iMac 21.5'' 2011 - won't boot anymore

[mariozankl]

Hello everybody,

It's about my mother's iMac that I gave her many years ago. It's a 2011 model with 21.5 inches.

The iMac suddenly turned off while surfing and couldn't be turned on again. There is also no boot sound to be heard. The screen just stays black.

What I have already tested:

- Disconnected from the power for 15 minutes -> did not work.

- Reset the NVRAM with alt, cmd, P and R -> A boot sound is played every 10 seconds as long as i keep the buttons pressed. But still no image.

- I also opened the iMac. All 4 status LEDs light up after pressing the power button and the fans also rotate. So far everything is normal.

What else can i try?

 

[chscag]

That model has been plagued with GPU troubles: failed GPU or one that is failing. Not saying positively that's the problem, but it does sound like the GPU has failed.

If it has, I personally would not try repairing it. Not worth it for a machine that old. Might be time to get Mom a new or newer machine.

 

[mariozankl]

But with a defective GPU, the 3rd and 4th LEDs shouldn't light up, right? Or can it happen that the LEDs light up anyway?

 

[chscag]

But with a defective GPU, the 3rd and 4th LEDs shouldn't light up, right? Or can it happen that the LEDs light up anyway?

I can't answer that as I'm not familiar with those LEDs. However, the way the iMac is acting, a GPU failure is a possibility. I thought maybe the HDD had failed but no boot chime almost always indicates a serious hardware failure and the machine would chime even if the HDD was bad.

Could also be a bad logic board, but again that's just a supposition.

 

[USB3foriMac]

But with a defective GPU, the 3rd and 4th LEDs shouldn't light up, right? Or can it happen that the LEDs light up anyway?

Probably depends on how the GPU fails...
So to confirm: you have no boot chime (or do you?)
Hold the option key when booting, check whether this brings up the boot menu. If yes, maybe the HDD faulty. Try a boot stick (e.g. Linux Mint or High Sierra).
Take the thing apart (30 min), take out the GPU and bake it. Read up on "GPU bake". My suggestion is 6 min at 200 degC.
Then reassemble. Problem solved (for a while). Can be repeated after months/years.

 

[mdgm]

Something else you can easily check is replacing the coin battery (I think it is a BR2032). After 9 years it wouldn't be that surprising if that is dead and needs replacing.

 

[mariozankl]

Today I completely disassembled the iMac. CPU and GPU coolers removed, graphics card baked for 8 minutes at 200°C and reassembled with fresh thermal paste and pads. I also changed the battery. When assembling it I noticed that one of the two RAM bars was not right in the slot. Now the iMac boots again (boot sound can be heard) but I still have no image.

But now, if I shine the flashlight on the screen, I can see something. So I checked out the inverter board. And then I saw that one of the coils was missing. Looks like it got so hot that the solder has softened. The coil was at the bottom of the case. I soldered the coil back on, but it didn't work. Looks like the inverter board is broken. I have now bought one on ebay. That should arrive after the holidays. I hope this will get the iMac working again.

 

[chscag]

Nice bit of troubleshooting. Let us know when the new inverter board arrives.

 

[mariozankl]

After 6 weeks of waiting I finally got the inverter board. The iMac is now working again. Thank you for your help.

 

[Fishrrman]

Nice work getting it running again.

But... I would consider its days ahead to be "numbered".

Time to get a good backup system in place if that matters to your mom.

You also ought to start to "think about a replacement" before too much longer...