fixing an apple computer power supply
 

I yardsaled a 12.1 21.5'' imac mid 2011

at first try it posted an error screen with the hd not getting power
but then has refused to lite up at all

so I opened it up and tryed to check volts on the power suppy output
but finding a pin out for my exact model is not eazy [found same year 27'' pin out]
and I totally can't find a internal power supply diagram for this or any other imac

I find no 5v out at all [power for the hd]
and 11.87 v dc on the 12v lines is that near enough to work ?
and 3v on a line labeled pulse signal with no pulse just 3v steady

then checking ac input find the power button is not a 120vac switch
as power is always on to the PS 120ACV IN AND 12V [NEAR] OUT
SO HOW DOES A POWER BUTTON ''WORK'' ON A COMPUTER ?

being an apple all the parts are way over priced
a 205w ps is 150 new 100 rebuilt or 50 used
while a pc unit of the same power is 20 new
and I have no way to tell if the bad PS burned up anything else

Generally most if not all computer power supplies are switching power supplies, meaning they will show voltage but won't provide enough current to power up the circuit.

If you can find a power supply in the correct wattage with the correct mother board connector you could try running it external to the computer case.

I have propped up a few ancient computers with proprietary software that way.Ain't pretty but it can work.

They all have a slo blo fuse.

Check that first.

It's the first component in the power flow.

Follow wall power to where it hits the PSU.

Most likely it's a very small black box with the fuse inside.

Check it at the board for continuity

tim.id.au/laptops/apple/imac/imac_21_mid10.pdf

wish it was that simple
getting 12v out well 11.87 v
and 3.0x v is apple odd or should it be 3.3v like a pc power supply ?
but no 5v at all is there a fuse for each voltage ? or one main fuse = no power at all

thanks but I found the mid 11 [my] version here http://docshare01.docshare.tips/files/23542/235427388.pdf

but no pin out for my box found the 27'' mid 11

here

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

hope it is the same in my 21.5''
would love to find a real diagram of the power supply

The 21 and 27 PSU's are different.

I actually have one of each opened up right now.

I'd take pics for you but not home for a few more days.

If you can wait I can help you out.

And yes, there is always 12v at the power button.

Hitting it opens the circuit to the PSU which is why the slo blo is the first stop.

I would not worry so much about exact voltages that you are getting as long as you are getting readings the PSU is OK.

I generally recommend not opening those iMacs. They can be fiddly, especially the 21's.

Most common reasons they stop working is someone opened it to do a HD swap and broke a lead.

Really dead nuts easy to do on those things.

No power to HDD is usually someone borked the ribbon cable.

I get no 5v power right at the power supply pins
while getting 3.0 and 11.87 on the pins at the p/s
also tryed to check at the m/b power in and got power there also
but apple split the m/b power into two connectors and I have no chart or idea what pin # at the M/B unlike the 27 that has one power connector into the M/B
I think the link shows the 27'' not my 21.5 pin out at the M/B but the numbers match the 3v and 12v pins at the power supply of my 21.5 unit while the 27 power is in one block in at the M/B connector

27'' link https://d3nevzfk7ii3be.cloudfront.net/igi/moS64VEIPaD6QDkR
can you confirm that is the M/B pin out ? and if it the same as the P/S
as I am basing my hunt on two assumptions one the 27 and 21.5 P/S is the same for pin # volts
and the 27 M/B pin# are the same as the 21.5 at the P/S
that looks to be correct based on the volts at the P/S except for the missing 5v

apple appears to use a common ground for all volts to the #1 pin and no neg 12 or 5 v lines
that PC power supplys have



don't really need pic of the apple as the PDF has a lot just no diagrams of the pin# or schematic
of the M/B or P/S guts

a pic of the suspected ''fuse'' would help and where to get a replacement
I can solder and have removed&replaced chips on a tv CB before with success [with a net tutorial to follow]
no rush as I am still mucking about on this unit and have a working PC

found this bit on an other mac board

''There are quite a few things that can be wrong for a board not to boot. You know you have 3.4V on G3Hot so that is a good start. I would next check to make sure the 3.3V supply is putting out 3.3V. It is a dual port device with the other half putting out 5V but 5V is not enabled until later in the power up sequence.''

now that brings my 3.0x v reading on pin#6 that should be 3.3v in to question

but what I do not know is if it powers up later like the 5v bit looks to do

of course if I am reading it right and IF he is correct about the 5 v power up sequence

does a standard PC power supply out put all need voltages when turned on/plugged in ?
or do they also have a power up sequence where a signal from the mother board
is needed before all the voltages supply power out at the power supply ?

I am trying to understand if no power or reduced power ie my 3.0v on the 3.3v line out of the PS
is standard/normal along with no 5v power on a plugged in PS befores it get a signal from the mother board to go to full power in a power up sequence

as one rude and crude fix I could see is just wiring an PC 250w PS to the apple 14 pin power supply out plug for a $20 repair avoiding the apple tax $150 new unit price with a hole thru the back of the imac for the wires ether to test the imac to see if the MB is good or as a cheap lasting solution

but stupid me thought if you plug in a PS
it should out put the needed volts on the pins/lines
even if not hooked up to a MB ?
and with out no volts on some pins that later power up in a power up sequence

Yes, I think red 5v, yellow 12v, orange 3.3 You have to jump a few pins and if it's not connected, supply a load (resistor) to the 5v.... i use them for Plastic printers, etc.

Hopefully the power on sequence will not be a problem.

Here's an example: http://www.electronics-tutorials.ws/blog/convert-atx-psu-to-bench-supply.html

FYI, if you need cheap high current 12v (like to hook up heated seats in the house?) dell server supplies are cheap on ebay, and put out 50-60 amps. SmileWavy

Here is what you want.

http://tim.id.au/laptops/apple/imac/imac_21_mid10.pdf

Here's the mid 2011.

http://docshare01.docshare.tips/files/23542/235427388.pdf

thanks for the links

wish I could find a imac pinout for my unit
did find a same year different model Imac 27 vs my 21.5
but at the motherboard end of the power cable

27'' pinout at the M/b power connection https://d3nevzfk7ii3be.cloudfront.net/igi/moS64VEIPaD6QDkR

apple for unknown reasons or a whim splits my power cable into two separate connections/plugs on the M/B
unlike the 27'' model that I found the pinout for [at least some pins ] with all 14 pins on one plug
but it doesNOT list all pins ID's the 3.3 pin as signal no volts listed
I just hope the pin #'s match both between the 27 and 21.5 and at the motherboard end = the p/s end for the mid 11 imac's

finding lots of G5 repair kits for P/S or M/B with all new caps to replace

like this one [yes I know those willNOT work for my 21.5 intel box]
https://www.ebay.com/itm/Apple-iMac-G5-20-Power-Supply-P-N-614-0326-3350-New-Capacitor-Repair-Kit-x11pcs/190857766347?hash=item2c700265cb:g:8ycAAOxyFrNRv56 Z

for some unknown reason nothing like that for my intel imac

and most of the e-bay m/b ether doNOT have a chip or tell you what chip they came with
or are the slow i3 boards but few i5's and NO i7's
but a clue that many imac's FAIL THEN ARE STRIPED down and are parted out !!!
EVEN WHEN MOST E-BAY SELLERS ''CLAIM PULLED FROM A WORKING UNIT''
hard to understand why so many ''working units'' get pulled apart

STILL CAN'T FIND A PINOUT FOR THE p/s AT THE POWER SUPPLY FOR MY 2011 21.5
or the M/B power in 2 connectors

after turkey day bump in hope of ?

anybody know a trick to turn on a power supply out of the computer
so I can test the power levels withOUT risk to the M/B or other bits
and see if it really doesNOT out put 5v at all
and to check out the PC P/S before hooking it up to the imac

does apple really use one ground pin for all volts 3.3 5 and 12 v pin #1 on my power supply
and no negative 3.3v or 5v at all ?

what would happen if I used a PC p/s to feed 3.3 5 and 12v on the apple imac
as I have several from older PC's so a no cost test if it will not damage the imac
how to wire the separate grounds on the PC p/s to the apple imac ?

is a PC start switch the same as the imac ''power button'' ? the front push button not the a/c switch on the actual p/s box
will the imac signal start a PC P/S ? or is apple different just to be apple different ?
is the 3.3v line apple calls signal send a code or just voltage back to the power supple at start button push ?

I'll be back home later today.

I've got a 21 pulled apart and will take some pics for you.

thanks
just need the fuse/link area on the PS
as the pdf shows most of the other stuff just no pin out of the PS

and if you know how to power it up outside the box to test
or if it can even do that with out being hooked up to the m/b
also how to check the pc unit ps outside
and how to wire the apples common ground for all voltages to one pin #1
if I can adapt the pc unit I have to powerup/check out the imac

OK, the two black leads are the main hot and ground. Ground is the bottom, hot the top.

If the iMac is plugged into power you should always get 12V there whether it's on or off.

When not powered on you should not get any readings at the molex connector at top of PSU or anywhere else inside the case.

The fuse is the black cylinder just above the hot lead.

I doubt it's bad as you are getting readings past the main hot. If it were blown you would get nothing out of the PSU when powered on.

http://forums.pelicanparts.com/uploa...1511620055.jpg

Look to the right of the RAM slots. There are 4 diagnostic LEDS. How and when they light up can help you determine where the problem may be.

Check the Technicians PDF I posted for the sequence.

http://forums.pelicanparts.com/uploa...1511620308.jpg

As far as testing the PSU out of the case you don't really need to, just disconnect the molex at top of PSU and it will be isolated from the rest of the components. Check for readings at the connector.

thanks for the pictures

guess my fuse/link is good as it gets 12 and 3 volts out but no 5v at all
does the 5v line power anything other then the HD and dvd drive ?

but only one led lite is lit #1 and apple hid them under a cable
so not only does the screen need to be off you need to lift the ribbon cable to see them

minor correction 120v ac at the black leads not 12v dc
as that is power in from the wall plug

What problem are you having exactly?

Those boxes are UEFI meaning they will boot without a hard drive so no detectable power to the drive should not be an issue.

You should get grey screen and a flashing question mark.

Alternately you can try booting single user or verbose mode. hit power on then Command-S or Command-V.

The 5V is just a trigger / pulse signal to tell the drive to spin up. It's hit or miss to pick it up with a volt meter, at least I've found it to be a pain in the ass to detect reliably.

The hard drive gets it's power from the MB, specifically that cable covering the diagnostic LED's in my second pic.

at first try got a grey screen with lots of lines of error messages
kp = KERNAL PANIC i THINK

then a day later NOTHING NO SCREEN NO FANS ECT

TOOK TO APPLE STORE no nothing happened
they said bad P/S give us 150 to fix
then we can see what else it needs to be replaced !

so I took it home and opened it up
got 12v well 11.87v on 3 pins out of the p/s
and 3.05v on the 3.3 signal pin #6
no 5v on any pin should be on #3
no bulging or leaking caps seen or cracked solder joints found
or other obvious burned or broken stuff seen on the p/s

only saw one led lit #1 no others
HD 3.5 500gb loose like somebody messed with it seagate model barracuda has apple logo date code 11355
seller claimed HD bad

LED 1 is lit pretty much anytime there is power to the PSU.

Your readings out of the PSU don't sound out of range.

IIRC correctly the 5v are signals and may not read until the proper point in the boot sequence, meaning I don't recall it is a constant 5.

Bad PSU's don't cause kernel panics.

If I had to put money on PSU or MB I'd be betting on MB.

Those boxes are not uncommon and can be had (depending on configuration) from a reseller for as little as $250.

I'd not spend a dime on it but rather part it out on fleabay.

Like I said, they are fiddly beasts, I've seen people break them simply by replacing the HD.

If you want to keep investigating then start looking for readings off the MB connections and not just out of the PSU.

Unlike your standard Windows PC pretty much everything is powered off the MB.

If you've got 12V coming out of the PSU but no reading where power comes off the MB for the HD then that's probably your answer.

Are the fans kicking over?

Used ones are cheap. If you want to pm me the serial I might have one in stock

Also these are common to have gpu failure and it will act like the machine is dead if it really kicked the bucket.

Yeah but even with a dead GPU he'd still have diagnostic LED 2 lighting up. Says he's not getting past LED 1

If he's getting power out of the PSU at the molex but 2 is not lighting odds are pretty good it's as simple as a cable or the MB is toast.

Sidebar, you sell just full boxes or parts as well?

I own a repair shop and we also breakdown and part out machines for eBay.


A kernel panic then with lines on the screen again point to the gpu. I wouldn’t continue to waste your time. These are plagues with this issue. Part the machine out. And easily make a 3-400. Use powerbookmedic.com to get all the correct part numbers of what you have by serial number.

Sell the following.

Board and chip as a combo. Unless it’s an i7 then take the chip off.
Gpu. As is auction. You could take The chance of selling it working but I’m willing to bet it’s beat.
Display. How was the color when it was on? Again some have hazing and yellowing issues with age
Super drive
Ram
Glass ( not as bad as you think to ship)
Backlight board

Have fun.

paid a whole $10 for the imac
was surprised when it lit up and had a good screen with readable text
think I powered it on or off 3 or 4 times to the same screen grey error text

wait a few days tryed again now dead no lit no sounds fan beep ECT
so took it to apple still dead after several tricks by them
so took it home to open up
and began a web search on power supply for apple info
very little on how they work or repairing one R&R is standard only
fine BUT then I maybe back to a bad M/B for more expense

so first trying simple cheap tests like check volts with A VOM
tryed that at both PS end and at m/b power in but no pinout at ether end

for my exact box and I have not yet pulled the M/B so testing the back side pins
and can't even see wire colors to guess at what should be what
based on a numbered imac 27'' pinout of some pins at the M/B is all I have to go by
still searching but apple split the power connector on the 21.5 into two connectors in separate
locations on the M/B
while the 27 is all 14 pins on one I hope matching the 14 pins numbered on the 21.5 power supply

next idea is try to use a pc P/S that I have to feed power to the imac to see if it works
but I need better info before I try that

no real need of a imac or real desire after seeing how little info and high priced parts
and higher fail rates too to invest much ether

rather just buy and install a new M/b i7 and memory in a normal PC desktop
something I can do likely for about the same cost as this old imac would cost for the old parts

IMHO it's not worth any more of your time.

While a bad GPU could be the cause of its current problem it's in addition to the problem it has caused.

GPU won't come online until later in the boot sequence. You appear to not be even getting to that point.

So either the PSU is bad or the MB which is my guess right now.

Whatever it is at this point the likely fixes far outweigh the value of the box as a whole.

Part it out.

Or put it back together and I'll give you twice what you paid for it plus shipping.

I offer that because I'm in a similar boat. Had someone drop one off at my place after he broke it trying to install an SSD which I told him not to do.

I've narrowed it down either LCD or backlight but just like yours, it's not worth it for me to spend much, if any money trying to salvage it.

I collect and fix older gear because there is always a low income family or local congregation that needs a basic computer.

2 months ago I was able to outfit one of the local Sunday schools with HDMI laptops for their classrooms for essentially peanuts and my personal time.

My current pile of misfits I'm working on for donation.



http://forums.pelicanparts.com/uploa...1511708889.jpg


http://forums.pelicanparts.com/uploa...1511708946.jpg