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l008com Author

Level 1

92 points

Diagnosing MacBook Pro Hard Drive Cable Failure

I've been fixing Macs professionally (not through Apple) for well over a decade now. By far the most common thing I do is replace failing hard drives. While Apple's own tools (hardware test, Disk Utility) do almost nothing to positively confirm a failing hard drive, there are several other tools (SoftRaid, SMART Utility) that can read the SMART data and tell you for sure that a drive is failing. So unlike the Genius bar, I can quickly diagnose a bad hard drive without having to infer the problem through symptoms.

But one problem that I've noticed really being on the rise lately, is a failing hard drive cable in MacBook Pros. That's the little flat ribbon cable that connects the hard drive to the logic board. It also connects the sleep light. This is a much harder problem to diagnose, because it generally acts just like a system with a failing hard drive, but the drive will pass a real SMART test with flying colors. You might think "come on, how often does a simple cable really go bad?" Well, I've never had a traditional desktop style SATA cable go bad. But I've replaced a lot of these drive cables and I'm doing another one tomorrow. I never really know if it's going to fix the problem or not though...

... because, there's no way to directly confirm the cable is the problem. I know all about Apple service procedure. I know the official way to diagnose a problem is to start replacing parts until the computer is fixed, and that last part was your problem. But that's not how things go in the out-of-warranty world of independent Mac repair.

So I got to thinking. Computers with bad cables don't crash, or freeze. They just hang for a while randomly, then come back. JUST like a hard drive with lots of bad blocks. So what could be causing this? The only thing I can think of is SATA bus errors that only happen intermittently (on a scale relative to the amount of i/o calls a hard drive does). If that is the case, then there must be SOME kind of utility somewhere that can see these errors? There are plenty of utilities out that that have fancy 3D interfaces, but do absolutely nothing (tech tool etc). But there are a few tools that the Pros use that actually DO stuff. DiskWarrior and SMART Utility are the main tools. If I could find something that can somehow easily and definitively sniff out these bad SATA cables, that would make my life a whole lot easier.

Posted on Dec 20, 2016 4:44 AM

Top-ranking reply

wiseacre33

Level 1

14 points

Posted on Nov 3, 2017 10:44 PM

Thank you for your explanation of the 821-2049-A and 821-1480-A cable differences. I couldn't find that anywhere.

I just inherited a mid-2012 13" A1278 which previous owner said she hardly used in recent years because it got so slow. After resetting the system, wiping the drive and upping the memory from the original base 4gb to 12gb, I noticed a definite improvement. But still really slow and sort of hanging up when installing new OS and other large apps. Even now on MS Office 2016 and Final Draft I get a lot of beachballing. I'm thinking I should try swapping out the Hard Drive Cable and maybe put in a spare SSD I've got lying around while I'm there.

So the cable iFixit sells says it can replace both. But it's pretty costly at $44 (with bracket). I can find some others (with bracket) on Amazon for half of that. But those specifically say they are EITHER for the 821-1480-A cables OR the 821-2049-A cable. Not both. Should I just go with the newer version 821-2049-A?

You also mentioned that Apple modified the HDD mount so it would prevent the case from pressing on the HDD cable. Even tho you said it didn't eradicate the issue, is that something that I can easily accomplish by replacing both brackets?

Any advice would be greatly appreciated.

Thanks.

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62 replies

lota68

Level 1

4 points

May 1, 2018 2:49 PM in response to l008com

I think you're absolutely right about a failing hard drive cable making intermittent I/O errors at some proportion.

Unfortunately the only diagnostic tool I can think of requires the laptop to be booted and can be displayed in the console app.

I recently diagnosed a failing cable that caused a computer to run slowly. The console app showed a cascade of of I/O failures during periods of the cable failing. It might be a good thing to check.

IanD1953

Level 1

42 points

May 7, 2018 4:48 AM in response to lota68

That’s an interesting comment, which relates to something I have been puzzling over for sometime. I used to find that Microsoft Office applications took a long time to load. Then for an unrelated reason I upgraded the memory from 8 GByte to 16 GByte and much to my surprise I found that Office applications were loading much faster. A few days later the HDD stopped working so I installed a SSD and got as far as loading OSX before it also stopped working. I then realised that the problem was just a faulty cable.

One suggestion I was given at the time was that the cable may have been faulty for sometime and it was causing a high bit error rate and that opening the MacBook’s case may have disturbed the cable. It is only academic but I wonder if anyone else has any other ideas.

May 7, 2018 6:56 AM in response to IanD1953

IanD1953 wrote:

It is only academic but I wonder if anyone else has any other ideas.

Hasn't this thread been beaten to death?

Academic or otherwise—I can say when Apple replaces a HD they always replace the SATA cable at the same time—this should be instructive.

May 31, 2018 1:35 PM in response to l008com

I'm currently dealing with this right now as well. I'm repairing a mid-2009 MBP that's never been updated. The girl said it wouldn't start up and would just show a blinking folder with a question mark. Eventually I removed the hard-drive and plugged it into my desktop and was able to run first aid. I've only gotten the original MBP to read the disk once, but a snow leopard install failed and it hasn't read it again since. It's still pulling up just fine on my desktop. It's a real pain in the ***. The only upside is how easy it is to replace these cables.

IanD1953

Level 1

42 points

May 31, 2018 3:08 PM in response to BadAnderson

It might be worth checking if the cable is shorting to the case. The inside surface of the case of some earlier MacBooks had a slightly rough surface which could wear through the cable's insulation. This problem is mentioned earlier in this thread.

Jun 6, 2018 10:25 PM in response to l008com

I just had one of these faults and thought I'd add the symptoms here to help others. I had an SSD in the Mid-2012 MacBook Pro hard drive slot, and all of a sudden, it's speed dropped dramatically from 400MBytes/second to 5MBytes/second. Removing it and putting it in a USB3 external housing restored the speed. You guessed it - replacing the drive cable (again) restored the full speed. Now I've bought a few more cables to have in stock, ready for the next time.

l008com Author

Level 1

92 points

Dec 21, 2016 3:02 AM in response to l008com

Since writing this, I just came across ANOTHER 2012 13" macbook pro, with a bard hard drive cable. The computer powered on just fine but wouldn't boot. Booted off any external source no problem. Put it's hard drive in a case, it worked just fine. But booted off an external volume, the machine couldn't see it's hard drive at all. Replaced the drive cable, and it's operating normally. This is an absolute epidemic of failed hard drive cables. If only there were an easy way to diagnose this on the go.