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

IanD1953

Level 1

50 points

Posted on Oct 3, 2017 6:38 PM

I bought my MacBook Pro mid 2012 version back in August 2013 and I am just replaced the HDD cable for the third time.

I had kept the three old cables so I decided to find out what had gone wrong with them. There are 5 thin copper tacks, which connect to the 7 pin side of the SATA connector. I used a multimeter to do a continuity test on these tracks. I found that on all three cables one of these tracks had broken at the same place. The cable does a tight right angle bend at the point it passes over the optic drive. The cable flexes at this point and eventually one of the copper tracks breaks. I found that if I flexed the cable at this point the track would make and break contact.

On later versions of the MacBook Pro Apple modified the HDD mount so it would prevent the case from pressing on the HDD cable. They also introduced an upgraded cable 821-2049-A, which replaced the original 821-1480-A. Unfortunately, upgraded cable still eventually breaks. This time I have taped the cable to the optic drive to try and prevent it flexing. Time will tell if this helps. The cables are quite easy to replace and I keep a few in stock.

One way of partially checking the problem is to externally connect the HDD (e.g. use a dock or SATA to USB cable) and see if the MacBook boots correctly. You need to hold the alt key down when starting the MacBook to be able to select the external drive.

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62 replies

RMFT76

Level 1

4 points

Apr 17, 2018 6:12 AM in response to Grant Bennet-Alder

I got the impression that Apple had accepted there was something of a design fault with this cable and that at one time they had a policy of replacing it for free and although that policy had expired, as a gesture of good will, they were prepared to honour it in my case.

l008com Author

Level 1

101 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.

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Diagnosing MacBook Pro Hard Drive Cable Failure