motherboard 5v

My legacy ECS K7S5A motherboard BIOS hardware monitor says the 5v is
low. So I used a multimeter to check a USB 5v header pin, and it says
4.75v.

The power supply 5v disk connector has exactly 5v, so the power supply
is good.

If I replace the 5v AGP card with a 3.3v card, the USB pin measures
4.85v. So the 5v video card causes a 0.1v drop on the motherboard 5v.

Is 4.75v PCI/USB safe? Should I replace the AGP video card to get the
extra 0.1v? I hear that 5% tolerance is OK, but 4.75v is right at the
edge of 5%.

The motherboard seems to work OK, but I wonder if it's safe.

On Mon, 03 Jun 2019 15:21:08 +0000, T. Ment wrote:

My legacy ECS K7S5A motherboard BIOS hardware monitor says the 5v is
low. So I used a multimeter to check a USB 5v header pin, and it says
4.75v.

The power supply 5v disk connector has exactly 5v, so the power supply
is good.

If I replace the 5v AGP card with a 3.3v card, the USB pin measures
4.85v. So the 5v video card causes a 0.1v drop on the motherboard 5v.

Is 4.75v PCI/USB safe? Should I replace the AGP video card to get the
extra 0.1v? I hear that 5% tolerance is OK, but 4.75v is right at the
edge of 5%.

The motherboard seems to work OK, but I wonder if it's safe.

Replace the power supply. The 5v disk connector may well come from
another regulator. At the very least measure the 5v at the motherboard
multiconector from the psu.

--
Regards - Rodney Pont
The from address exists but is mostly dumped,
please send any emails to the address below
e-mail rpont (at) gmail (dot) com

On Mon, 03 Jun 2019 17:00:42 +0100 (BST), rp wrote:

Replace the power supply.

It's a $20 special. I don't care about perfection.


The 5v disk connector may well come from another regulator. At
the very least measure the 5v at the motherboard multiconector
from the psu.

I won't buy another power supply if this one gets me by. My question is,
what tolerance is safe.

T. Ment wrote:
On Mon, 03 Jun 2019 17:00:42 +0100 (BST), rp wrote:

Replace the power supply.

It's a $20 special. I don't care about perfection.


The 5v disk connector may well come from another regulator. At
the very least measure the 5v at the motherboard multiconector
from the psu.

I won't buy another power supply if this one gets me by. My question is,
what tolerance is safe.

You can compare to a picture here.

This is just the first picture I could find, bigger than a thumbnail.

https://www.badcaps.net/forum/showthread.php?t=2265

The board doesn't have an ATX12V 2x2 power connector, with
the two yellow wires and two black wires.

That means the *CPU* runs off +5V, as well as lots of
other logic. It's natural for such an unbalanced load
situation (only an amp or two load on +12V, but
15 amps off the +5V), for the +5V to be a little
on the low side.

This is called "cross-regulation". There is only one
feedback loop in the ATX power supply for regulation.
What you'd find is, the +5V resting at its low limit,
and the +12V "higher than normal". If an ATX supply is
"non-compliant to crossloading", then the +5V could
even be too low and out-of-spec.

These are examples of ATX specs, of various generations.
The 1.1 version was back when power supplies still had a
-5V rail. The pin on the main connector is missing on
modern supplies, where the =5V pin used to be located.

# This is 20 pin, back when -5V was still on the connector.
http://web.archive.org/web/200304240...12V_PS_1_1.pdf

Table 3. DC Output Voltage Regulation
Output Range Min. Nom. Max. Unit
+12VDC (1) ±5% +11.40 +12.00 +12.60 Volts
+5VDC ±5% +4.75 +5.00 +5.25 Volts
+3.3VDC ±5% +3.14 +3.30 +3.47 Volts
-5VDC ±10% -4.50 -5.00 -5.50 Volts === pre-year-2000 PSUs
-12VDC ±10% -10.80 -12.00 -13.20 Volts
+5VSB ±5% +4.75 +5.00 +5.25 Volts

# This is 20 pin, with the -5V pin pulled from the connector.
https://web.archive.org/web/20040731...X12V_1_3dg.pdf

Table 2
Output Range Min. Nom. Max. Unit
+12VDC (1) ±5% +11.40 +12.00 +12.60 Volts
+5VDC ±5% +4.75 +5.00 +5.25 Volts
+3.3VDC (2) ±5% +3.14 +3.30 +3.47 Volts
-12VDC ±10% -10.80 -12.00 -13.20 Volts === Used for serial port RS232 chip, dont care
+5VSB ±5% +4.75 +5.00 +5.25 Volts

# This covers 24 pin versions of ATX PSU
https://web.archive.org/web/20070103...public_br2.pdf

Table 2

Output Range Min. Nom. Max. Unit
+12V1DC (1) ±5% +11.40 +12.00 +12.60 Volts \___ Allows ATX12V 2x2 to come from its own src
+12V2DC (3) ±5% +11.40 +12.00 +12.60 Volts / even though cct might only have one xfmr
+5VDC ±5% +4.75 +5.00 +5.25 Volts
+3.3VDC (2) ±5% +3.14 +3.30 +3.47 Volts
-12VDC ±10% -10.80 -12.00 -13.20 Volts
+5VSB ±5% +4.75 +5.00 +5.25 Volts

The 3.3V rail has a "private" remote sense wire bonded to
its pin. You will see two wires going into one of the
3.3V pins, and this allows "sniffing" the 3.3V right
at the load. The +5V rail doesn't have this (there were
a few supplies with separate regulation, but that's not
something you will see on a $20 supply).

In any case, the most likely thing to happen to a "+5V mobo",
is some discoloration where the pins are overheating on the
main connector. While there are four wires to carry +5V, you'll
typically find, by using a clamp-on ammeter, that two pins
carry 0.5A more than they should, and two pins carry 0.5A
less than they should. This is called "current hogging" and
it takes careful layout work to balance the pins better.

Back when they made *dual* socket Athlon motherboards,
some of those used to burn on the main connector, due to
a lack of ampacity. You're drawing 30A of current through
24A worth of pins, something like that. Back in the old
days, you could actually get some supplies with 40A
on the +5V, even if the wire couldn't really handle it.

If your device is stable, I wouldn't worry about it
too much. After all, it's run this long, and the caps
didn't burst on it, so you're in "bonus time" country
on your purchase.

*******

Modern power supplies have most of their amps on +12V.
A modern supply is one with an "80%+" efficiency rating
and active power factor correction (PFC).

Typically the +5V is only 20A, and the combined
3.3V and 5V output may not be sufficient to run
a "good" AGP video card plus your processor at the
same time. Some supplies have, say, 3.3V @ 20A, 5V @ 20A,
combined watts on the two rails less than 130W. And
your board is getting close to the limit.

Even if you bought a "1200W PSU", it could tip over, because
they still use a puny 3.3V/5V secondary converter board
for the low rails. And *all* your load is on the low rails.

I used to draw 25A on my Nforce2 board when gaming,
and the supply was good for that much. I could
measure that with my clamp-on ammeter. Eventually, the
end-connector on the video card burned off, and I had
to solder the +5V back on. Worked a treat after being
soldered in place (no more ohmic connections). These
things happen, when a connector works loose.

*******

You're doing just fine. Relax and enjoy your machine,
until that Athlon cooks out and smokes. They discolor
after a while, even if you take care of them.

Paul

On Mon, 03 Jun 2019 14:48:43 -0400, Paul wrote:

https://www.badcaps.net/forum/showthread.php?t=2265

The board doesn't have an ATX12V 2x2 power connector, with
the two yellow wires and two black wires.

That means the *CPU* runs off +5V, as well as lots of
other logic. It's natural for such an unbalanced load
situation (only an amp or two load on +12V, but
15 amps off the +5V), for the +5V to be a little
on the low side.

This is called "cross-regulation". There is only one
feedback loop in the ATX power supply for regulation.
What you'd find is, the +5V resting at its low limit,
and the +12V "higher than normal". If an ATX supply is
"non-compliant to crossloading", then the +5V could
even be too low and out-of-spec.

These are examples of ATX specs, of various generations.
The 1.1 version was back when power supplies still had a
-5V rail. The pin on the main connector is missing on
modern supplies, where the =5V pin used to be located.


Mine has -5v, a 20/24 main connector, a 4 pin +12v, and 34a on the +5v.
With a loud pop, it blew a capacitor the first time I powered it on, but
after replacing the failed cap, it works. It was a smaller cap, not one
of the two big ones. They scare me. I would throw it out if they blew.


+5VDC ±5% +4.75 +5.00 +5.25 Volts

I see 4.75v on a USB header pin. It's within spec, just barely.


You're doing just fine. Relax and enjoy your machine,
until that Athlon cooks out and smokes.

I have an Athlon that went into thermal runaway once. Don't know what
caused it. The machine froze, and the CPU heatsink burned my finger when
I touched it, like a hot burner on a stove.

After cooling down, it's run fine ever since. I never leave it running
when I'm gone though. I'm afraid it could happen again, catch fire, and
burn the house down.

On Mon, 03 Jun 2019 14:48:43 -0400, Paul wrote:

This is just the first picture I could find, bigger than a thumbnail.

https://www.badcaps.net/forum/showthread.php?t=2265

The board doesn't have an ATX12V 2x2 power connector, with
the two yellow wires and two black wires.

I wondered if the power supply would do any better on a motherboard with
a 12V connector.


That means the *CPU* runs off +5V, as well as lots of
other logic. It's natural for such an unbalanced load
situation (only an amp or two load on +12V, but
15 amps off the +5V), for the +5V to be a little
on the low side.

This is called "cross-regulation". There is only one
feedback loop in the ATX power supply for regulation.
What you'd find is, the +5V resting at its low limit,
and the +12V "higher than normal". If an ATX supply is
"non-compliant to crossloading", then the +5V could
even be too low and out-of-spec.

So I swapped the K7S5A for a motherboard which has the 12v connector.
Now my multimeter reads 5.16v on the USB header pins. That's more like
it. To make sure, I swapped again for a third motherboard (12v). Same
result, 5.16v.

My $20 power supply is OK with a 12v motherboard. I'll match the K7S5A
with a better power supply.

T. Ment wrote:


So I swapped the K7S5A for a motherboard which has the 12v connector.
Now my multimeter reads 5.16v on the USB header pins. That's more like
it. To make sure, I swapped again for a third motherboard (12v). Same
result, 5.16v.

My $20 power supply is OK with a 12v motherboard. I'll match the K7S5A
with a better power supply.

And that's the cross-loading effect.

Balancing the loads leads to closer-to-correct
regulation.

If one rail of a three-rail supply is heavily loaded,
the fact there is only one feedback loop means
two rails will be high and one rail will be low.

Only a few supplies used separate circuits for
the rails. The concept never caught on. I think
the regulation on those could be in the 2% or so
ballpark.

There have also been a few supplies with four separate
12V rails. CPU1 and CPU2, motherboard, PCIe, some sort
of split like that. You had to make sure on those, that
the rails that were independent, didn't get joined
by accident. (That's because they're only nominally
12V, and if they are slightly different potentials,
a large current can flow between them. And also,
the ATX design is not push-pull, it's only push, and if
a "rail goes high", nothing actively works to bring
that voltage down.)

On the motherboard, there is only one push-pull
regulator, and that's the Vtt regulator for terminating
DIMM buses. Plus or minus two amps flows from that
one. It either has to sink 2 amps or source 2 amps,
on a nanosecond level basis.

You've done a good job by selecting a 12V Athlon board.
When I told people I had a board that ran the CPU
off 5V, not a lot of people believed it.

There are some other goofy practices. Biostar, on a
number of motherboards, joined ATX12V 2x2 12V to
the motherboard yellow 12V wire. One is 12V1 and the other
is 12V2. Now, because a lot of ATX supplies power
12V1 and 12V2 come from the same transformer, there is
no potential difference. It's only when you use
a supply with entirely separate 12V1 and 12V2, that
this would be a bad idea. I never did see an explanation
from Biostar, as to why this was a good idea.

I think the evidence for this came, when a Biostar owner
of a P4 board, accidentally forgot to plug in ATX12V
2x2, and the CPU and motherboard booted and ran without
it. That's the evidence they're joined on the motherboard.
I can't think of any other brands that do this.

If you need help on connectors, this site has a page on
ATX supplies.

http://www.playtool.com/pages/psucon...onnectors.html

Paul

T. Ment wrote:

On Mon, 03 Jun 2019 17:00:42 +0100 (BST), rp wrote:

Replace the power supply.

It's a $20 special. I don't care about perfection.

That is way too cheap for a decent power supply. When I do a build,
most of the PSUs that I end up looking at are $80 at a minimum but
usually spend a lot more. However, I don't know what you got for
capacity (VA or watts) for your PSU, or its efficiency (less efficient =
more heat = more thermal stress = less capacity to internal components
since the A/C outlet isn't changing its voltage).

Figure on losing 5% capacity each year with a decent PSU. That's why I
buy PSUs that are much higher in capacity than the load they will
initially need to handle. For a 400W load, I'd get a 750W PSU because
in 8 years (what I like to build for longevity) the PSU will still be
more than enough at 66% of its initial capacity. The 5% is a rough
estimate of capacity reduction, but PSUs do wane over time. Cheapies
die off much quicker. The PSU supplies the life blood to the computer.
If you do the build, you are the hematologist for the computer.

How old is your $20 PSU?

Was it a pre-built computer or did you do your own build? The PSUs that
come in pre-builts are often minimal for the standard configuration by
the model (with the same PSU used within a family of models). They
don't overbuild since they're maximizing their profit margin.

The 5v disk connector may well come from another regulator. At
the very least measure the 5v at the motherboard multiconector
from the psu.

I won't buy another power supply if this one gets me by. My question is,
what tolerance is safe.

4.75V is the minimum. Less voltage means supplying more current to
handle the same load, and more current puts more thermal stress on the
supply components. The computer's PSU is a switching power supply.
Unless you have an oscilloscope, you only know the average voltage, but
won't know how much ripple there is.

https://www.tomshardware.com/reviews...u,4042.html#p3

Also, rare few consumers every calibrate their multimeters. They buy
them and figure they are accurate, and think they will remain accurate.
Calibration costs money and why consumers rarely get their meters
calibrate initially or at 5-year intervals. Consumers get their meters
calibrated less than 1% as often as they check their car's tire
pressures, so consumers never get their meters calibrated. Considering
the low-end meters that consumers buy, calibration is usually more
expensive (perhaps $95) than the meter. As such, consumer-grade
non-calibrated meters are only to give an indication of voltage level,
not a precise measurement. Although you measured 4.75V, was it really
that voltage? The voltage could be worse (lower) or better (higher).

Have you noticed any of your USB devices not functioning or acting
flaky? Some USB devices don't need power from the USB port since they
have their own, like for printers, a UPS (with its USB connection for
monitoring software), and some external HDDs in cases with their own
power adapter. It would be the non-self-powered USB devices you'd have
problems with.

Computers always cost money - to buy, to maintain, to upgrade, for
Internet access, the power consumption, etc - so save up and get a
better PSU. $20 is a throw-away PSU. Presumably that wasn't an 80% off
special sale.

On Mon, 3 Jun 2019 14:28:39 -0500, VanguardLH wrote:

It's a $20 special.

That is way too cheap for a decent power supply. When I do a build,
most of the PSUs that I end up looking at are $80 at a minimum but
usually spend a lot more.

I don't need an economics expert. I only asked about voltage.

T. Ment wrote:

On Mon, 3 Jun 2019 14:28:39 -0500, VanguardLH wrote:

It's a $20 special.

That is way too cheap for a decent power supply. When I do a build,
most of the PSUs that I end up looking at are $80 at a minimum but
usually spend a lot more.

I don't need an economics expert. I only asked about voltage.

Oh, so quality of the PSU, it voltage regulation, ripple, accuracy of
your multimeter, reduction in capacity as the PSU ages, less voltage
means more current for same power load all have nothing to do with
"about voltage". Voltage isn't the only factor in powering the
USB-attached devices (which could be low- or high-power devices but you
didn't identify them).

Good luck with the other respondents. According to your reply here,
even Paul went off-topic discussing bad caps, cross-regulation,
efficiency, and other topics. Maybe some other respondents might show
up later that narrowing address just "is 4.75V enough" but with a total
lack of describing the USB devices.

Bye bye.