MacBook Pro - HDD works when connected externally

I'd try replacing the SATA cable from the board to the HDD first. Might be a cheap fix.

niteflyr said:

I'd try replacing the SATA cable from the board to the HDD first. Might be a cheap fix.

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This is a good tip & should always be the first point of call, many people forget to check the cabling when troubleshooting issues.

If you can do the logic board replacement easel and cheaply it might be worth that, but if it's not going to be highly cost effective, sometimes it's better to just accept age and move on to a newer machine.

I seem to recall that 2009's were prone to cable failures.

You should definitely NOT replace the logic board without finding out what the problem is. The most likely cause is the SATA cable, although it could be the logic board or a connector as well. The only commercially available product on the market that can test for those types of problems is Scannerz in interface testing mode, because that's what it was designed to do (the link for the product is: http://scsc-online.com/Scannerz.html) but it does cost money.

The other option is really just to trial-and-error it with a new SATA cable. The odds of the SATA cable being at the root of the problem are simply too high to be overlooked.

If if does end up being internal, you could always get a Firewire 800 box for the drive and just use it as a desktop unit.

It's the cable. You can do advanced diagnostics on it if you want to but it's the cable.

I bought an external WD months ago and it had just about the cheapest USB cable supplied with it that I've ever seen. It looks like it was built by a bunch of elves. I wanted to keep a clone of my main drive on one volume and then use the other volume to do Time Machine backups. It worked OK for about a few weeks then got flakey.

I read about Scannerz on here so I got it. When I did a scan, it kept getting erratic irregularities, which means it's taking too much time for an operation to proceed properly. I started moving the cable around and I could actually induce errors during a Scannerz test, and lots of them too. I just replaced the USB cable with a decent one, you know, one that wasn't built by elves. No more irregularities, no more errors, regardless of how I moved the cable around.

The nice thing about testing a cable with an external drive is that you can move it around and actually induce problems. The problems had to be in the data lines instead of the supply lines otherwise the drive would probably show up as being improperly ejected. If I understand it properly, when data transfers don't complete properly because of a weak and erratic connection, they go through a ton of retries which takes a lot of time, and that's what Scannerz picks up as an irregularity. If I'm wrong about that, someone please correct me.

I don't think you can quite so easily test an internal cable unless you want to try moving the HD around while the unit is open, which sounds kind of risky to me. I suppose it can be done though.

The SATA cables on a fair number MBPs are known to be a problem. I definitely would not replace the logic board without replacing the cable first.

Scannerz defines anything that takes too long to process as an irregularity. If it's a weak sector on a hard drive, the HD controller will need to re-read the sector many times before it gets it right which takes longer than normal. If there's an intermittent connection, when the data line is open the interface error checking detects the error and forces a retry, and it takes longer than normal to process. Both operations take longer than normal to process which is why Scannerz picks them up.

I've seen HDs with weak sectors take almost the exact same time to process during a re-test, but bad cables never repeat either in time or on disk location. I suppose it can pick up other stuff too but that's all I can think of at this time.

With all that said, for those that can open their units and service them, the problems could be picked up if you booted off an external drive, used the internal drive as a scan target, and then used a non-conductive probe to prod the SATA cable. I did this once with a flakely IDE cable on an PowerBook G4 and the test results went bonkers.

Internal laptop cables just can't handle much abuse.