2012 27" iMac runs slow after replacing screen

Question

iMac Intel 27" EMC 2546

Model A1419 / Late 2012 / 2.9 & 3.2 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac13,2

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David Joyce @macdaddyo

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iCare4Macs

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crwdns2931729:0crwdne2931729:0: Nhl 8, 2017

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2012 27" iMac runs slow after replacing screen

Has anyone encountered the replacement of a screen impacting the speed of the machine? It doesn't make sense to me, but the only thing done was the screen replacement, and now the machine runs incredibly slow. The machine ran fine with the cracked screen, and not so much with the new one.

I bought it from a reputable place, and they are willing to ship out a replacement screen, but I'd rather not do that, unless the screen could impact the performance.

Thanks in advance for any thoughts.

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At the risk of looking foolish, but willing to admit in hopes to keep someone else from having my same issue. Turns out, the sensor that both Anthony and Dan mentioned was not included with the replacement screen. Nor was this mentioned by the distributor. When I pulled the old screen out, there it was, in plain sight. Duh... I removed it, put it on the replacement screen, and the machine was back up to speed.

I won't make this mistake again, but sure would be helpful if this were pointed out either when purchasing or when I opened the box. Cost me a lot of time, and more importantly my client a lot of frustration, but in the end, he's happy and I learned a valuable lesson.

Thanks to both Dan and Anthony for guiding me, and for iFixIt for having a helpful resource in this board, one that appears to be Flame-Free.

crwdns2934271:0Nhl 15, 2017crwdnd2934271:0 David Joyce crwdne2934271:0

Thank you for posting this David Joyce.

You just saved me, and my client, a lot of time.

crwdns2934271:0Maw 12, 2020crwdnd2934271:0 hustonb crwdne2934271:0

Can I know how the sensor look like ? Because I face the same problem of extremely slow after change to new lcd . Thanks for reply

crwdns2934271:0Mha 12, 2024crwdnd2934271:0 FAM crwdne2934271:0

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At the risk of looking foolish, but willing to admit in hopes to keep someone else from having my same issue. Turns out, the sensor that both Anthony and Dan mentioned was not included with the replacement screen. Nor was this mentioned by the distributor. When I pulled the old screen out, there it was, in plain sight. Duh... I removed it, put it on the replacement screen, and the machine was back up to speed.

I won't make this mistake again, but sure would be helpful if this were pointed out either when purchasing or when I opened the box. Cost me a lot of time, and more importantly my client a lot of frustration, but in the end, he's happy and I learned a valuable lesson.

Thanks to both Dan and Anthony for guiding me, and for iFixIt for having a helpful resource in this board, one that appears to be Flame-Free. — David Joyce
Thank you for posting this David Joyce.

You just saved me, and my client, a lot of time. — hustonb
Can I know how the sensor look like ? Because I face the same problem of extremely slow after change to new lcd . Thanks for reply — FAM

score 3 · Answer 1 · 2017-10-08T15:35:13-07:00

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Dan @danj

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Self employed contract worker

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crwdns2931729:0crwdne2931729:0: Nhl 8, 2017

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The screen has a thermal sensor which if not responding SMC will go into Safe mode lowering the processors clocking. The easiest way to verify this is to use a good thermal sensor monitoring app like TG Pro.

Here's a snip from the schematic of the thermal sensors:

T-CON & LCD are both on the display assembly.

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Hi Dan -Thanks for this, it seems to point to the cause. I still have the origial cracked screen to look at, and see no additional connections that I might have missed. I assume that the thermal sensor communicates thru one of the two connectors. Is there anything I might have missed here before I request a replacement screen.

crwdns2934271:0Nhl 9, 2017crwdnd2934271:0 David Joyce crwdne2934271:0

Did you run TG Pro to verify? I would, and I would also make sure the cable connections were sound on both sides.

And yes, the connection is though the ribbon cable to the logic board.

crwdns2934271:0Nhl 9, 2017crwdnd2934271:0 Dan crwdne2934271:0

I have TG Pro running on the his machine, bought it last week, and none of the sensors showed any issues. However, I don't see one specifically mentioning the screen.

crwdns2934271:0Nhl 9, 2017crwdnd2934271:0 David Joyce crwdne2934271:0

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score 2 · Answer 2 · 2017-10-08T14:03:44-07:00

Anthony @anthonyj

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The Mac Studio

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I've had issues with the 2012 iMac LCD LVDS cable not being seated properly. If it's not seated 100% correctly it could impact your performance of the LCD. You could buy the LCD adhesive kit to try yourself but It's very annoying replacing the cables as it requires a lot of patience. We test our screens 3 times just to ensure we do not have to open the thing up again...

Was your hard drive touched at all? Run Smart Utility to test your drive. If it is failing that could also be an issue.

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Hi Anthony - Thanks for this. I did boot the machine several times, prior to closing it up. Found no visual screen issues, so proceeded with sealing it up. We had replaced the HD several months prior, and even with a non-Apple drive, it ran fine and quite. It was only when the new screen was put on, that the machine went wonky. Fan running wild, and machine slowed way down. I installed TG Pro to quite the fan, and don't see any sensor issues, but still it bogs down. HD tested fine with several tools. BTW - do you have a shop operation, or like me, only work onsite at client locations?

crwdns2934271:0Nhl 9, 2017crwdnd2934271:0 David Joyce crwdne2934271:0

Hello David, I run a shop in Venice CA and also do onsites. Dan is right about the SMC verifying the thermal condition and lower processor speeds. If you replaced the HDD you could consider an OWC thermal temp sensor just to make sure it's not that ( I do doubt it is that). I do have another theory... The LCD they replaced may not have came with a thermal sensor or the sensor may be damaged. When I buy LCDs for iMac retina displays I always have to replace the cable with the customer's. Maybe your cable was not installed or damaged in the removal process?

If you can open your imac look at picture on Step 21. Can you see the small cable to the right on the main 2? This cable may be your culprit.

iMac Intel 27" EMC 2546 Display Replacement

crwdns2934271:0Nhl 10, 2017crwdnd2934271:0 Anthony crwdne2934271:0

The screen I purchased, from a local Hollywood distributor, came with the cable on the left side of the image in step 21, but not the righthand one. That one I took from the clients original screen. Which one monitors the sensor on the screen? I agree, the OWC thermal temp sensor would be a good idea, although the machine ran fine for 3 months without it. All this started with the replacement screen. Good to know you have a shop location. I'll put you in my Contacts for clients on the westside in need of hardware repair.

crwdns2934271:0Nhl 10, 2017crwdnd2934271:0 David Joyce crwdne2934271:0

Thanks David! Are you in Hollywood? The cable you took from the client's original screen is the sensor most likely causing your issue, I would double check it for any damage or find a replacement. Beetstech has it for $18. I cant guarantee it will fix your issue but it's a good start.

crwdns2934271:0Nhl 11, 2017crwdnd2934271:0 Anthony crwdne2934271:0

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iMac Intel 27" EMC 2546

2012 27" iMac runs slow after replacing screen

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Update (10/09/2017)

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