fixing an apple computer power supply

[stomachmonkey]

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.

[nota]

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

[stomachmonkey]

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.

[mrrolleyes]

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.

[stomachmonkey]

Originally Posted by mrrolleyes

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?

[mrrolleyes]

Originally Posted by stomachmonkey

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.

[nota]

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

[stomachmonkey]

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.

[stomachmonkey]

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