iMac slow after replacing display

[romeyn]

I have a 21.5 inch late-2012 iMac 13,1. When I acquired it it had a bad hard drive. I have replaced the HDD with an SSD from OWC. I also replaced the display, because I dropped the original and it cracked (just the glass, not the display itself. When I put it all back together (I haven't adhered the new screen yet, it's just resting in place) the computer ran extremely slowly. kernel_task using 300% or more of the processor at times. I downloaded something called HWmonitor that shows all the sensors and fans--there are two "Ambient" sensors, one of which registers about 250 degrees Celsius!! And the fan runs top speed. I have performed numerous SMC and PRAM/NVRAM resets to no avail.

This evening I removed the SSD and hooked it up externally/USB. The computer is still slow. Then, on a lark, I put the old cracked display back on. The computer is fast again! (Though that Ambient temperature is still over 200 degrees, which is odd.)

I am at a loss to explain this. Where can I get more details about that sensor reading? I'm aware that some Macs of this era had HD temp sensors, but my research suggests that this is not one of them. And what about a DISPLAY would cause the computer to slow down?

 

[harryb2448]

G'day and welcome to the forums.

I think the fall has critically injured the thing. No the 2012 21.5" iMac does not have heat sensor cables.

It is amazing years since seen reports of dropped iMacs and a cuple in one day.

 

[romeyn]

Oh, I never dropped the computer. Just the original display, while it was off the computer. It fell over (I should have laid it flat and not leaned it against something unstable).

 

[harryb2448]

Sorry misunderstood slightly, which is not unusual for me at my age!

Running via USB, even USB3 will always be like treacle compared to the internal fitting of an SSD running at 6Gbps. Set up with the new drive internal and new screen, and boot up. Go into Utilities > Activity Monitor and see if anything is hogging things. Also, the sticky kit, which you can get from eBay for about ten bucks, may have something to do with things when you reconnect all cables. Unless the cables are fitted correctly and firmly that Jumbo roaring is typical.

 

[pigoo3]

You're "sharp s a tack" Harry. No worries!

- Nick

 

[romeyn]

UPDATE: Through trial and error I determined that there was something inherently faulty about the replacement display I received. When it was present, the LCD temperature sensor read HOT and the computer was dog slow with fans running. If I put the old, cracked display back on, everything was fine. I transplanted the sensor from the old display to the new one with the same result--slow when new display present. Diagnosis: faulty display. The vendor has replaced it. Last night I installed it. LCD sensor reads normal and computer is blazing fast.

Although an "Ambient Temperature" sensor reads about 249 degrees C!! And yet the fans are behaving normally. I have looked and looked and can't find a diagram of where these sensors are located. Any advice on that?

 

[chscag]

Although an "Ambient Temperature" sensor reads about 249 degrees C!! And yet the fans are behaving normally. I have looked and looked and can't find a diagram of where these sensors are located. Any advice on that?

Have you checked the break out diagrams at www.ifixit.com?