Model A1418 / Late 2013 / 2.7 & 2.9 GHz Core i5 or 3.1 GHz Core i7 Processor

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Missing resistor, SMC and/or temperature sensor failure iMac late 2013

Hi all,

got some trouble with my imac late 2013, as the fan is running high all time although there is no (obvious) reason.

Well to make long things short, I ran the Apple Hardware test, saying that there might me a problem with the SMC (ref.-Code PFM006).

I already tried to reset the SMC, but it didn't do the trick. Well, as iStat Pro does not show any temperature for the ambient temp sensor, I presume that there must be a problem with this sensor. I already searched on the internet but never found a proper solution for this model, although my suspicion seems to be legit.

So I opened up my imac and found two spots, which don't seem to be in good/original condition (this is where I should mention, that I bought this mac in used condition). I uploaded some pics, hope you guys are able to help me out.

I compared those pics to the iFixit Teardown for this model and found that there seems to be a missing resistor close to the network port (btw. is the chip, which is coloured in pink the SMC?)

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Does anyone know the exact type of this resistor?

Additionally I am under the impression, someone already tried to fix the mac, as there seems to be an unusual solder joint/shortcut close to the backlight inverter. I also guess this joint should be replaced by the proper resistor.

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Maybe there is someone out there having access to the scematic of this board and able to tell of which type this resistor is?

Thanks in advance, any help appreciated!

Btw.: Does anyone know where to get the schematics or the board view from?

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@oldturkey03 - Do you know what the values are?


@lycos what is the number on your board?


@oldturkey03 Hi, its 820-3588-A. Thanks in advance.


@lycos get a schematic and boardview here

I don't have one myself (never get iMacs for board repairs) but it looks like the thermal sensor chip circuit which is on the MacBooks, so this explains the issue you are having


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@lycos let's see if this will help

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R5300 is a 2.2K 5% 1/16W resistor in a 0402 package (part of the SMBus Connections)

FB8100 is a 600 Ohm 25% 0.5A 0.40 Ohm inductor in a 0603 package (part of the LCD Backlight Driver circuit)

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Thanks a lot. I will try to get my hands onto those parts asap.

@oldturkey03 So a missing R5300 could be the culprit for the missing temps and/ or the fan run off, am I right?

I wonder what happend to the FB8100 and what exactly this solderjoint shortcut could cause in a worst case szenario.

Thanks a lot.


So here's my final update ;)

Today I replaced both SMD parts by those mentioned by oldturkey03. Well, now the iMac works like a charm! No fan run off, no missing temps, just normal.

Thanks to all of you guys for your instant help!



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Basti will be eternally grateful.
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