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Model A1418 / Late 2013 / 2.7 & 2.9 GHz Core i5 or 3.1 GHz Core i7 Processor

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iMac 2638 21.5" display not working after HDD changed

Hello all

RE; iMac late 2013 , 2.7Ghz, 21.5” A1418 , 2638

Having dismantled the main screen (as per ifixit tutorial) to get to the hard drive and then reassembled.

Reset the SMC (power off, unplugged at wall, hold down power button 30 secs)

Reset the PRAM (machine chimes, and resets and chimes ok)

Noticed there are four green LEDs on the logic board. one lights when plugged in. The other two light when powered on. however the fourth LED doesnt light up…

The internal display cable is seated properly at both ends. All other cables correctly seated too.

The machine worked great until had to remove and change internal HDD.

Any ideas what it may be ?

Unable to connect to an external monitor to check if display shows.

I have a 2011 MacBook Pro 17’ with thunderbolt port , is there is anyway I could connect the iMac to the MacBook Pro to check display?

Any ideas would be appreciated.

Thanks for reading

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Answer this question I have this problem too

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2 Answers

My input on this question is that you may have damaged one of the display cables (as they are VERY delicate) or the connector on the logic board has been damaged.

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Tried a couple of alternative display cables. Connectors on the logic board look good. However, still only 3 LED lights lit on board.

Checked board, all components look ok.



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Update . managed to find and run ASD 3S157 (OS +EFI) whilst connected to an external TV.

Ran the ‘Sensors’ test alone and the ‘SMC’ test alone as these are the two areas which flagged up errors.

EFI test results showed 2 errors

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OS test results showed 13 sensor errors in total

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With the 2 options (sensors + smc) unchecked. All other tests including , memory , processor and video for example passed.

So from my understanding, the SMC chip monitors all sensors on the logic board, which explains immediate error detection at the start of the EFI + OS tests. And the stand alone ‘sensor’ test revealed the extent of the sensor errors , around 13.

The iMac was assembled , faulty LCD all connected etc at the time of the test.

From my understanding, can one faulty sensor on the main logic board create other sensors to be faulty? Or are they all monitored individually by the SMC?

Logic board or LCD display at fault ir both?

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Bz8B1 will be eternally grateful.
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