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モデル番号A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5もしくは 3.4 GHz Core i7 Processor, ID iMac12,2

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HOW TO FIX iMac 27" missing ferrite bead L5500 / fan speed issue?

Hi everyone,

I’m new here, and I have a question for the experts of the forum. I have an iMac 27” Mid 2011 (A1312 / 3.4 GHz - 8GB RAM) that I purchased online months ago from a person that lied about its conditions: the hard drive is failing, and the graphic card died on me about one month ago.

I replaced the graphic card with a new one, and when I put everything back and turned the iMac on everything was working again, except for the CPU fan that started spinning like crazy. I downloaded and installed Macs Fan Control, and according to the app the values are the following: ODD 3800 - HDD 1100 - CPU 4200. As you can see, the only temperature sensor that is working properly is the hard drive one. At the moment I don’t care about the optical drive since I never touched it and it’s still working regularly.

Despite being extremely careful and using appropriate tools, believing that I have damaged the thin cables on the CPU heatsink and fan I replaced both (for just $6 each), but the problem persists. Thankfully, during the repair process I took many photos and videos. Comparing the before and after photos I noticed that I lost the ferrite bead L5500 close to the AMBIENT TEMPERATURE connector, and a very small portion of the motherboard trace connected to it came off, too (L5501 is still in its place). Not sure how that happened since, as I said, I am extremely careful and never use screwdrivers to remove cables, plus this is not the first time I open computers and unplug thin cables for repair. After reading that many other users lost ferrite beads in the same area and are now experiencing the same issue with the fans, after inspecting my motherboard for other possibles damages and/or missing components and not finding any it’s my understanding that this is really some kind of factory defect as other people complained about.

I grew up watching both my granddad and my dad repairing electronic stuff, but unluckily I don’t have exceptional soldering skills. While I can always learn how to solder things, unluckily I cannot read schematics, don’t know how to use a multimeter, and know nothing about ohms, volts, etc, but I am a resilient person and I am positive that I can fix this iMac by myself the same way I fixed other things in the past to save money. My dad lives in a different Country and I live in the US, so shipping the motherboard to him is out of question. After spending almost $200 for a new graphic card, CPU fan, heatsink, and thinking how much more I will have to spend for SSD, 2.5” to 3.5” mounting bracket and OWC In-Line Digital Thermal Sensor, I really need a quick, easy and cheap solution.

I keep on reading online that it is possible to fix this kind of damage by either replacing the ferrite bead with a single trace of solder that covers its pads on the motherboard, or by bypassing the damaged area with a “bridge” made with a small electric wire. I think the latter could be the best option in my case since it looks like one of the two pads and part of the trace got ripped. I’m just not sure where to start, so I really need some help. The explanation should be very elementary. Images/drawings will help a lot, too!

Here’s the photo of the damaged area of my motherboard (the red line you see is the copper trace that came off):

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I know I am not the only one experiencing this problem, so your replies will be extremely useful for many other iMac users, too.

Thanks! :)

Update (08/12/2019)

I’m adding two additional photos that I took a couple of minutes ago, one with a regular flashlight and the other one with the UV light on to highlight the damage underneath and around the missing L5500 ferrite bead. Hope this helps….thank you!

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It doesn't look like a difficult repair as the missing trace can be repaired with a jumper; I would avoid cutting off the inductor or bead that was lifted if possible. However if you can add the board number (820-xxxx) it will be easier for others to check schematics and help you.

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Hi @arbaman, thanks for your reply! My board number is 820-2828-A. The bead unluckily is totally gone.

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@lauramacfan Hi Laura, unfortunately I'm just into portables repairs and I don't have the relevant schematic at hand..I'm sure someone will drop by with some help though.. @oldturkey03 maybe ?

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@arbaman Same micro solder process as when you pull a fan connector off a laptops board (I think we have all managed to do that ;-) She'll need a donor part and a good microsolder tech to do the job.

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@mayer That sounds very reasonable, just trying to keep on the safe side here having seen very few iMac boards ;)

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@arbaman @mayer It’s been hard to find it, but I think this is the schematics page you were looking for. It should be the “Ambient Temp Sensor” because I read L5500, and the FERR-220-OHM which is the ferrite bead that came off of my motherboard. Hope this helps!

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@lauramacfan, that is correct. You have the right schematic and both inductors are identical. Your repair is straightforward. Carefully scrape the copper trace with a thin razor blade (I use a scalpel to expose as much of it as possible. Then solder a thin wire ( a strand from an old lvds cable or similar will work. I use wire from an old transformer). Solder that to the trace. Use plenty of flux and tin the copper trace first, it'll help to make the wire stick better. Then solder the inductor to the pad that is still existing and solder the wire to the other end of the inductor. Or you could just directly connect it to the connector. You got that!

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Thanks a lot, @oldturkey03! Your explanation was exactly what I needed! I only have a couple of questions:

1) I know that the inductor I need is a "FERR-220-OHM" size 0402 (1005 metric) and I found a website where they sell them, but I noticed that the same ferrite beads come with different maximum DC current, maximum DC resistance, tolerance, voltage rating, watts, temperature coefficient, etc.. What I couldn't find anywhere online is which one of those is the correct replacement for L5500. This is the website: https://www.mouser.com/Search/Refine?Key...

2) When you said "Or you could just directly connect it to the connector", what do you mean? That I can avoid using an inductor, and I can just add a thin trace of solder that covers the area where the missing inductor is instead?

Thank you!

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@lauramacfan I was referring to connecting the wire with the inductor soldered to it, to the connector vs the broken trace. For the inductor itself I would go with a low resistance and ,since it it s sensor circuit with a few hundred mA. Something like 450mA and 270Ohm

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After you fix the connector, your fan will still race. Apple used built in priority thermal sensors on their hard drives to prevent the use of any third party hard drives. The solution is to us the OWC Thermal Sensor:

https://eshop.macsales.com/item/OWC/DIDI...

UPDATE

Replacing the logic board receptical is not that hard if you have a hot air work station, stay hands and experience. I’d call around to the local Mac Techs and ask if they have the ability. The cost should be able $25-$30 if you take them the logic board. You want to carry it in a special non-static bag and the tech may loan you one.

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Hi @mayer, thanks for your reply. Both the hdd, its thermal sensor and its fan are working normally. The hdd hasn’t been replaced yet, so it’s still the original one. The problem (with the CPU fan) started when the ferrite bead L5500 came off, which is one of the two connected to the Ambient Temperature connector on the motherboard. As already demonstrated by other users and from what I found online, using that (expensive) thermal sensor won’t fix this issue if you, just like me, are still using the original hard drive and haven't touch anything connected to it. That is something that happens after replacing the original hard drive with a SSD or with non-compatible hard drives. At that point you will have to use the OWC Thermal Sensor. I'm not there yet, and will not replace the hdd with a ssd until I'm sure that I can fix the damage on the motherboard (I've already spent too much for this iMac, but I love it and I'd rather fix it by myself and keep it than having to sell it piece by piece to afford purchasing another used one).

As you can read in this post, user @Elly Walkie was able to solve this problem by adding a trace of solder to replace the missing bead: Faulty CPU/ODD sensors or fans after Dual Drive Kit Upgrade

My idea was to do the same exact thing, but I'm afraid my damage is more extended because I'm also missing part of the copper trace on the motherboard. That's why I was asking if it would be a better idea to create a "bridge" to bypass the damaged area. Unluckily I have no electronics skills (I can't read schematics), so I’m here asking for help.

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@oldturkey03 That’s how I scraped the trace of the missing inductor L5500. I did it for about 3-4 seconds until it became white. Now the copper is finally visible where the trace got broken. I hope I haven’t overdone it with the tiny screwdriver:

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@lauramacfan looks a little rough but it may work. If anyone shaves in your house use a razor blade (crack those cheap safety blades open and remove the blade to use as a tool ;-) Just nice and careful scraping with the blade at a shallowing angle should remove the material. Now you need the inductor to start soldering :-)

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@oldturkey03 How much of the trace should I still scrape (in length and/or depth)? Should I reach the pad that I circled in green in the picture, above the word "AMB", and start soldering from there, or am I good to go? (The red line I have drawn is just to show the length of the trace that I’ve already scraped):

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The closest thing to the specs of that inductor that I found online is this one..is it ok? https://www.mouser.com/ProductDetail/Mur...

I’m waiting for some tools that I bought online for less than $30: two fine tips for my soldering iron, flux paste, a desoldering vacuum pump, and a multimeter. As soon as I know what inductor I should purchase I’ll get at least 10 of them (because I don’t believe in “beginner’s luck”...). I guess I’ll have to wait a couple of weeks before I can start with this repair! :(

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@lauramacfan you can solder some thin wire right to the pad instead of scraping more material. It could make it easier to solder as well. I am not really a friend of vacuum pump and prefer to use soldering braid with lots of flux on it but you need to find out what is comfortable for you. that inductor should work

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Laura MacFan さん、ありがとうございました!
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