Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor

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CPU i5 3,1GHZ Throttled to 1.6GHZ

So i tried to replace my i5 2400 3,1 GHZ CPU with a i7 3770 it did not work. I reinstalled the i5 2400 and everything worked normal except the Fans for ODD and CPU. Well i thought no problem i will regulate it with software. But then i experienced a big drop of perfomance in OBS and Logic. I installed intel Power Gadget and noticed the CPU Frequency is locked to 1.6GHZ.

The Apple Hardware-Test says: 4SNS/1/C0000008: TLOp--124

I searched in the Web and found that it must be a Temperature Sensor connected to the LCD.

1. SMC PRAM VRAM Reset

2. I ordered a new LCD Tempsensor - replaced it but nothing changed.

3. I ordered a new V-SYNC /TempSens Cable (connected to the LED Backlightboard) nothing changed.

4. I ordered a new LCD Data Cable - nothing changed.

5. I ordered a new Logic Board + CPU - nothing changed.

So these are the steps I did until now and I don't know what to do now...

The only thing left i could imagine would be the LED-Backlightboard maybe reinstall OS or could be something wrong with the EFI, Powermangament I dont know.. Maybe someone experienced the same issue or knows how to repair it.

Everything else except Fans going wild and CPU is throttled works well.

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EDIT: (This Programm is called HW-Monitor and is the only one that shows me 128° on LCD)

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EDIT:

So i was away for like 2 hours and the imac was in Sleepmode when i came back i saw this:

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Sadly it went back to 1.6GHZ after a short period of time.

EDIT:

So its definely reproducable. I have to put the iMac in Sleepmode for 20-30secs and when i wake it up the CPU runs normal ant turns to 1.6GHZ after 10secs. What the !&&*...

Maybe another hint. When I turn on Sleepmode the fans are stopping. NOW when i wake up the MAC TGPro is showing my some N/A Temperatures:

GPU DIODE

Platform Controller Hub DIe

As soon as these both Temperatures are availabe the Fans power up and the CPU gets throttled.

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EDIT:

Tried to reinstall OS X did not help..

EDIT:

Tried to run the iMac without the LCD on a second Monitor did not work.

When i opened the iMac i noticed strange "glue" on the poweradapter:

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Also i run a SystemDiagnosis which gave me the same error as the AHT:

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This week i will probably bring it to an Authorized Apple Reseller and hope the can help me.

Answered! View the answer I have this problem too

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Did you change the hard drive while you were at it?

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No i ordered it with an SSD and HDD, i had to change the SSD like 3 years ago but everything worked fine. HDD is still the same.

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Well but of course i had to disconnect the HDD and SDD to change the CPU / Logicboard

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Could it be a faulty connector on the LED-Backlightboard ?

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Tell me about the new SSD you installed.

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Chosen Solution

I was able to fix the problem. Switched the LED-Backlightboard and it worked.. I think the connector to the LCD V-Sync/temp - cable was faulty. Thanks for everyone considering solutions!

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So everyone with the TLOp Error should consider to check the V-Sync / Temp cable and the LED-Backlightboard! :)

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Can't say for variance, but it sounds like some temp sensor for the CPU is going crazy. The high fan speed and throttling could be because of thermal reasons (or so it thinks). Try reseating the CPU and see if that helps. Also, tell your temps please.

EDIT: did you replace the thermal paste?

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Just watch the pictures everything is there ;) .

The thing is I switched the Logic Board + CPU. So the problem can't be the Logic Board or CPU.

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I replaced the thermal paste when i switched to the i7 3770 and again when i switched to the i5 2400. But thats the old logicboard. The new Logic Board came with the CPU attached.

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Valentino Vian will be eternally grateful.
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