iMac slow after screen replacement, fans up
I replaced my screen after it broke, and now the fans go crazy and the machine is slow, and the mouse response is sluggish (my mouse feels drunk).
Model A1418 / Late 2013 / 2.7 & 2.9 GHz Core i5 or 3.1 GHz Core i7 Processor
This model of screen has a small thermal sensor with cable that is attached on the screen.
If you turn the old screen, look at the back/top. You will see a small board that has two cables plugged in. One of those usually connects to the main mother board (the larger cable), the other one (the narrower and shorter cable) goes to a tiny piece of circuitry which is actually the thermal sensor.
With that sensor unplugged (if you left it on the old screen and did not transfer it to the new screen), the fans will ramp up to the max speed, and the iMac will interpret it as something is overheating and will consequently slow down. You can double check this by installing a temperature monitor like Aidan suggested. It should say that the LCD thermal sensor is bad/missing or giving a high temp signal.
hi, iMacs normally have a thermal sensor either attched to the screen or built in (possibly not 100% sure about built in) but you probably forgot to reattach the thermal sensor to the logic board (Replacment screen may not have come with thermal sensor) look at ols scren for any other cables other than display cabe :)