PC secrets learned the hard way, by using meters and scopes and even laser tachometer.

Most of what I have here are problems with factory OEM PC's, not found on DIY PC 
(<click link for quiet PC builds)

Scope;  10 year old PC.s or less. 2010 to now.
This page is for all things beyond, normal standard parts in a PC, Like normal common USB devices, PCI-e cards, Monitors (VGA/DVI/HDMI &Display port), SATA port. That are all standardized.
I will also comment on NOISE, + overheating and all cures, and what computer cases to buy.
 
This page covers alien (queer non standard jacks/plugs,etc.) used by OEM makers of PC,  alien grade PSU, and motherboard and all those alien gold pin header ports seen on the mobo (motherboard)
Some Audio ports and USB3 ports on the mobo do have the 20 pin (10x2) Intel standard USB3 or audio
Some PSU  connectors all wrong,  and worse missing, PCI-e Aux, GPU cables. 6/8 pins. (means fast GPU cards can not be used lacking these 1 or 2 power cables)
The whole PSU is alien on many makers of OEM PC's...  (if wise build your own PC DIY)
The one connector that is not documented by the OEM;s is  power on switch , Power LED, HDD active, and error LED.  (at Asus.com or Gigabyte.com we have NO lack of documents this topic) OEM are the problem.
Intel did this for years,  most OEM ignore it and even add Bipolar 2 color LED here and HDD/Post code error and activity and reset is no GONE forever.
Some PC makers add LED here, even 3 of them for Diagnosics and HDD activity and for Power is on status. RESET IS NOW OBSOLETE, a legacy bad Idea now gone.
Vast versions of this simple function exist, in the PC world and no standards exist. (but with hard work we find the answers)

If you DIY made your own PC this is never a problem ever.  (hint#1 max)
The worst PCs are called BTX form factor  PC's and best is to avoid them all.
The best place to ask for pinouts , not Dell or HP forums they will tell you it is all this very odd and bloody secret.   or look here first  PINOUTS.RU.

First are my DELL PC's (desktops only and only MT mini tower, never will I touch any SFF, DT or micro cased PC's) but yes just below shows SFF.
Not picking on dell, most OEM makers do these tricks, all or some.  (Asus.com mobo use spec parts so I buy those mostly)
The mobo has 24pin power jack. but is non ATX spec, and a micro sized, so to use  new ATX PSU you must  buy an adapter first.
The black socket it the warning sign (queer parts). Non SPEC. Wrong socket used (size) and wired wrong both , do not blow up a good mobo wiring this up backwards.

A $10 -$10 cost ebay or amazon.


As you can see Dell even scrambled the wires on pins, just for kicks.

The secret power on JACK: on real DELL XPS DESKTOPS (prime)


The 9810,20,30 PC uses this power/LED switch and pinout secret.

The newer 8900 series does not use a standard mATX rear mobo I/O shield,.  1.75" and 6.25" long, but uses this lame glued on shield. ( I will show more on this later ) first seen on XPS-8910 chassis (case)
Why is that important?, easy, one can upgrade (swap) case or mobo with impunity, (a gamers dream, and real if you build your own PC) The ATX spec and mATX documents  even tell of this dream (real at Asus.com)
A well designed PC mATX can use any mATX mobo and real ATX PSU or real TFX PSU, no need for queer cases or PSU, ever.

Dell 3020/9020 MT Optiplex  secrets and others see link here>.   We use this adapter from ebay or amazon.

Many of these PC newer have all black wires now, making gamers happy (they hate colors) and OEM richer , all black is way way cheaper wire. (and sucks to any tech)

Many modern Dell Desktops with the 3x2 , 6pin plug with pin 1 bocked uses this schematic.

Common on Dell PCs 5-10 years old. (corrected errors my edits)



SEE MORE SECRET PINOUTS HERE,   VERY GOOD, BUT NOT COMPLETE, NO WEB SITE IS,,,,    Pinout.RU

2005 era, old. This is no standard it is DELL only.


Here is my 3020 MT (mini tower only)circa 2013 with the non standard jacks all disclosed. (a real nice PC it is and fast) (seen on  7020 and 9020 Optiplex)
The RED STARS are custom alien proprietary connectors, why a secret? , no person on earth can guess. These comments are for the mobo side, not the other end of cables (like USB)
My PC below has  J18 power adapter to a new huge 750watt PSU ATX spec. for over 3 years now. zero problems ever.  J18 is NON-STANDARD DELL ONLY.

If the wrong fan is used, even pin counts right the alien fan may fail the RPM test if it does not  work like the OEM expects in BIOS.
end dell.



HP non ATX wiring  horrors of  PSUs
Seen HERE:



Other Pin headers do have  a standard (if OEM cares)  even by Intel for for sure USB3, panel cables and front panel audio ports MIC + Phones (L/R)
I call this a quasi standard, as many OEMs do not want to use  them.  Intel is the guiding light here ,but OEM makers love to go wrong here. (astray)





See Fan tricks,  ( huge variances exist, 2wire ended decades ago) Below are common today.  (makers, using wrong color for RED I say Dang man really why did you do that)?

All my comments ,Assumes room temps not over 95ºF. ever.(as the PC  maker told you)
I will show solutions for all cases but not water cooled, but the cases sold for water cooled ready are the best cases (chassis to buy).

This works. (plugged in backwards trick) do so with care. Some PCs use totally different rules here, wild it can be.  (use the right fan and avoid errors here)
The 4 pin fan, some fans will be dead with a floating blue wire,  and some mobo will fail and does so because it checks PWM against real RPM from the tachometer pin and if not a match (say with-in ±25%?) you get POST errors.
PWM is  a  Pulse Width Modulated signal from PC to FAN, that sets and exact speed. (BIOS sets speeds not you) The BIOS computes RPM wanted and sets PWM to the correct value.
For sure  3wired fans are now mostly Legacy. (make sure pin2 is the only pin with 12vdc)  Some fans will not spin with pin4 open, but most of mine here do spin full speed.
Never allow 12vdc to be forced onto pin 4, in any way or the mobo blows up or fan, depending how you did that wrong. (pin4 is  5 volt digital input to the fan. (only)


Not all 4 pin fans are wired  the same nor  are 3pin, (factoid#1) You must do your own home work (measure pins with a voltmeter)
The TACHO RPM  read (& sends) correctly 2 clicks per turn. (or BIOS fan monitor gets all upset on OEM PCs using the wrong RPM fan.)
Factoid #2, if you hack the connections the fan will just scream fast and not run as the BIOS wants.

4:3 hack #1:
 The 4 pin mobo to 3 pin trick that fools the motherboard, and  can be tuned ! R1/R2 ratio. (tuned until RPM Tach pin, reads correctly on pin 3)
 The fans are really 3phase AC fans (a.k.a Brushless) or more and phase locked to PWM. The below is crude, but will work.  It modulates 12vdc in to the fan.


Now my yellow wire (RPM) trick:
(used on any failing fan for RPM BIOS monitors)  (wrong fan used trick)
The problem is simple the 2nd fan runs at wrong RPM (3wire) and fails BIOS checks.(POST errors out)

My old PC mobo, the  3 wire CPU fan works perfectly, but the 2nd Case fans is the wrong fan , too slow or too fast RPM.
I then lie to the BIOS doing this:
I jumper wired the CPU yellow pin (tach out) to my  failing  case fan (runs ok) bios failure,  I cut the 2nd fans yellow wire and jumper it to the good fans yellow wire. (then 2nd fans yellow pin is now useless)
This is how you lie to BIOS (tacho) CPU yellow out pin3 >>>> jumper to>>>>>> Mobo case fan yellow wire input  to MoBo..pin 3. BIOS is fooled.

DIY methods both:
The other solution is to use only your own fan contoller card, (mounted to blank space in the case) and it has thermostat or POT, that runs fans any way you want or buy Asus.com MoBo and it allows the user to set their own fan speed /temp profiles.(4wire)
The problems with OEM PCs it loves to set errors if the fan is not their exect spec. fan. (intractable. see hack above yellow wired)
The modern PC , non OEM (many OEM block access to speed) we can run "SPEED fan" to control speed of  the fans. (4wire)

If you hate LED fans like me , sure buy them lacking any LED, but here is a simple  cure.  Fans with LED on the outer rim are easy to cut, but if inside the hub,  a royal PITA that.
This common wiring, even 6 LED in series,  because the motor needs full 12vdc to go full speed.  Thus this method is used. Just one cut and Dead. (yellow is red on many)
The best fan that can turn off  LED's is like this one sold on ebay, with its own controller, and OFF LED is choice. (as in the case (no pun) that case came with 2 or more fans with LED)


BTX PC's to never buy ever. (legacy now) all use a non standard CPU heat sink fan and hoods, and the silly motherboard is mounted backwards, (right side) and forces any GPU card to be upside down and that hits things (hard fail)
DELL Optiplex, XPS and Dimension numbers, 330,360,,380,755,780,760,790,960,980 and XE, GX520,GX280,GX620 AND
, 3100-e310, 3100, 5150, 9100, 9150, 9200, xps 200s/210/310/400/410/420/700/720, E520, E310, at the least


HP made only a few. Dimension 5100?, circa 2005 made, Avoid BTX PCs at all costs. DEEP SIX them. (a door stop or a boat anchor) or
HP Elite 8300 ouch.  Mostly 2004/05 junk sold then, not now.
How does the " power on button"  work ?, using all Intel south bridges here is a simple answer.
The user pushes a button marked power, seen pin 6 below, and goes to 0volts ground , this signal goes directly to Mr, South Bride chip, my Z270 does the same.
If you do that the South bridge chip sends PWR_ON command to the PSU, and the PSU sends back I am ok and the PC stays running.
If you hold the power button for 10 seconds the PC does a hard reset, ending sleep mode and more.
On newer PC this is the Intel PCH chip.(ICH old name)

The PC can turn itself off in 1 second or less, due to any overload of any kind, even PSU overheated or mobo VRM modules overloaded. (The PSU can overheat or overload too) PSU fan Dead?

Standards common to any "PC" (the more standards used, the  more fluid are upgrades even Case swaps or MoBo swaps super easy. (OEM PC's fail hard here !)
Next time buy the MoBo from Asus.com  like a fine,  z390 prime.(RTM read the manual and wow all pins defined)!

Form factors:

ATX PSU 2004 era , there are much newer docs. but costly to buy.  How does  PSU work? answer: see 2007 schematic here, ver good !

My PSU uses these connectors besides SATA Power 15p. , and GPU aux power plugs for powerful fast GPU.   The  4 pin flat (SIP) Molex power plugs seen on year 2000' HDD and DVD drives are now very obsolete.
If shopping for new PSU always by what is called single rail PSU, most are now. (500watts min)
To bench test any PSU just jumper green to black 15 to 16 pin with a paper clip unbent.

Modern PC + PSU are evolving fast  to ATX12VO SPEC.(10pins)  Why they did not re-purpose old legacy pin 20 (-5v) I do not know. But less copper waste is good. (and less cables/bundled size sure.)


ATX  Chassis  (and  the mATX ) case chassis standards.

USB

PCI-Express slots x1 to x16 lanes.

SATA.  ports for HDD / SSD or DVD (ODD) drives. Most are SATA-  3 GRADE NOW, "PATA" DRIVES ENDED BACK IN 2001.  (lets forget  PATA)

Q1: Can I use any SATA drive made in this PC?, sure,  That is what SATA is all about,  a standard interface used from 2001 to now. (if running windows 10 64b bit there is no limit you can buy now or for 20 more years)
The only limit is using the wrong format and landing on the  32bit OS limit called the  2TB limit, (two tarabyte) a not true limit if you learn to use the format tool app properly, changing the cluster size. to 2k  or 4k.
"32-bit XP can support up to 16TB drives. The cluster size simply needs to be changed from 512 to 4096"  but can not be the boot drive, unless.....
No 32bit OS partition can be over 2tb (32bit rules). So if you have a 10TB drive, you will need to split it up into 5 partitions of 2 each.. and the first one is the boot  partition.

DVD now mostly obsolete is SATA port connected 2001 to now
Floppy drives, what are those? , those ended 2 decades ago , forget them. RIP.

CPU: best is itel CORE GEN 4 up; (never less) i3-4xxx ( i3 up and 4xxx up)

CPU SOCKETS At Intel.com are a stardard by them and AMD too has processors and their very own sockets. (Intel has vast CPU and lots of sockets for mobile , desktops and embedded systesm (like ATM)
Here is mine for 9th Gen, 8th Gen, 7th Gen, 6th Generation Intel® Desktop Processors use LGA1151 socket.
Just because a CPU fits the socket does not mean it can work there,  your South Bridge dictates GENERATION of CPU versions (speed/cores) it can use not you ever. (and BIOS versions and maker of PC)
Asus and Gigabyte both publish QVL list for all CPU and DDR memory that is certified to work, no OEM DOES THAT THEY ARE TOO CHEAP OR LAZY OR IDK WHAT.? (QUALIFIED VENDORS LISTS)
See my horsed up LGA1155a photo.
The GENeration CPU must match the Mobo.  if wrong socket, there is no forcing pins, (like IQ tests with round peg and square hole)?

RAM (DDR memory DDR4 is now.


CASE FORM FACTOR AND Motherboard (MoBo).
OEMS LOVE TO USE THE SMALL MOBO TO MAKE MORE MONEY AND HAVE SMALLER CASES. (then wonder why gaming GPU  cards overheat all things inside) Wiki link mATX.
My Dell XPS-8900 uses this mATX mobo form factor. (and case and MoBo)  and this,  shield
Ignore AGP slot,  top brand ATX cases  now have both ATX and mATX mounts.(by design and intent)

Parting shot, the best case is the case the runs the coolest (ATX) and makes the least noise gamed max. (looks be damned) The life spans of electronics are short running too hot.. (huge fans 120mm+ are the best , run slow and high CFM)
Intels old spec, on mATX is here, free to have read or  share. ( a.ka. uATX)  This spec is 2004 , over 17 years old now, and still going STRONG, thanks to Intel.com.

NOISE and overheating related causes and cures and does relate to form factors and choices by you, buying  new PC or DIY. (by gamed I mean just that or any high end fast powerful 3D GPU app. of anykind, even CAD/CAM/CAE or video editors)
First off they do sell fans that are super quiet below 25dBA, but are lower RPM (to be more quiet) and only 1/2 the CFM airflow, so if that floats your boat or for sure does not allow overheating, then this is a goto fan.
The grand conundrum?,  on one hand you want quiet and on the other hand you do not want a burned up PC. (overheating any PC causes a short life span and throttling or even self shut downs)
  1. Bad fate, the fan is bad (bearings shot or a broken blade) or loose mount (tighten it) or wires hitting blades of fan. (move them)/
  2. Buying any PC with fans below 120mm (4.7") will be very loud. (gamed)  Big Diameter fans are best. (even 140 and 200mm fans exist)  Big fans can turn slower for same CFM and are whisper quiet. (the whole industry (DIY)is going there now)
  3. A modern PC runs the fans slow until you game (PWM fans, 4/5wired are best)   if you must run 3wire buy low RPM fans 1200?  (a loud  2800 rpm fan will be loud 3wired but 4 wired only if PC commands this speed via PWM)
  4. A PC that is too small (like all low profile cased PC or SSF or micro cases) will be very loud,  gamed, faster speed RPM.  Do not buy these PC.'s (if you do not like noise, next time shop by NOISE top of list, aka,acoustic spec.
  5. Any PC with 120mm 3/4 wire fans can be found that make less noise shop by noise levels -DBM(A scale) some turn slow and flow 150 CFM (cubic feet per minute) of air, choose fans carefully. (special blades to make less noise)
  6. Don't  buy a mATX / uATX full height case as the makers case is very small like my Dell XPS 8910, they made it so small and load noise, I had to use 3 case fans to get it cool. (using all tricks in the book)
  7. Buy a GPU card that is only 75watts max like GTX1650 is. Do not buy 350watt GPU cards then stuff it into my 8910 (LoL) and expect cool to happen, it will NOT.
  8. Buy a  GPU card that is double wide with its very own air port on the rear to send all its nasty heat directly out of the cased PC. (also some GPU cards are load so some have 3 slow fans to be more quiet)
  9. Some cases are so poorly desiged (uATX) that the air paths are blocked by GPU card (long) or PSU or both. Then what ever space is left is jam packed of cables,so buy a modular PSU. PCs that overheat run fans too fast and make too much noise.(see why lint does too)
  10. Some Cases have a PSU that only sucks air from side of case or the bottom case vent and keeps PSU cool and lasts far longer that way.
  11. Some better made cases do not buck thermal convection.  Top vented and with fan blowing out the top is best. A very smart idea that. (bottom vents too and front) and again fans run slower not overheating.
  12. Upgrade fan screws to use new rubber pin mounts gains you less vibrational noise. (they streach to fit)
  13. Do not buck fans, 2 pushing air into the case, make them all suck fans or push pull, never buck them.  (try to help convection not buck that either....)
  14. Go water cooling "ready" upgrade. (some are fan less,with external cooling towers)  and some are near dead quiet all the time. (but are not cheap done right) or just this.
Avoid this kind of GPU CARD  on the left, a  350 watt GPU with waste heat  dumped in to the confines of the CASE.  To to this you need 3 case fans at least. , the card on the right does this correctly. (but the fastest made cards can not do this)

Even worse the card on the left sucks its own heat load out. (the loop of hell that)....!!! yea lots of case fans, and more to cure that  problem...

Heat loads max, a worst case and for sure a hard job to do right.... but showing extremes, all else is a cake walk.
GPU 350-watts, like RTX3090  (if not kept cool it will burn up or shut down from internal overheating controls in the GPU logic)  The CPU too shuts down too hot or THROTTLES itself.
CPU at 150+ watts.  like
Core i7-3970X
PSU  100watts (20% of 500w is....) make sure PSU  exhausts all its hot air to the rear of PC and room.
Mobo watts, about 25w. (south bridge and VRM heat)
HDD about 12watts (1 amp)eacg startup is 2times that.
SSD , tiny even 1watt,

One cure for 350watt ROOM heat Blaster GPU card is this new PC case with 200mm fan up front and more inside. Call it the wind tunnel. (as seen on Ebay)
This fan is more quiet too. Some fans 200mm are
700 RPM 110 CFM . more quiet and more CFM.
Midtower case, good. Full towers better:
Click image to zoom it. And here.

Better is a full tower for those that want max cooling with endless choices of fans and speed off fans and for sure NOISE of fans Quiet.  (I take my wire cutters and cut the LED leads to kill detested LED , just for kids and never me.)
Click image to see ebay sellers

Picking a case, besides looks takes great care.  
ATX or mATX case.  or even EATX) my list only.
The POWER OF TOWER:
Water cooled ready !
The full sized tower in EATX,ATX, mATX mobo, can run cooler that is a fact. ( lots of space and lots of huge vents is a win) Desktop that are super crowded insite run hot and fans screem loud.
Must have top and bottom huge vents (grill) and huge fans. 120 /140mm or larger. (present or places to put them , as in ready mounts) large fans run quiet.
The PSU is on the bottom and sucks air in the PSU tunnel there and exhausts all of its heat load to the rear of PSU, and never to the main case. This helps the PSU last longer , having cool air induction vent not hot from case.
The quanty and type and size fans is your choice but is best decided first buying the correct case. ( the photo directly above is a winner)
Full towers (or mid) are best (never me seen any actual study desk made that any tower will not fit) Why fear ATX, I've no clue, sure School dorms... sure...
A motherboard with 4  PCI-e slots is best, so you can add cards later. ( always plan for the future?)

Conside water cooling  now ir in the future (water ready)   this option also allows huge top fans or water radiator   and has a huge grill up top.
Fill height and length GPU cards fit, even 3 fan GPU cards fit even 12" long.
Watch out for silly cases that block the PSU bottom PSU fan vent portal, not good that, ever.(unless bottom case vent matches PSU fan vent)
Buy the case first, and is   near infnity now. (choices)
One silly trend is ,usb and audio jacks are on the top not front or left side. DUMB IDEA alarm. (but  I can  live with it)
I like maker NZXT or LIAN seen on Amazon, and the 200mm fan PC above.
I have no use for RGB , LED fans  , I defeat all RGB I find, but sadly many cases are preloaded with stupid RGB fans and no off switch amazing as that is , but true and I find the LED power source and cut it out. with cutters or buy new fans devoid of this BS.
 
One more cool feature is the right side comes off too, and that whole offset area there is for you to hide cable. (like it!)


Last what are good low cost used Dell fast tower desktops, (well below $500 used) Only full sized case are good so any PSU and GPU card can fit. MT is it.(mini tower named)
The answer is, with ATX sized PSU, but none are ATX cable ends. (using $6 PSU 24/8 pin cable adaptor
Optiplex MT all ,  3020 up, like 7020,   9020 (  9020 best, gen 6/7 CPU best)   other PCs have narrow non ATX sized PSU.  All the good ATX Dells need the adapter but that is not a problem ever. (no sawing huge holes in the case means fits)
 
The T3620 MT Precision  is also great, with ATX case too, but with adapter above .,
My XPS 8900 has real PSU. 8910 to 8930 do but not higher numbered models. My 8900 runs way to hot gamed. full fans opted. sadly.
There are more Dells called Inspiron,  game class , that have ATX SIZED PSU, and even real ATX cables too.. and not new $3000 PC's
Those are:  3670 , yes ATX but 8 pins.Gen 8 CPU.
The Inspiron 5680 is near ATX  sized 460w and will allow real ATX PSU to physically fit.( the problem is the fan on some ATX go down in this PC, do not buy those!)ATX suck fan must be on the top ( and ATX mutation by Dell).
The PSU that fits is this series 
EVGA SuperNOVA 650 G+,  the rear mounting holes are genious class !. fits both ways it does ! Super NOVA G+ any watts.
Exhaust is on the rear, on all ATX PSU. Suck ports wrong is a DELL thing for BOTTOM located PSU's. (suck = air induction port)  My DIY PC has case with bottom suck port. That means natural PSU's work from top PSU classic ATX style PSU.

Dell and most others love to shrink cases and that flies in the face of bad aircooling and then overheats gamed. (small cases can NOT BREATH nor allow even 2 case fans to fit nor flow air correctly or does so with very loud fans screaming like mad.)
As seen here. By EVGA ! maker of PSU as seen on NEWEGG.com , seen only on G+ models.  and 80+
EVGA G+ PSU, dream PSU. fits any PC made !true ATX




The guy that says ATX is useless and only 1995 is full of crap ) , Intel keeps upgrading that spec,  2004 and more. They even have the new 12ATXVO PSU spec too. 2020.
The ATX specifications were released by Intel in 1995 and have been revised numerous times since. The most recent ATX motherboard specification is version 2.2.[2]
 The most recent ATX12V power supply unit specification is 2.53,[3] released in June 2020. EATX (Extended ATX) is a bigger version of the ATX motherboard with 12 × 13 in (305 × 330 mm) dimensions.
An advantage of having an EATX motherboard is dual CPU socket support. (WIDER Mobo)
ATX is a de facto standard as wiki clearly states.  (over 10 revisions )
There is no harm with makers like EVGA (God speed) to make a SUPER SET versions. (for sure Biopolar screws holes and for sure SINGLE RAIL 12vdc) Plus ! built in fan controls for heat even quiet fans until a PC gets too warm and even more overload protections.!!!
You do get what you pay for in a top grade PSU ATX for sure.

or?
A DIY  PC best is first the case then buy mobo, GEN6 CPU up or Z270 up chipset, USB 3 min, PCIe-gen3 min.  and 3 or 4 PCI-e slots. DIY has real PSU's for  sure, and full DOCUMENTATION,  amazing that.

version3.  4-1-2021