Friday, May 29, 2009

Repairing the SATA slot on a HP Compaq 6710s laptop

About a month ago I found an ad for a HP 6710s, with a Core2Duo T7100 CPU, 2GB RAM and a 160GB hard drive, WiFi, BT, DVDRW LS, and a carrying bag. The seller mentioned that there was some kind of a problem with the hard drive slot, and sent me a photo of the problem (the image on the left is that original photo, I just added the red highlight circle).
I purchased this laptop for about $170.
The problem was that while inserting the hard drive, the previous owner broke off the plastic framing of the SATA connector, and also broke off one of the pins. This defect basically made the laptop useless as there is no way to make sure that the hard drive will align well with the exposed pins, and moreover, there was no way to know if the hard drive would actually work as one pin from the SATA slot was missing.

(Click on the images to view them in full size)

As you can see the pins from the image on the left, the SATA Connector pins are exposed, and one pin is broken. The pins originally were wrapped with a plastic shield that served both as a protector and as a rail that ensured correct alignment of the Hard drive’s connectors with the pins on the motherboard. This plastic housing also ensured that enough pressure is applied so that the hard drive’s pins have good connectivity with the pins on the motherboard. Without a functional SATA slot, there is no way to use the laptop.

So, we are facing two issues: the broken plastic shield, and the broken pin.
The broken plastic shield problem is not so difficult to solve. I used an acrylic based glue (a.k.a. Super glue) and glued back the torn off plastic wrapping. On the image on the right, you can see the aftermath of the operation, where the SATA connector is restored back to its original form. But before we get to the phase of the superglue and sticking back the plastic housing, we need to see what this missing pin actually does.
Since we’re dealing with a SATA slot, we should know a bit about it. Unlike the IDE/Parallel ATA slot, this technology creates a data stream i.e. a line of bits, therefore the name of SERIAL ATA. So all it takes for a SATA drive (in theory) is just one wire to transfer all the data, unlike the PATA that uses 40 pins interface. The SATA slot has two groups of pins: the smaller one that is the DATA part, and the larger one that is the POWER part. So, small group for data, big part for electricity.

Let’s now get back to the problem. As you can see, the missing pin is fourth from the top down (look at the red circle in the previous image on the left) on the Power group. Now let’s take a look at the hard drive’s connector and locate the matching pin to this missing one on the SATA connector.

(Click on the images to view them in full size)

Looking at the hard drive reveals the cause for the broken off pin. The image on the left indicates the matching pin on the hard drive with the missing pin’s position on the SATA connector, while the detail on the right points as to what damage was made on the hard drive’s plug when the pin from the SATA connector broke. The previous owner obviously pushed hard enough to break both the plastic shield and make this large dent on the hard drive socket itself. One hard push and he had to give up his laptop for a bargain price. But let’s move on.
In order to find out what this fourth pin does, I took the laptop’s hard drive and with a multimeter measured the resistance between the fourth pin and the surrounding pins. The interesting thing was that the fourth, fifth and sixth pins had zero resistance between each other. This means that this group of pins actually worked as a single pin. A bit more snooping resulted in figuring out that the 4-6 pins group was grounding. This snooping was to simply check which wire goes where, on a Molex to SATA power connector adapter, but that's beside the point.

(Click on the images to view them in full size)

The above images are from the internal side of the hard drive’s printed circuit board (PCB). The image on the left shows the two connectors: the Data (on the left, the smaller one) and the Power (on the right, the larger one), with the red arrow indicating the fourth pin matching the missing one from the motherboard.

The key to solving this fix is the image on the right
. Notice that the pin group 4-6 (highlighted in the red circle) is interconnected. All three pins are short circuited via the PCB wiring, which means they all function as one pin, as mentioned earlier. As this is in the Power group of pins, and on top of that, pins 4-6 are grounding, there will be no problem to simply ignore the missing pin 4, as pins 5 and 6 will do a sufficient job of grounding. So the fix then is only to glue the broken plastic wrapping, as mentioned previously, and that is it.
For over a month now, the HP 6710s works flawlessly, and I’m actually typing this text on it. The repair for the SATA socket took less than 10 minutes, and that got me a perfectly working laptop for a bargain price.

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