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Model A1419 / EMC 3070 / Mid 2017 / 3.4, 3.5 or 3.8 GHz Core i5 or 4.2 GHz Core i7 Kaby Lake Processor (ID iMac18,3) / Retina 5K display. Refer to the older iMac Intel 27" Retina 5K Display (Late 2014 & 2015) guides as the system is very similar.

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Fan speed too low after replacing it.

My fan stopped working, so I ordered one from ifixit. After replacing it, the fan speed idles around 450~490rpm, and won't go above 500 even when the CPU temp reaches above 90celsius. I've installed Macs Fan Control to try and manually adjust the fan speed to no avail. Is the fan I received from ifixit faulty, or is there something else I can try?

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This could be a faulty fan, but I would take a look at the Troubleshooting Problems After a Repair wiki page, just to cover all your bases. If the old fan wasn’t working at all, it could be the issue is still with something else, but I would make sure all the connections are sound. It could just be something as simple as it isn’t fully connected.

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If forcing the fan doesn’t alter the speed, then the tachometer logic is not working properly. This tends to be a logic board issue. This will need reviewing of the schematics and board-view drawings measuring the voltages as well as inspecting the board for damage burnt components as well as corrosion damage.

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Hello Dan, thanks for your reply.

The day after I posted the initial question, the fan seemed to run at the normal speed (above 1200rpm), but since then it has returned to anywhere between 250~400rpm. I'm assuming it's probably a logic board issue as you've described.

I'm not really a tech person - I'm ok with disassembling and reassembling things, but not familiar with measuring voltages or swapping out chips, etc. Would you say my only option then would be to change the entire logic board?

Thank you in advance for your help!

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Kyu Hwang will be eternally grateful.
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