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Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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iMac 27-Inch (Mid-2011) A1312: dodgy GPU, inverter and fans gone hyper

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Hello,

I’ve been wondering how much longer my iMac 27-Inch "Core i5" 2.7 (Mid-2011) A1312 can keep going. Then the other day the screen went black. First time it’s played up.

Looked it up: seems GPU was a recall issue so good that I got 9 years out of it.

Did the shine torch thing – all was black.

Did the PRAM and something similar. No change.

Hooked up a spare Acer display in the Thunderbolt – all good so I can carry on working.

Q1. If Acer works does that mean the Mac’s GPU was fine all along and it was inverter board? Or does the Acer have its own GPU?

Called a repairman. He replaced the GPU with presumably a used unit and at the same time hoovered out a shed-load of dust.

(The iMac casing did get quite hot – much cooler now with dead screen. I used to hoover the vents periodically but never occurred to dismantle and clean the insides.)

Repairman restarted: still no screen but now all the fans came on flat out.

He checked for dislodged temp sensors and connections. (I think he had to lift the logic board to get the old GPU out. Did not watch it all).

He could not find any so suspected a blown inverter board and, with now GPU fixed, explained the dead inverter was setting the fans off. Could be wrong, but this sounded more like he was looking for excuses caused by careless hoovering or reassembly.

The fan issue was hacked by downloading TG Pro Manual fan controller as clearly having the fans flat out was not an option. If the iMac goes to Sleep the fans kick off again.

Q2. Would a blown inverter set the fans off?

One thing I notice on the TG Pro menu is that various GPU components read warm.

GPU Diode 45

GPU Heatsink 42

GPU PECI 31

I don’t know what any of these things are but does that mean GPU is working OK and the fault is downstream?

Fyi the 4 CPUs are low 30s °C and the hottest thing on the menu is the Platform Controller Hub Die (47).

The coldest is LCD Monitor Proximity 19° C (room temp?) – or the Case: 28°C.

Also, is this menu of some 2 dozen item temperatures a list of heat sensors?

And if one was not working would it not read oddly low?

Thanks for any ideas.

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If the external display was showing a working image that removes the GPU, so I don’t understand why the repair person altered it as its not your problem!

A dead inverter board would still have shown you an image on the LCD panel using the flashlight to see the faint image. So clearly that failed! So that tells us the issue is not the inverter. If you where in a dark room you would have seen a grey glow from the backlight which would have also proved the inverter was OK!

So that removes the two parts you had suspected! There is only one other part here! The display its self! Time to fix the real failure! Hopefully the other fixes don’t do you in.

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Thanks Dan. So it looks like the Mac repairman stiffed me (and charged the highest possible price for the GPU too ).

I should have checked here first but assumed the lown GPU was obvious.

And the fans? Is that down to a dislodged sensor somewhere?

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Fan's running hard is SMC not getting a sensor input. Likely, the display was not connected back properly or one of the other sensors got damaged in the repair process.

Sorry you found a hack! At least see if you can get your money back!

Talk with your local Better Business Bureau (BBB) or State Consumer Protection in any case to file a report - Sorry ;-{

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Thanks again Dan. While looking for absolute confirmation of burned-out LCD before buying a used one, I came across a similar GPU issue from 2016 by Ben

videocard or LCD screen dead?

He mentioned no built-in Monitor ('Displays') appears in his System Prefs.

'Displays' appear on mine and I can toggle between built-in and the Acer, fwiw.

And on my About... > System Report it registers both displays (as below).

Can that still mean the built-in LCD is finished?

Displays:

iMac:

Display Type: LCD

Resolution: 2560 x 1440

Pixel Depth: 32-Bit Color (ARGB8888)

Main Display: Yes

Mirror: On

Mirror Status: Master Mirror

Online: Yes

Built-In: Yes

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Yep! You've found another way to prove the issue is with in the display panel as you can see the GPU logic which then sees the display unlike Ben who couldn't.

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Thanks again for helping me get to the bottom of it.

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Chris S zal eeuwig dankbaar zijn.
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