Waking up in Geelong

In my family I am known as ‘Mr Fix It’, so it was not surprised when my sister told me the other week that the power plug for her Samsung laptop computer (model number NP305) wasn’t staying put, and asked if I was able to fix it. I said yes, and took a look.

It turns out this wasn’t the first time that the power socket had developed issues – when it was only six months old my sister had to send it back to the manufacturer under warranty to have the very same issue rectified.

The guys at Samsung didn’t need to spend too much time fixing it – the repair sheet said that they only replaced part number BA92-09477A. Unfortunately for me that is the entire motherboard, and after discovering that the price of a new one on eBay was over AU$140, I decided not to take that route!

However when I continued searching I found a much cheaper option – a replacement power jack by itself. eBay sellers in China were asking AU$2.50 for a single unit with postage taking a month, while sellers in Melbourne could get it to me in a few business days for AU$10. I took the latter option!

While I waited for the part to arrive, the first step of the repair was opening up the laptop. I wasn’t very successful in finding all of the screws by myself, but thankfully I found a teardown video of the Samsung NP305 laptop online.

I only needed to strip down the laptop until I reached the motherboard: I was able to leave the LCD screen, keyboard, trackpad, etc all in place on the main laptop chassis. I was also able to keep the RAM, CPU and heat sink in place on the motherboard.

The defective power jack was attached to a corner of the motherboard, and was soldered in seven points to the motherboard: four mounting pins spaced around the edge, and two negative pins and a single positive pin at the back.

However when my replacement power socket arrived in the mail, I ran into a major problem. Every eBay listing depicted a power jack that looked like this:

But the part I received was a mirror image – when the socket was aligned to place the open socket to the left hand side, the four small mounting pins faced the opposite direction, and the positive power pin was beside the two negative pins, not offset to the side.

A second problem I ran into was removing the old power socket from the motherboard. I had a solder sucker, solder wick and a soldering station all at my disposal, but getting the seven soldered joints undone was beyond me.

By this point I decided to cut my losses, and just remove the old socket by cutting away the pins with side cutters, giving me clearer access for desoldering.

Once I wrenched the old socket free, I had a brainwave: the reason the new socket is a mirror image of the old one is because it is designed to be soldered to the opposite side of the motherboard. To test my theory, I connected both the new and old sockets to the power supply, and tested the polarity of each of the output pins – and the voltages on each pin were the same.

After soldering the new socket in place, here is the finished repair.

When viewed from the outside of the laptop, the most important thing to do is ensure the power socket is offset towards the RJ45 network jack alongside – failure to do this means the cover won’t fit back on!

Dropping the new part into place wasn’t as simple as I though, but I eventually got it in there and soldered. The one gotcha was the position of the positive pin: it was offset from the original pad on the motherboard, so I had to bridge the gap with a short length of wire and a lot of solder.

With that all done, I crossed my fingers and plugged in the power cord. Thankfully no smoke came out, just a green charging LED turning on, so I reassembled the laptop, and it booted successfully.

All up I saved AU$130 compared buying a replacement motherboard, or around $50 compared to paying a laptop repair shop to to the job for me.

How to replace the power jack of a Samsung NP305 laptop

Here is a step by step guide:

1. Pull apart the laptop to extract the motherboard – here is a teardown video. You can leave the RAM, CPU and heat sinks in place on the motherboard, and the LCD and keyboard attached to the chassis. (photo)
2. Find the old power jack, and for for future reference make a note of which way the offset socket faces. It should be facing towards the network socket, with the blank plastic part facing the edge of the motherboard.
3. On the component side of the motherboard (same side as the heat sink), cut the four mounting pins between the old socket and motherboard with side cutters. The pair beside the network jack will be harder to get access to. (photo)
4. Cut the three power pins between socket and motherboard with side cutters – these ones are a lot more harder to get access to, because of the plastic surrounding them.
5. Now that the old power jack is free, remove it from the motherboard.
6. Test your new and old power jacks side by side outside the laptop: connect them each to the power supply in turn and check that the presence of voltages between each pin are the same in both cases. Ensure you orientate the sockets in the same way each time, with the ‘extra’ bit of plastic to one side.
7. Place the new power jack into the space left behind, ensuring that the offset power socket faces in the same direction as the old one did (photo). The seven pins of the new socket will face the solder side of the motherboard (opposite side to the heat sink).
8. Solder the four mounting pins in place, ensuring that they are pressed right up against the motherboard. Failure to do so will result in it being very hard to get the case closed correctly.
9. Now solder in place the two negative pins to the socket: these go directly to the two solder pads located at the outside edge of the motherboard.
10. Finally, solder in place the single positive pin to the socket: it goes to the single solder pad beside the network jack. You’ll need to add a short piece of wire to bridge between the pin, and the original offset solder pad. Also take care not to damage the SMD components next to the pin doing this, and make sure you don’t bridge them with solder either. (photo)
11. Reassemble the laptop, ensuring that the back of the case fits easily over the new socket, and the opening in the case lines up with the jack. If it doesn’t, then you’ll need to pull it all apart again and resolder the socket.

Sources

• Samsung NP305 laptop teardown video
• Samsung BA92-09477A motherboards on eBay
• Replacement power jacks for a Samsung NP305 laptop on eBay

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