PC power supply how they work

[nota]

I am trying to understand a simple PC power supply

they convert 120 ac to various dc voltages from 3.3v 5v to 12 v
to the m/b and other devices that bit is fairly simple and eazy to understand
as steady state power

but how do the signal to power up work some say a load is created on what power and how just resistance or a pulse or other ?
do the units send power to all lines and volts or have an order in which over time what is powered up ?

but the computers turn off or go to sleep on there own with other signals
how does that work ?

and to throw in a joker some M/B allow over clocking by raising some voltages on some parts of the system [but not others] how does that happen and is it in the P/S or independently on the M/B still head scratching on that part
the other joker is the NEGATIVE POWER LINES for minus volts what uses the minus side power and why ?

related and about my imac P/S problem but as few really understand imac/apples perhaps by design on apples part
I am trying to puzzle out the far more common PC power supply first

any help greatly appreciated

[stomachmonkey]

You are over thinking this a bit.

PSU's in general are not intelligent devices.

Think of it like this.

Plugging a PC into a wall is like hooking up to the local electrical grid.

Until you flip the main you will not have power inside the home.

Same with a PSU, plug it into a wall and you won't get power till you switch it on.

Once the main is flipped power is available in the home. Some power is available at all times, outlets, some is on demand, wall switches.

The PSU is not dissimilar to your fuse panel in that power is routed to specific circuits each with capability for different loads.

Some of the appliances you have plugged into outlets have their own power management, air conditioner, programable coffee makers, your fridge, none of them are controlled by the fuse panel beyond whether or not they get power.

That's pretty much it.

One of the primary difference between Apple PSU's and your general PC PSU is the Apple product is going into a known / static configuration where as a PC PSU has to accomodate for unknown peripherals.

Apple uses the MB to distribute peripheral power while a PC PSU in addition to routing power via MB has additional molex connectors "to cover bases"

Boot sequence, what turns on (or off) and when is not a function of the PSU, it's BIOS / firmware / OS.

That previous statement is generally true for all components except for things like fans that are connected directly to the PSU with no data connection to the MB.

Remember, all other peripherals, including intelligent fans communicate with the MB which tells them (via BIOS / firmware / OS) what to do and when.

[id10t]

You may want to look at the A+ Certification info on power supplies, etc.

CompTIA A+ Cert Guide: Power Supplies and System Cooling | Foundation Topics | Pearson IT Certification

https://www.lingq.com/lesson/a-chapter-8-power-supplies-2-683030/

https://www.certblaster.com/power-supplies-a-plus-901-sub-objective-1-8/

[flipper35]

On a PC there is always power to the motherboard and when you press the switch (or keyboard on some models) it powers on the rest of the board. When you overclock it and up the voltage it is using the MB voltage regulator for the CPU and/or RAM.

[nota]

Originally Posted by id10t

You may want to look at the A+ Certification info on power supplies, etc.

CompTIA A+ Cert Guide: Power Supplies and System Cooling | Foundation Topics | Pearson IT Certification

https://www.lingq.com/lesson/a-chapter-8-power-supplies-2-683030/

https://www.certblaster.com/power-supplies-a-plus-901-sub-objective-1-8/

thanks
the lingq link was very good and explained most of my questions

but
still do not get the NEGATIVE VOLT LINES and what they do or are used for

and how the M/B tells the power supply to turn on/off after you press the momentary
switch/button that one can short on the m/b to turn on but then the M/B sends ????
to the PS on what line ?
as I need to test if the PS or the M/B is bad so need to trick the PS out of the unit to normal operation to test it

[flipper35]

There are two pins you short to tell the power supply to power the rest on. DOn't remember which ones.

[flipper35]

[nota]

if I am reading that picture correctly

pin #16 green [and green wire] to pin #17 yellow in the pic but a GROUND PIN [so black wire]
I think on a 24 pin connector
IF THE BLUE IS#20 AND NOT USED
should be same place on a 20 pin connector but # 14 to 15 pins [I hope]

THANKS

[flipper35]

Many of those connectors are 20/24 pin. The end comes apart.

[stomachmonkey]

This is a 21" iMac PSU. If yours is different post a pic I likely have one.

If it's this.

This is a known working PSU.

1) Plug into wall power but do not turn on the iMac. With your voltmeter you should read ~120 on the pin in the lower right red circle. Ground is anywhere on the chassis.

2) Check any of the pins from left to right in the yellow box upper left. They will read 0 if you did not turn on the iMac.

3) Now turn on the iMac and check the pins in the yellow box. From left to right they should read roughly.

0 12.1 0 2.3 0 0 12.1 12.1 12.1 0

If that's what you get and diagnostic light 2 also does not come on then there are only two possibilities, an issue with the cable between the PSU and MB which is unlikely unless it was taken apart at some point and botched on reassemble or most likely the MB is bad.

Part it out and move on with life.

[nota]

no my board has a 45 deg cut at the end where the power pins 14 of them are in a double row
pin numbers are printed on the cb 1 7 8 and 14 have to count the others
but the power out cable splits to the M/B into two 6 pin plugs that I have no info on
only found a imac 27'' m/b end power cable pin out those # for 12v lines and a 3v line match my PS out readings
again no 5v on any pin ever found

my unit looks like this e-bay ad and both numbers 614-0445 and dates mid 11 match

https://www.ebay.com/itm/Apple-iMac-614-0445-205W-Power-Supply-Replacement-For-A1311-2009-2010-2011/263322971218?epid=1105703655&hash=item3d4f45ac52:g:JqAAAOSwVNxaCx6w

[stomachmonkey]

It's, IIRC, 5A.

If you are looking for 5V, you won't find it.

[nota]

Originally Posted by stomachmonkey

It's, IIRC, 5A.

If you are looking for 5V, you won't find it.

well PC's run on 3.3 5 and 12 volts from power supplys
sata power has 5v as do several other cards and drives

do apples run on magic smoke with out a +5v dc line ?
a 20 pin PC m/b ps in plug has 5 separate +5 volt dc in lines and one other labled 5v standby
a 24 pin has an extra 3.3 5 and 12 plus a ground total 7 +5volt lines

my found 27'' pinout claims apple has 1 count them again 1 5volt power out line

[stomachmonkey]

Originally Posted by nota

well PC's run on 3.3 5 and 12 volts from power supplys
sata power has 5v as do several other cards and drives

do apples run on magic smoke with out a +5v dc line ?
a 20 pin PC m/b ps in plug has 5 separate +5 volt dc in lines and one other labled 5v standby
a 24 pin has an extra 3.3 5 and 12 plus a ground total 7 +5volt lines

my found 27'' pinout claims apple has 1 count them again 1 5volt power out line

Now I don't recall the spec of every Mac ever made off the top of my head, most, not all.

But yes, some of them do not output a dedicated 5V. They use a step down voltage regulator down the line.

You keep trying to equate them with standard ATX power supplies that may be used in PC's without knowing if a step down regulators are present which requires the PSU to have a dedicated 5v output.

They are not the same animal.

Remember that an all in one like an iMac is somewhere between a laptop and desktop.

Laptops have external power supplies with one wire supplying voltage.

Does every component inside the box run on the same voltage?

No.

[nota]

https://d3nevzfk7ii3be.cloudfront.net/igi/moS64VEIPaD6QDkR

that is the ONLY PINOUT I have found for an Imac near my unit
same year different model mid 11 but the 27'' not my 21.5 and at the M/B end of the power cable
but same 14 power pins and the 3 and 12v lines are the same pin # when I checked with a VOM
I got the reading at my PS out pins
ground is the same #1 and nothing on the unlabeled pins
it shows pin #3 is 5 volts for HD[s] that is my one data point
that is all I know

and yes I am trying to understand if a PC P/S can be used to power an apple imac
I like cheap fixes and likely have wasted more time on this then it is worth
but hope to learn a bit by doing so

I am trying to learn
and greatly appreciated your help
all I know about imac and PC p/s I have learned following links and asking questions

[JFairman]

PC power supplies send some power to the MB when they are plugged into the wall while the computer is turned off. I have an ASUS MB with a red LED that lights up if the power supply is plugged into the wall.

USB ports supply 5 volts. Some have enough juice to charge a cell phone and others don't, and that may be more of a laptop thing.

By far the most versatile and productive computer is a Hackintosh with Clover boot loader software installed.
https://www.google.com/search?client=aff-maxthon-maxthon4&hs=S25&affdom=maxthon.com&channel=t3&source=hp&ei=58MeWv7XBYzEjwTB4ZCoBw&q=clover+bootloader+windows&oq=clover+boot&gs_l=psy-ab.1.1.0l10.917.5363.0.12717.12.11.0.0.0.0.174.127 8.0j11.11.0....0...1c.1.64.psy-ab..1.11.1277.0..0i131k1.0.dofKuQOyFQY

With that you can have MAC Sierra and Windows 10 Pro on the same hard drive and you click on which OS you want to start up.
Use a solid state drive so it's fast and use your old mechanical hard drives as backups. You can clone them perfectly with Macrium reflect which is a free download.

[T77911S]

Originally Posted by id10t

You may want to look at the A+ Certification info on power supplies, etc.

CompTIA A+ Cert Guide: Power Supplies and System Cooling | Foundation Topics | Pearson IT Certification

https://www.lingq.com/lesson/a-chapter-8-power-supplies-2-683030/

https://www.certblaster.com/power-supplies-a-plus-901-sub-objective-1-8/

that A+ cert was a joke.
work made us do that years ago, in fact the book is still on my desk. they sent us to class that did nothing but teach us the test, literally.

I remember one of the things they stressed,
if the fan goes bad on the PS, don't replace the fan, replace the PS. (stomp stomp) test question and answer.

[stomachmonkey]

If you read into what the chart says about pin #3, .....Note: If present the 12v will come.....

As in, it may not be present, it may be a variable, option. It's a conditional statement that may not always be valid.

I read it as, "If not present 12v is not coming directly from the PSU".

Being curious I opened my 27in.

Known good PSU and logic board.

Checking voltage at the PSU, 0's 3.3's and 12.1's

Now the interesting part.

Checking the diagnostic points on the MB, I get a 5.

There does not seem to be a 1-1 correlation between PSU pinouts and the MB diagnostic pinouts.

I have to admit I found that rather surprising and counter intuitive but I checked it several times and it is what it is.

Somewhere along the line 12.1 PSU output is being stepped down to 5 at the MB.

So that chart only seems valid for checking power at the MB and that 5 is not found at the PSU really tells us nothing.

Your PSU and the one I just tested are only 1 revision apart.

It's highly unlikely they'd be radically different as the changes would have a cascading affect throughout the system.

Too much would have to be updated to make it worthwhile to eliminate 5v at the PSU.

I'm 99% confident your PSU is fine.

[nota]

while the imac just maybe like a laptop with 12v only need input
why then 150 price on a 14 pin out put P/S when a simple 2 WIRE 12volt LINE only is all it needs ?
AND HAVE 5V LINE ON THE PINOUT ?

most all non -laptops uses 12v, 5v and 3.3 volts lines a standard M/B has 6 total 5v lines
not counting the drives power SATA3 or usb lines THAT USE 5V ALSO
SORRY i THINK WHILE APPLE IS WEIRD THEY AIN'T THAT WEIRD

[stomachmonkey]

Originally Posted by nota

while the imac just maybe like a laptop with 12v only need input
why then 150 price on a 14 pin out put P/S when a simple 2 WIRE 12volt LINE only is all it needs ?
AND HAVE 5V LINE ON THE PINOUT ?

most all non -laptops uses 12v, 5v and 3.3 volts lines a standard M/B has 6 total 5v lines
not counting the drives power SATA3 or usb lines THAT USE 5V ALSO
SORRY i THINK WHILE APPLE IS WEIRD THEY AIN'T THAT WEIRD

I have no idea what you just said there.

It reads like drunk Yoda.

One last try.

You are unfamiliar with this PSU and would like some advice.

You keep looking for 5V out of the PSU because non apple PSU's have it and you have a schematic that shows 5V at the logic board.

I have several known good Apple PSU's in the same family as yours, older and newer, and none of them output 5V at the PSU.

The only place 5V is read is at the logic board which is explained by the use of voltage step down regulators which we know are used.

Still, despite all that you want to keep insisting there should be 5V output at the PSU?

Just so we are clear, the earth is not flat, we did land men on the moon, Santa Claus, the Easter Bunny, and the Tooth Fairy are not real.

OK fine, you're right, your PSU is ****ed, is that what you want to hear?

So either suck up the $10 loss or go get a cheap ATX psu, try and jerry rig it, keep banging your head against the wall, waste more time and money.

Good luck.