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Repairing an intergated USB hard drive

 

 

This is the story of a job that should never have been needed, were it not for a couple of bad ideas that combined to snatch defeat from the jaws of victory. It is also related to the story of Repairing a Thumbdrive in that they involved surprisingly similar circumstances, and they both happened over the course of a week.

I was at The Hackery again when a call came in from a teacher at a local school. Another teacher there had suggested she call us about a big problem that had developed. Her external hard drive was not working, and surprise surprise, it contained the only copies of a bunch of important data. Bad idea number one. The data recovery place she'd called had suggested it might cost a thousand dollars to repair. So she was asking around for a second opinion. We told her to come down.

She soon brought in a 500 gigabyte Verbatim 2.5" USB hard drive. Sure enough it failed to detect on our machines. So with the silicone rubber shell cut open, we slid the hard drive out with the intent of plugging it straight into a SATA port to see if that would bring it back to life. Unfortunately what we found inside was bad idea number two.

Traditionally, external hard drives have been nothing but standard laptop or desktop hard drives mounted in a case with a small adapter plugged into them to convert between SATA and USB. This meant you could pull off the adapter to get a standard drive, which is very handy if your USB to SATA adapter stops working. But some "genius" decided that this was too costly, and so an increasing number of external drives are being manufactured that have the entire USB converter integrated into the drive PCB. This means there's no SATA plug anywhere on them, and no way to separate the USB adapter from the drive itself. It was one of these drives which our customer had brought us. Joy.

 

So we had a drive that couldn't be isolated from its USB controller. And when we examined it beneath our magnifying lamp, we could see that it was indeed the USB controller which was at fault. A blow to the USB port had not only broken its connection to the PCB, but also bent the PCB to such a degree that many traces on the opposite side (Where the SATA-USB bridge chip was located) had torn right off. A traditional repair would be very difficult.

Instead I proposed a more radical solution. I would attempt to disconnect the USB-SATA bridge chip from the drive controller IC and tap into the SATA signal lines, so that the drive could be accessed by way of a PC's SATA connector. In effect I was going to transform it back into a normal laptop drive. Power would still be supplied over the USB port though as the power lines had remained connected. Were it not I would have also wired a standard molex socket to the drive.

The first step was to look up the bridge chip. The markings on the top indicated that it was a JM20329 by JMicron. And a quick trip to Google unearthed the datasheet. Then I went looking through the pinout of the chip until I located what I needed. Page 6 showed that pins 20, 21, 25 and 26 were, respectively, the positive and negative RX lines, and the negative and positive TX lines for the chip. These are the 4 pins that make up a SATA data cable. And that meant the traces which lead to these pins were carrying the signals which would normally be found at the drive's SATA connector, if it were so equipped. Jackpot.

 

The datasheet also helpfully told me that the controller expected to be connected with a capacitor in series on each of those lines, so I knew that the 4 capacitors to the bottom/right in the picture above would need to be removed if I wanted to connect the drive directly to a PC. A good thing, as it presented a handy location to solder to.

I cut the end off of a standard SATA data cable and stripped it down. Beneath a foil shield was 2 wire pairs, one of which carried data from the drive to the controller, and the other which carried data in the opposite direction. I neatly stripped a tiny bit of insulation off the ends of each.

Then it was time for some extremely delicate soldering. I had brought my stereo microscope from home for this job, as I couldn't see clearly enough with my naked eyes.

 

Here I am first removing the tiny surface mount capacitors, then soldering the 4 wires to the pads the capacitors had occupied.

 

And here's the end result, with the electrical tape holding the SATA cable roughly in place to keep the tiny solder joints from breaking. Were I to do this again I would use thin magnet wire as a bridge between the extremely stiff SATA wire and the tiny solder pads. But it was attached, and that meant it was time to test.

 

We carefully plugged the drive into the drive test station...

 

And it worked! The drive spun up and mounted! We began copying the data onto another drive the customer provided as fast as we could. And a good thing, too, for the tiny traces on the PCB tore off when we disconnected the drive at the end to show the customer. It held out just long enough and not a minute longer.

So what can we learn from this? Well, I know it's been said many times before, but please, BACK UP YOUR DATA! The world's most reliable hard drive can't replace a backup. But I think there's another good lesson here too. If you have the option, it shouldn't cost much more to buy a drive that uses a normal SATA mechanism inside. And an extra few dollars or an extra 1 cm in case length are a small price to pay for having the flexibility to directly communicate with your drive if something goes wrong. Unfortunately it can be a little hard to tell from the outside of the box what's lurking on the inside. It's for this reason that I usually assemble my own external drives using separately purchased hard drives and drive boxes. And that's a great little project for someone who wants to gain some technical experience.

Page created July 24th 2013

Seemed like the real thing only to find... Mucho mistrust, love's gone behind.