the unplugged interval the
machine experiences when not in usage.

2) When the power comes back, +5VSB through the 3VSB rail,
charges the battery through the ORing diode (reverse
leakage current of less than 1 microamp). The battery
is not supposed to charge through the diodes, and the
diodes are there to prevent charging. The diode spec
should be less than 1 microamp leakage at max temperature,
in this application (the max current allowed to flow into a
CR2032 non-rechargeable battery).

3) Once battery terminal isn't exactly at 0.0V any more,
system starts. This only applies to machines where the
thing is killed by a completely flat battery. And I don't
see a pattern as to which systems are vulnerable and which
aren't.

This flat battery thing could be a feature of the SuperI/O, but
I've not see a comment about such a response in a SuperI/O datasheet,
and I have a collection of around a half-dozen of those.

Paul

It was the OP saying the computer wouldn't power up for awhile by BOTH
powering down (presumably using the Power switch) AND switching off the
A/C to the supply (by a switch on the back of the PSU or a power strip
into which the PSU was connected).

When an ATX computer is powered down using the Power switch, the PSU
still provides +5VSB to the motherboard. This is used to also provide
the +3V to the RTC chip to keep it alive while the computer is "powered
down" (but the PSU is still alive by providing +5VSB if the A/C to the
PSU is still live). There'll be no +5VSB hence no +3V to RTC is the A/C
power is disconnected from the PSU.

With a dead battery, the defaults from the EEPROM copy of the BIOS
settings has to get copied into the CMOS RAM inside the RTC. I'm not
sure this qualifies as a true reset of the CMOS table to ensure all BIOS
defaults gets copied into CMOS. As I recall but from old RTC designs,
there was a capacitor used to maintain the +3V needed to retain the
settings in the CMOS RAM. This was to allow the user time to remove a
CMOS battery while the PSU had no A/C to put in a replacement coin cell
battery without the CMOS getting [partially] cleared.

The user said it took a long time after disconnecting the A/C source
before the problem cropped up. Well, I've had old systems that only
gave me 18 minutes and up to 22 hours after removing the CMOS battery
before the CMOS was unable to retain [some of] the settings. With a
reset after putting in a new CMOS battery, I would consider the state of
the CMOS table to be corrupt so who knows what effect it may have.

So I figure for the cost of a CR2023 coin cell battery, remove the old
battery, put in the new battery, and short the CMOS reset jumper on the
mobo that this could be eliminated as the source of the problem. If the
user had customized the CMOS copy of the BIOS settings or selected a
different settings scheme (e.g., optimal, overclocked, etc) then he
would have to reconfigure those settings after resetting the CMOS table
or, at least, in the BIOS settings have it force a copy of BIOS settings
into CMOS.

You only replace the CR2032 with the power off. So there is no
power on the system at that point. You could use the CLR_RTC jumper
to drain any remaining current. (The reason for unplugging, is the battery
casing is a conductor all over, and it tends to hop out of the socket while
you're working on it, and it could get into all sorts of mischief if it
shorts the wrong terminals together. Better to just power everything
off before beginning a battery swap.)

The capacitor just after the ORing diode, where it meets the
three volt input on the Southbridge, that capacitor is there
for noise reasons. It's a bypass capacitor. On the two reference
schematics from Intel pictured here, one uses a 0.1uF and the
other uses a 1.0uF. Those aren't exactly large capacitors.
Motherboard makers use 100uF for USB power hold-up (inrush
buffering), so there are larger caps they could use
if they wanted. There isn't a conscious effort here to
hold up the battery terminal while the battery is out
of the socket. It really depends on how fast you are at
changing the battery, and that battery flops around like a fish
when you're working on one of those.

http://i61.tinypic.com/2vsnfqs.gif

The CMOS is protected by a crude checksum, and
the BIOS will re-initialize the CMOS if the checksum
is wrong. But it's not a particularly strong scheme.

And I don't know if there are any "CMOS well" register bits,
that record that the chip has come up from a dead state.
That would be a better way to do automated reinitialization.

The BIOS exit menu has a "restore defaults" option,
if you want to use it upon entering the BIOS. That's
a quick way to request the CMOS memory bits be reloaded.

The OP has been turning his PC off at the back. And that
gives an opportunity for a battery on its last legs
to be wobbling around the point at which the motherboard
might not be able to start. The evidence to date, is
motherboards that don't start, the battery seems to be
at 0.0V (completely flat). If there is any sort of
voltage left on it, the board still starts. It only
takes three weeks of discharging the battery by the CMOS,
to "walk down" the knee of the battery discharge curve and
hit 0.0V. So if your theory is correct, the delay at
startup a month from now, will change from 20 minutes to
infinity Because then the battery will be really flat.

One other thing to note about that picture above. There
is no monitoring connection that comes straight from the
battery. I have a suspicion that some designs (not Intel),
they pick up a connection right from the battery and run
it over to the SuperIO. And that might be the difference
between designs that don't start, and ones that do.

Paul

 

[Astropher]

You can test the power supply separately.

The PS_ON# wire, if you connect it to GND, the power supply should
start. You would hear the power supply fan spinning.

To do such a test, you would want to disconnect the supply from the
system, put some electrical load on it (a couple old hard drives on
the Molex cables will do). Then switch on at the back of the power
supply, then connect PS_ON# to GND. The PSU fan should spin. If
you have a multimeter, you can make a quick check of the output
voltages.

http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf

The power supply should respond instantly, each time you ground PS_ON#.
There should not be any 20 minute delay in such a test. This is to
prove the power supply is not taking a 20 minute nap.

Thanks very much for the suggestions Paul. I will try yours and
Vanguard's suggestions the next time I power the machine down fully.

I normally run the machine 24/7 except for when I plan to leave the
premises for longer than an hour during the storm season (which is
now). We get vicious electrical storms here in the sub-tropical and
tropical areas of Eastern Australia during the summer and they dvelop
rapidly.

 

[Flasherly]

If I power the system down for several hours AND switch off the AC to
the supply, when I attempt to power it back up again, pressing the
power button does nothing and then after some period of time (perhaps
20 minutes or more) the system powers up and runs normally. When it
is in the dead state, there are no LEDs illuminated on the motherboard
(except for the blue 'clear CMOS' button), the fan doesn't attempt to
spin.

Can also pull the plug completely from the wall, plug it back in, turn
back ON the power-supply's toggle. Don't allow, of course, provide it
with the requisite 20min.

Then hold down [IN] the case's PWR ON for 10 to 15 seconds, (for
effecting an continuous open condition on the PWR ON MB jumper
blocks).

See if it comes up then. I've run into something similar with PS
logic (both ways turning off, or on, when holding in switch/logic
exhibits that "extended" effect).

Might look to see if your BIOS setting for PWR ON/Resume upon
restoration of POWER (due to brown/blackouts) will function. Both
ways, to include disabling it.

 

[Flasherly]

effecting an continuous open condition

'scuse. That should be closed/shorted contacts

 

[Astropher]

Seems a CMOS battery replacement is a cheap diagnosis step.

It appears that it was the CMOS battery. I replaced the battery a
couple of days ago, and today the machine was powered down with the AC
disconnected for 12 hours. It started up again properly without delay.

Thanks.

 

[Paul]

It appears that it was the CMOS battery. I replaced the battery a
couple of days ago, and today the machine was powered down with the AC
disconnected for 12 hours. It started up again properly without delay.

Thanks.

Weird. And thanks for posting back. +1 for VanguardLH.
And another item for the "big book of busted hardware"
Where we learn by remote observations.

Paul

 

[Astropher]

Weird. And thanks for posting back. +1 for VanguardLH.
And another item for the "big book of busted hardware"
Where we learn by remote observations.

It is pretty selfish not to follow through by posting back results.

By strange coincidence, this week a friend emailed about how his
computer was taking a long time to power up. It exhibited pretty much
the same symptoms as mine. I know he has a relatively new power supply
and It is also a Gigabyte motherboard. I will post the resuts when he
eventually gets around to replacing his battery.