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IMac 27 2009 Switching off during boot up

F

FatAlan

macrumors newbie
Original poster
Jan 23, 2018
11
1
Hi all,

Nothing worse that a "Hi, im new here but could somebody help me" post ill admit. I'm an active member on many forums but as macs are a renewed interest for me this is the first post on here. Sorry.

I have a 2009 27 inch mac that has been great for many years. Suddenly on New Years Eve it broke. Not normally a big issue but as I was intending on streaming music from it and it suddenly didnt work it could have chose its downtime better.

When I switch it one it chimes once, the screen back-light comes on and then it switches off. I am guessing at something overheating on startup but I dont know if macs have this sort of thing. I used to work as a technician on PC's (probably about 15 years ago though) and this was relatively common if the thermal paste broke down. Obviously this is 9 years old so this could be the case but I just wanted to check if there was anything else that could make a mac act like this.

Would the machine start if the problem related to the PSU and is the switch on the rear a momentary switch that I could jump on the motherboard to test the switch.

Again, apologies for a first post of this type - Im just lost in a whole new world of mac breakdowns (I guess testament to the original build quality I guess)
 
Hello there, welcome aboard.

It could be a few things, but at least you get a chime on startup. That's a good sign. It could be something like the backlight inverter has failed.
Apple 27" iMac A1312 LED Backlight Inverter Board 2009, 2010, 2011 661-5980

If you have some experience, you could replace it yourself. Watch a few 'how to's' first though.

The problem is that if this isn't the cause, you might end up spending a quite a bit to track down the cause.

Best of luck.
 
Thanks Razzerman.. I appreciate the response. I have just removed the screen (slowly and delicately) and I think I may have a couple of problems. There is a burning smell (not the most technical system test I will admit) so I am looking for something damaged with a magnifying class across the boards after I have done the LED tests and checked from the little test circuit on the motherboard. I have to say its a clever piece of design in here! Plenty dusty though. That probably hasn't helped :)

So -
Job 1 - clean
Job 2 - Check little LED's
Job 3 - use logic board test points
Job 4 - slowly investigate for anything obvious

Fun, fun, fun!
 
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Hehe, yeah, always plenty of dust in the old iMacs. Looks like you're on a voyage of imac discovery - enjoy the ride :)
 
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If burning smell could be PSU?

We hade replace a few PSUs here at work on 2006 white and 2008/9 silver iMacs.
 
elf69 said:
If burning smell could be PSU?

We had replace a few PSUs here at work on 2006 white and 2008/9 silver iMacs.
Click to expand...

Thanks for the input elf69.

I'm starting to suspect some kind of PSU issue. I have found if I remove all of the memory it will stay powered up with a beep every 10 seconds (ish). Upon replacing the memory it again fails to boot. Just starts up and then switches off again.

Im guessing that the mac runs through a series of tests before booting and finding no memory will essentially halt the boot process. At the point where the mac switches off I'd suspect the hdd should start spinning up. I cannot hear it so Im going to disconnect it and see what happens. To eliminate problems with the on/off switch I am currently jumping the on/off pin on the motherboard. My only concern is that I going through a process of checks for a generic PC.

On an unrelated topic - Is that a Riley I see? :)

What an exciting project I have opened up!

Alan
 
yes it has a self test thing on boot, much like P.O.S.T. in windows based machines.

PSUs can be had for these machines ebay and thebookyard would be my first ports to call.

My avatar is a 1972 Austin 1300.Vanden Plas Princess, one of my projects.
I do own a 1969 Riley Elf too, also project.

I love to tinker inside my iMac.
Soon to fit SSD (240GB) and cpu upgrade 2.0 to 2.8GHz.
 
elf69 said:
yes it has a self test thing on boot, much like P.O.S.T. in windows based machines.

PSUs can be had for these machines ebay and thebookyard would be my first ports to call.

My avatar is a 1972 Austin 1300.Vanden Plas Princess, one of my projects.
I do own a 1969 Riley Elf too, also project.

I love to tinker inside my iMac.
Soon to fit SSD (240GB) and cpu upgrade 2.0 to 2.8GHz.
Click to expand...

Great collection there! My last venture into older British cars saw me in a Rover P6 V8. Its been a long time since Ive seen a Vanden Plas from that era. I do miss the old rovers sometimes (except at fuel stops I guess). Currently in a 20 year old saab 9-3.

Anyway, Ive stripped down to the motherboard. Found a few things I don't like. It looks like somebody has soldered something (I got this 2 or 3 years old) poorly but it seems to have been working ever since so I wont touch that. The on/off switch was not particularly great so I may as well replace that while im in here. Everything is chocked to the brim with dust.

I think I'm going to get thermal paste and clean up the GPU and CPU incase its just an intel cpu based "protection switch off" that I have encountered on PCs .

The PSU is about to get removed for a good check over too. This is fun.
 
for paste I use arctic MX, got some MX2 but they do 3 or 4 now.

Mine pretty dusty inside but gonna wait until do CPU to clean it fully as got take mono out for that anyway.

I love classic cars, always have.
the elf was birthday gift from parents!
The vandal plas after getting it home turns out to be one of only 3 built.
It has strange trim combo which makes it rare.

and being a 1300 is good on fuel
 
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Well.. its looking to be power related. It will start up and not switch off if I disconnect the hdd. As soon as I plug the HDD back in it fails to stay switched on.

So.. Looks like a new power supply will be sought. Im presuming it has to be from a 2009 27 iMac and I cannot hack and splice something in from another iMac model?

Its annoying really... upon searching for parts it looks like the poor thing is worth more in bits. Ive never really looked for parts for it. I think the memory was purchased a few years back and nothing else has been problematic. If I break it I will only have to buy another so it all leads to expenditure ultimately.
 
Its a 27 inch. Ive got 4 leds on after putting the screen back in so its a good bet that the PSU is the next step. The screen back-lights okay but there's nothing on it at all. As soon as I plug the HDD back in its switching off again. This has been a fascinating learning experience I must say :)

I'm a little nervous that I have nothing coming up on the LCD I will be honest but at least its switching on and staying on. The temperature sensor wires that wind around the insides of these machines are something to fear. hanks

Looks like i have to wait till pay-day. Its still a lot cheaper than a replacement machine!

Thanks for the heads up on bookyard.com - I never knew it existed :)

Cheers,

Alan
 
the 27 inch has few models m8

the i5 model might have bigger psu.

Have you tried external screen?
Also plug the HDD into a usb and see if boot from it.
could be just sata power issue?
 
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