Weird problem iMac mid 2011 21.5

[SCREAM ESP]

Hello there

A friend' iMac has stopped working, does not power on. It is iMac mid 2011 i5.
He brought it home for testing, and I found only LED #1 lights up when plugged. Power button does not power up the machine.

-Power button works. Measured with a tester, both pins are shorten when button is pressed
-PSU seems fine, it has 4v on pin #2 and 12v on pin #4
-I have a spare GPU, installed on computer and problem is still there. So no GPU failure either

So I runned out of options. Does anybody know where/what to check next?

(Please excuse my english)

 

[MandiMac]

Maybe the motherboard itself is dead?

 

[SCREAM ESP]

Very likely, yes. Still, maybe could be something else, or it could be some SMD component that can be replaced

Thanks for your reply!

 

[MandiMac]

If it won't power up, I don't think you can do a VRAM reset and the likes. Does it recognise any startup shortcut commands?

 

[DeltaMac]

Have you tried an SMC reset?
If that doesn't help, then I suspect that the PS is bad. (Even if you measure what appears to be good voltage, the PS might not be able to come under load (and supply power to the rest of the system)

 

[SCREAM ESP]

Nothing at all, despite 1st led is on when plugged. I did SMC Reset, but it doesn't come to life

Also, I forgot to mention that I tried with and without memory SIMMs installed

 

[DeltaMac]

Your first choice: Replace the power supply.

 

[SCREAM ESP]

Don't have any available. Do you think that's where the problem is? I've measured pin 2 and 4 and voltage is correct

Thanks for your replay!

 

[DeltaMac]

Don't have any available. Do you think that's where the problem is? I've measured pin 2 and 4 and voltage is correct

Thanks for your replay!

If you want to repair the iMac, then you would need to try a few things. Some of those you have already tried.
As I said, if the power supply won't supply power under load, then measuring some connected voltage doesn't mean very much, other than you have determined that there's voltage there. The power supply has to come under load during boot, and if that won't work, then --- no boot.
I don't know for certain that the power supply is the problem, but it's your next step. (Get it from a company that will allow you to return the part if it doesn't fix your issue.)
Apple's part number for that power supply is 661-5299, which should help you be certain that you get the correct part.

 

[SCREAM ESP]

Thanks for your tips DeltaMac, it is very useful

I've found a PSU from 2010 iMac (i3) which looks pretty much the same component. I will check P/N to verify whether it's the same or not. I have some work to finish today...

In case it's not suitable for 2011 model, then he will have a problem. There's nothing here I can buy and return in case it's ok. In that case I think is better for him to save money for another Mac

Thank you!

 

[DeltaMac]

...
I've found a PSU from 2010 iMac (i3) which looks pretty much the same component. I will check P/N to verify whether it's the same or not. I have some work to finish today...

In case it's not suitable for 2011 model, then he will have a problem. There's nothing here I can buy and return in case it's ok. In that case I think is better for him to save money for another Mac
...

2009-2011 21.5-inch iMacs all use the same power supply, so you will be OK with a 2010 part.
(The part number that might be on the power supply label is the manufacturer's part number, so will be different. If the power supply came from a 2010 21.5 iMac, then it will be the correct part.)

 

[SCREAM ESP]

2009-2011 21.5-inch iMacs all use the same power supply, so you will be OK with a 2010 part.
(The part number that might be on the power supply label is the manufacturer's part number, so will be different. If the power supply came from a 2010 21.5 iMac, then it will be the correct part.)

Great! So I'll check it out tomorrow and see what happens. I'll report

 

[SCREAM ESP]

Bad luck. Tried a knowed working power supply, and still it does not power up

 

[DeltaMac]

If you still get no response from the system (no fans, no boot chime, no video, etc) -- Apple's service manual says to try replacing the DC power cable (connects the power supply to the logic board). You might try that next, but my feeling is that the power circuitry on the logic board has failed somehow, and you will ultimately need to replace the logic board anyway.

 

[SCREAM ESP]

Well, It's something I could try. I'm into mobo problem though.

He switched computer off at night, the next day it did not go on.