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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

Posted on Mar 9, 2018 10:26 AM

Best reply

den.thed

Level 9

77,158 points

Posted on Mar 9, 2018 2:35 PM

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

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iMac Screen goes black (ODD temp sensor faulty?)

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