fixing an apple computer power supply

[nota]

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

[scottmandue]

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.

[stomachmonkey]

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

[dad911]

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

[nota]

Originally Posted by stomachmonkey

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

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

[nota]

Originally Posted by dad911

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

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

[stomachmonkey]

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.

[nota]

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

[nota]

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

[nota]

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

[dad911]

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.

[stomachmonkey]

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

[nota]

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

[nota]

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

[nota]

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 ?

[stomachmonkey]

I'll be back home later today.

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

[nota]

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

[stomachmonkey]

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.



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.



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.

[nota]

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

[nota]

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