On 6/26/2021 11:04 AM, JAB wrote:
> My Win7 desktop fizzled yesterday....power supply is good...tested on
> another desktop computer.
>
> When booting up, is the CPU required to activate power supply?
>
> Either motherboard or CPU...
>
>
> I'm using a 2017 model year ASUS laptop... X550LN... with Win_8.1

I would agree, either motherboard or CPU... cross posted to
alt.windows7.general and alt.comp.microsoft.windows

On Sat, 26 Jun 2021 16:07:56 -0400, Michael Trew <mt999999@ymail.com>
wrote:

> either motherboard or CPU

I went ahead and bought a CPU and Motherboard via Ebay...

I'll insert CPU first......no go...install "new" motherboard

When power supply boots up, it must "see" all powered circuits
(memory, devices, CPU, etc) are good.

I was using a 100W CPU, AMD A8-3850, but via Ebay got a 65W one, AMD
A8-3820.

I've replaced motherboard and CPU once before....

Installed video card may be using more current since I upped it to max
resolution ability, UXGA, when I got the new monitor. I removed card,
but computer would not boot. From time to time, when playing Youtube
vids, audio/video would blank out for a moment when enlarging screen
size...so no sound and video for a moment...I don't know what was
causing this "reset," but CPU would have been involved.

I don't want to buy another computer currently, but had considered
buying one around December.

JAB wrote:
> On Sat, 26 Jun 2021 16:07:56 -0400, Michael Trew <mt999999@ymail.com>
> wrote:
>
>> either motherboard or CPU
>
> I went ahead and bought a CPU and Motherboard via Ebay...
>
> I'll insert CPU first......no go...install "new" motherboard
>
> When power supply boots up, it must "see" all powered circuits
> (memory, devices, CPU, etc) are good.
>
> I was using a 100W CPU, AMD A8-3850, but via Ebay got a 65W one, AMD
> A8-3820.
>
> I've replaced motherboard and CPU once before....
>
> Installed video card may be using more current since I upped it to max
> resolution ability, UXGA, when I got the new monitor. I removed card,
> but computer would not boot. From time to time, when playing Youtube
> vids, audio/video would blank out for a moment when enlarging screen
> size...so no sound and video for a moment...I don't know what was
> causing this "reset," but CPU would have been involved.
>
> I don't want to buy another computer currently, but had considered
> buying one around December.

A power supply does not boot up.

It's subservient. It does your bidding.

Here are three specs. The last one, version 2.2, is relevant
to most users today.

# This is 20 pin, back when -5V was still on the connector (pin 18 present).
http://web.archive.org/web/20030424061333/http://www.formfactors.org/developer/specs/atx/ATX_ATX12V_PS_1_1.pdf

# This is 20 pin, with the -5V pin pulled from the connector (pin 18 missing)
https://web.archive.org/web/20040731003917if_/http://www.formfactors.org:80/developer/specs/ATX12V_1_3dg.pdf

# This covers 24 pin versions of ATX PSU (pin 20 missing)
https://web.archive.org/web/20070103034205if_/http://www.formfactors.org:80/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf

For the last link there, look at page 25.

Assume the PSU is plugged in, the 0/1 switch on the back
is in the "1" position and the PSU is on.

The motherboard sends PS_ON#. A zero volt signal means
"Turn on please and spin that fan".

The power supply charges the rails. For around 35 milliseconds
or so, the power supply overcurrent detection is disabled,
while the power supply charges up all the capacitors. If an
overcurrent condition exists after 35 milliseconds, the PSU
stops. This is the sequence that causes the "PSU fan to jiggle".

When the main supplies are almost fully up to the final
value, the PSU has an output logic signal, shown as
PWR_OK in the diagram, and active high. Probably a +5V
value, indicating "we are ready to go here".

It is at this point, that the motherboard can
check a few things on its end, and start POST.
The motherboard has power converters on board as well,
and the "PWR_OK" from those must be gated with the
PSU signal, before the motherboard will jump to the
RESET vector and firmware execution starts. So sometimes,
the PSU signal, you check with a multimeter, it's OK,
but the motherboard, some internal converter isn't
finishing up properly, and the motherboard won't POST.

You can buy "Port 80 POST cards" with two or four
seven segment LED displays onboard. Some enthusiast
motherboards have the seven segment displays, right
on the motherboard, for debug. When POST starts,
numeric values flash on the LEDs, indicating "progress"
and not "error codes". This allows a person to check
what phase of POST is starting or whatever. If the display
stays at 0x00 or 0xFF, then the CPU never executed anything.

So that's a very brief introduction to startup.

At least sometimes, the motherboard is unable to make
a good signal level on PS_ON# and this prevents takeoff.
It's unclear why the frequency of occurrence of this fault
is so high, but it comes up time and again. The symptoms
in that case would be, you press the button on the front...
and nothing happens. In such cases, you examine carefully
the fan on the PSU. If you press the button and the PSU
fan "jiggles a bit", that's overload on the PSU. If
the PSU fan stays stock still, when you press the button,
that could be PS_ON# is not good quality. The PSU could be
flattening it (shorting it out), or the motherboard pad driver
for PS_ON# is weak.

As a consequence, a multimeter probe shoved into the back
of the 24 pin main power connector, allows checking logic
levels on PS_ON#, then PWR_OK, to see what the PSU is being
told, and... whether it is obeying or not.

My first PSU, it became "weak". The 12V output would rise to
12V OK, but the PSU was so weak, it could only run two fans
and no computer. If you connected the computer to it, it
would never have PWR_OK asserted, because the 12V would be
flattened by the normal machine load. That's another example
of a fault type.

When the POST display finally goes blank, that's when
the BIOS POST hands off to the OS, and OS boot finally starts.

And the manual never has all the POST codes in it, and
the stupid BIOS always freeze on a POST code that is
not in the manual :-) Such is life.

Paul

On Sat, 26 Jun 2021 20:31:15 -0400, Paul <nospam@needed.invalid>
wrote:

>You can buy "Port 80 POST cards" with two or four
>seven segment LED displays onboard.

Thanks for the tidbits....ain't no beeps on that computer...it's
dead...no response.

"For motherboards that do not have a port 80 display listening to the
beep code helps identify the error."

<https://www.computerhope.com/jargon/p/port80.htm>

On Sat, 26 Jun 2021 20:31:15 -0400, Paul <nospam@needed.invalid>
wrote:

>So that's a very brief introduction to startup.

Tidbit - " [ Note: All these voltages will vary slightly for each
combination of power supply, motherboard, disk drive(s) and various
peripherals (since the number of electronic components drawing current
alters a power supply's load), but its output voltages should never
fluctuate upon reaching normal operating levels.

If any of its outputs has an unacceptable amount of noise (or AC
ripple[1]), then one or more of the motherboard's components, such as
its Memory, may fail the Power-On Self Test, keeping the PC's
operating system from ever booting up. ....]"

<https://thestarman.pcministry.com/PCboot.htm>

JAB wrote:
> On Sat, 26 Jun 2021 20:31:15 -0400, Paul <nospam@needed.invalid>
> wrote:
>
>> You can buy "Port 80 POST cards" with two or four
>> seven segment LED displays onboard.
>
> Thanks for the tidbits....ain't no beeps on that computer...it's
> dead...no response.
>
>
> "For motherboards that do not have a port 80 display listening to the
> beep code helps identify the error."
>
> <https://www.computerhope.com/jargon/p/port80.htm>
>

You can start by checking for +5VSB.

The front panel switch goes through a latch and timer circuit,
before driving out as PS_ON# to the PSU.

That intervening logic is powered by +5VSB.

If +5VSB is shorted out (user attempts to charge too
many iPhones), then the intervening logic has no power,
and with no power, it cannot actuate the control for PS_ON#.

+5VSB
/ | (PS_ON#)
GND ---X X---- latch ------------ PSU ----- +3.3, +5, +12V
Front
Switch
(Norm.
Open)

Pushing the button then, leads to no reaction.

The +5VSB starts to flow, as soon as the switch on the
back of the PSU is in the "1" position. It's a Standby power
supply, keeps RAM powered during sleep, but also runs
the latch for the Front Button.

On page 37 of the PDF spec, section 4.5.1, you can see the
pinout on the 24 pin connector. With a slightly older supply,
the wires are colored, and the purple wire has +5VSB on it.
It's rated for 2 or 3 amps, and if shorted out, goes into
overload protection (no output). The nitwits who make power
supplies, put 24 black wires on the main connector on the newer
ones, making debug a PITA. Then you have to count pins, to figure
out which one is which.

Paul

On Sat, 26 Jun 2021 at 19:43:00, JAB <here@is.invalid> wrote (my
responses usually follow points raised):
>On Sat, 26 Jun 2021 20:31:15 -0400, Paul <nospam@needed.invalid>
>wrote:
>
>>You can buy "Port 80 POST cards" with two or four
>>seven segment LED displays onboard.
>
>Thanks for the tidbits....ain't no beeps on that computer...it's
>dead...no response.
>
Were there beeps when it was alive? If not, might just not have a
speaker/beeper fitted (-:
[]
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

.... the greatest musical festival in the world that doesn't involve mud.
- Eddie Mair, RT 2014/8/16-22

JAB wrote:
> On Sat, 26 Jun 2021 20:31:15 -0400, Paul <nospam@needed.invalid>
> wrote:
>
>> So that's a very brief introduction to startup.
>
> Tidbit - " [ Note: All these voltages will vary slightly for each
> combination of power supply, motherboard, disk drive(s) and various
> peripherals (since the number of electronic components drawing current
> alters a power supply's load), but its output voltages should never
> fluctuate upon reaching normal operating levels.
>
> If any of its outputs has an unacceptable amount of noise (or AC
> ripple[1]), then one or more of the motherboard's components, such as
> its Memory, may fail the Power-On Self Test, keeping the PC's
> operating system from ever booting up. ....]"
>
> <https://thestarman.pcministry.com/PCboot.htm>
>

This is hardly the best example, but it will
give you some idea how modern stuff works.

http://wiki.laptop.org/go/XO_1.75_Power_Distribution

Now, look down where it says "+1.5V_DDR3". There
is an LDO (linear) making 0.75V for VTT (terminator
voltage rail) and another LDO making +1.2V. They
appear to be powered from a switcher (MP28259).
Which in turn runs from "+VIN". On a desktop,
perhaps they would use the +12V rail for that.

https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP28259-A/document_id/3816/

* Wide 4.2V to 20V Operating Input Range [good for +5V or +12V PSU]
* 2A Output Current
* Low RDS(ON) Internal Power MOSFETs
* Proprietary Switching Loss Reduction Technique
* Power-Good Indicator in QFN Package
* Soft Shutdown
* Programmable Switching Frequency
* OCP, SCP, OVP, UVP Protection and Thermal Shutdown
* Optional OCP Protection: Latch-Off Mode and Hiccup Mode
* Output Adjustable from 0.815V to 13V
* Available in a QFN12 (2mmx3mm) Package

And that powers the DDR3 in that computing product.

The circuit can accept a large amount of ripple,
and the output will be clean. The package is 2x3 millimeters
in size. A mere silicon fart. The outboard components next
to the chip, will be bigger than it (needs an inductor L1 2uH).

Even a modern PSU has double forward conversion, so the
crossloading behavior has been mostly eliminated.

Mains ------ +12V -+------- +12V (many amps)
|
PSU converter board
|
+------- +5V (20 amps max)
+------- +3.3V (20 amps max)

The main +12V could have ripple.

If the +12V ripple was bad enough, it might corrupt a hard drive,
but then at some point PWR_GOOD would deassert on
the PSU if the swing was too much.

All the generations are different, in terms of potential
fault modes. The newer stuff is quite good now. I was
debugging something here one day, and my multimeter
was reading a number with several zeros on the end
(as a measure of how precisely it was regulated), and
I remember muttering under my breath "somebody is
showing off!". That's how good the regulation was.
At one time, they "just made the circuits work".
Now they can afford to show off.

Paul

On Sun, 27 Jun 2021 01:24:41 -0400, Paul <nospam@needed.invalid>
wrote:

>This is hardly the best example, but it will
>give you some idea how modern stuff works.

Many thanks....

On Sat, 26 Jun 2021 20:31:15 -0400, Paul <nospam@needed.invalid>
wrote:

>Assume the PSU is plugged in, the 0/1 switch on the back
>is in the "1" position and the PSU is on.

Rest of this story is the power button switch was broke

2 Pin SW PC Power Cable On Off Push Button ATX Computer Switch Wire
22inch Cord
https://www.ebay.com/itm/233974412750

thx again...

JAB wrote 7 months later:

> Paul wrote 7 months ago:
>
>> Assume the PSU is plugged in, the 0/1 switch on the back is in the
>> "1" position and the PSU is on.
>
> Rest of this story is the power button switch was broke
>
> 2 Pin SW PC Power Cable On Off Push Button ATX Computer Switch Wire
> 22inch Cord
> https://www.ebay.com/itm/233974412750

Not once was mentioned "would not boot" meant the computer wouldn't
power up when using the case Power button. "Boot" is a series of
dependent processes, not just pressing the Power button alone. "Won't
boot" could be, for example, the power cord (from wall outlet to the
PSU) is unplugged, or broken (severed wire), a power strip is broken, or
its Power switch or breaker/fuse is off, or the wall outlet is switched,
and its wall switch is off. Paul tried to make several suggestions, but
"won't boot" was too vague for him to narrow down all the possible
candidates for power problems, or all the points at which booting will
fail.

Paul mentioned checking if the PSU is on. While you could've checked
the voltages out of the PSU to check it powered up, a simpler initial
test would've been to check if its fan started spinning. If it did not
spin, the PSU was not told to come up (the PSU was verified usable in
another computer, so not a PSU failure). If its fan spun but
immediately stopped, that could be a PSU fault, like an overload on its
outputs, or a PS-On fault on the onboard logic from mobo telling the PSU
to come up. Shorting the PS-On pin (#16 pin, green wire) on the mobo
(with the harness connected from the PSU) to ground (either pin astride
of #16) tests if the PSU will come on when the logic on the mobo tells
the PSU to come up. The momentary case Power switch shorts that pin to
ground; else the pin floats high. Low = signal PSU to fully power up.

I didn't see your original post in the misc.news.internet.discuss
newsgroup, because I don't visit there. The Internet newsgroup
discusses PC hardware and operating systems? From the name of the
group, assuming I ever saw that newsgroup (doesn't look like anything I
would've searched on to find newsgroups), I would've figured it
discussed news on the Internet. However, after looking at it, seems
misc.news.internet.discuss is a personal newsgroup of yours to start
discussions (you're nearly the only one that starts threads there, like
you're posting your newsfeeds to there). In fact, your post to there
about your computer failure seems off-topic.

Glad to hear you got it fixed after 7 months. Next time, give details
on what is happening. "Car won't start" is also too vague, and can have
many possible causes, but doesn't even mention you turned the ignition
key.

On Tue, 1 Feb 2022 12:26:48 -0600, VanguardLH <V@nguard.LH> wrote:

>misc.news.internet.discuss

HISTORY: Tidbit

The newsgroup misc.news.internet.announce was created in November
1995, along with the companion group misc.news.internet.discuss.

https://groups.google.com/g/misc.news.internet.announce/c/f6gZlxu6x0o

misc.news.internet.discuss Discussion of news bulletins from the
Net
http://www.faqs.org/faqs/active-newsgroups/part2/

news bulletins - a short radio or television broadcast of news
reports.

See Also
https://www.mail-archive.com/misc.news.internet.discuss@googlegroups.com/maillist.html

On 2/1/2022 13:48, JAB wrote:
> On Tue, 1 Feb 2022 12:26:48 -0600, VanguardLH<V@nguard.LH> wrote:
>
>> misc.news.internet.discuss
>
> HISTORY: Tidbit
>
> The newsgroup misc.news.internet.announce was created in November
> 1995, along with the companion group misc.news.internet.discuss.

I take it that misc.news.internet.announce was later removed?