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Question: iMac Screen goes black (ODD temp sensor faulty?)

I have an old iMac 2390 (intel, unibody, 8-ish years old) my dad upgraded from and I'm trying to turn it into a computer for my mom, but the screen goes black after a minute or so and I have to restart it to get it to work again--but just for a few minutes. Apple support told him to buy a new mac or spend $1400 on a new display and gpu, so he got a new mac. I'm trying to fix this myself and I've taken it apart twice; once to clean out the dust, and again because a fan was running too loud. And it actually did work when the fan was running fast. I think this is because I didn't plug the ODD temp sensor in properly the first time. I'm wondering, could a faulty sensor for the ODD be causing the mac to turn the screen off? Has anyone else experienced this? Is there a way to disable the sensor via command line or software preferences or do I need a new one? Also where could I get one?


Sorry, long question. I'm a PC guy and not used to the hardware of apple computers, so I need a little help. I don't know how to dig far into the software either. Thanks for reading this, and thanks if you have any advice.

iMac, iMac 2390

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Mar 9, 2018 12:36 PM in response to Peter_R_Science_Wizard In response to Peter_R_Science_Wizard

I would recommend taking the computer to a third party AASP rather than trying to do-it-yourself. You have stated yourself you aren't familiar with Macs, I'd recommend taking it to someone that knows what they are doing. While I know that isn't what you wanted to hear it likely going to save you time, effort and maybe money in the long run.

Mar 9, 2018 12:36 PM

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Mar 9, 2018 12:59 PM in response to Peter_R_Science_Wizard In response to Peter_R_Science_Wizard

Sounds like two completely unrelated issues to me.


On a good note: if the OOD fan is working properly after reconnecting the sensor wire, then it sounds like you have recovered from that issue.


On a more realistic note: the all-in-one units (some models in particular) are notorious for running hot which causes premature GPU and Display failures.


If the GPU is it not completely toasted, then there are a couple of things that can be done to get a little more life out of the unit.

1. It sounds like you have completed the first, which is cleaning out the dust to ensure proper cooling.

2. Is checking the heat sink for cracks and reapplying thermal past to the GPU.


Sadly if it needs a new GPU. (they are hard to come by and not cheap)


I'm not sure if you have a 2010 or 2011 model?

But there are some great DIYs that cover re-pasting and GPU replacement at > iMac Intel Repair - iFixit

Also there a numerous Suppliers that may have re-conditioned or new GPUs, once you have established the GPU's part # that year model.

Mar 9, 2018 12:59 PM

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Mar 9, 2018 1:29 PM in response to rkaufmann87 In response to rkaufmann87

I would but I would rather not spend the money, repair centres I've talked to either say that the might be able to help, or that they can't service the mac anymore. Those that do say they can help give me a pretty high price tag. And, not to be arrogant, but as complex as this iMac is I've dealt with worse; you should see how complex Archos made their media tablets. I mostly meant that I'm not familiar with macs in that they have some features I haven't encountered in pcs, and the software side of things is something I don't know much about.

Mar 9, 2018 1:29 PM

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Mar 9, 2018 1:39 PM in response to den.thed In response to den.thed

Oh, this is a mid-2010, a1312, 2390, imac 11,3, MC511xx/A, at least according to wikipedia for which I've matched the specs to this model. For the GPU it is fine, its an HD 5750 with 1GB G-RAM. And, it can run an external display normally. Though before the issue started my little brother started trying to game on this mac, which it didn't take too well. And as I said while the ODD fan was running at max speed it was working just like normal. I replugged that cable in and the fan spun down but the display issue started again.


I'm going to try taking it apart again to try reseating the display and temperature probe cables and see if that works. But first, do you know a way to monitor just what the mac is detecting or doing? In windows I have a whole bunch of monitors I can use to see temperatures, fan speeds, failures, and errors. Is there a way to track what the mac is doing? Like, while having an external monitor connected check to see if the mac is detecting an overheat or other issue and shutting down the display? Or see if a sensor is reading properly?


Thanks you.

Mar 9, 2018 1:39 PM

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Mar 9, 2018 2:35 PM in response to Peter_R_Science_Wizard In response to Peter_R_Science_Wizard

The Apple Hardware Test can detect faulty sensors, drives and other hardware problems, but it has never been able to diagnose graphics or display issues.

How to use Apple Hardware Test on your Mac - Apple Support


There are several good third party utilities out their that are able to access the iMac's internal sensor array.

https://www.bresink.com/osx/TemperatureMonitor.html

iStat Menus on Setapp | An advanced system monitor for your menubar


Personally I use MacFanControl for monitoring and controlling the Fan Speeds.

https://www.crystalidea.com/macs-fan-control


FWIW, faulty or disconnected temp. sensors cause a problem for the System Management Controller which causes the fan in that area of the system to ramp up out of control. It does not directly cause other hardware issues. In addition you will also find that if you kick up the CPU fan using MacFanControl. It will also help keep the GPU cooler, because both the CPU and GPU heat sinks are cooled by the same fan.


However in most cases, it is just a bandage once the GPU has been overheated and damaged.


Edit: for a GPU, google part # 661-5578

Mar 9, 2018 2:35 PM

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Mar 9, 2018 6:09 PM in response to den.thed In response to den.thed

Thanks. I'm going to reserve getting a new GPU as my last resort. I just want to see what is going on with the mac. Also check to see if the ODD temperature sensor, or maybe the lcd sensor is faulty. I know you all say it's probably the GPU and I'd agree if it weren't for being able to use an external monitor just fine. And I still think something else weird may be going on, seeing as everything worked fine when the ODD sensor wasn't plugged in properly and the fan was maxed. If nothing I try works I'll try a new GPU--new thermal paste on the old one first though, if that'd fix it.


Thanks Again.

Mar 9, 2018 6:09 PM

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Mar 9, 2018 8:59 PM in response to Peter_R_Science_Wizard In response to Peter_R_Science_Wizard

Peter_R_Science_Wizard wrote:


I know you all say it's probably the GPU and I'd agree if it weren't for being able to use an external monitor just fine.

Good point! The other component that could cause the display to black out is the backlight inverter or a bad cable. One way to check for that, is to hold a flashlight up to the display when it has black-out and look to see if there is an image on the display.


And I still think something else weird may be going on,

Well at least now, your starting to understand why the AASPs estimate was $1400. Cause it sounds like they were covering there back-side incase in needed a GPU, an Inverter Board, Display Cables and Display.


Thanks Again.

No problem, you're welcome!


Hopefully I have helped enough, for you to either get it going again or to just let go without wasting a wad of cash trying to fix it.

Mar 9, 2018 8:59 PM

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Question: iMac Screen goes black (ODD temp sensor faulty?)