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Broken Power Supply Unit

October 22, 2011

My laptop is now almost four years old and the list of broken components is long:

  • battery
  • microphone
  • CD/DVD drive
  • external VGA
  • Bluetooth
  • display backlight dimming
  • LAN connector (slack joint)

But so far, no grave failure occurred, means, nothing I could not circumvent. Until today. When I woke up, I was not able to power up my laptop.
In short: it was the power supply and it is fixed. But I want to explain how I fixed it because it seems to be a common problem with laptop power supply units. This is not meant to be a tutorial though, only a story of success. :D

The Symptoms

So, the laptop does not power-up. No LED blink, no fan sound, nothing. So I take a closer look at the power supply unit. But what’s that? There is a vague beeping sound coming from it. Not a mechanical one like one can sometimes hear from old television sets but an electronically generated one. I recorded it using a sensitive microphone.

I do not know what that actually is, but it sounds to me like something is trying to start over and over again.

Troubleshooting

A closer look at the wires also discloses a suspicious bump near the bend protector.

So I use a multimeter to measure the output voltage. Bingo, no output at all.

I wonder why they put a bend protection there when it is so stiff that the bend will just happen a few centimetres along.

Get your Hands Dirty

The bump in question is too close to the case of the adapter to fix it in place, so I have to open the case. This also gives me access to the solder joints, so I can futher determine, if the wire is really the problem.

Note: Do not open electric devices unless you know what you are doing! Electricity can kill you.

So, to open the case I need a … saw. Yes, a saw! And a box cutter and a big screw driver to break the case open.
Ten minutes later, the case gives in.

In there I find a metal casing that is actually soldered on the circuit board in two places.

Time to heat-up the soldering iron.
Beneath the metal casing, there is a cardboard mantle and thereunder the actual hardware with lots of what looks like tooth paste and might be silicone. And it is everywhere!

The solder joints I need are easily accessible, compared to the rest. Using the multimeter to test the continuity between the solder joint and the connector confirms the suspicion. ~0 Ohm from one joint to both contacts of the connector. A short circuit.

I do not have my desoldering pump here, so I have to use braid. I hate braid.
Well, I am just glad that I did not toast one of the close-by units.

So, a few minutes later …

And there it is! Looks like someone took a bite. :)

A few more minutes later …

My solder joints look awful, I know. I am a bit rusty with this.

And look what I found and what is not from me:

Yes, there is a gap of three millimetres!

Rewind the Rest

The metal casing has to be soldered to the board again. After that I check continuity to the ground contact on the other side of the board, to be sure, everything is alright.

The main case is severly damaged from the opening procedure, so I use two wire straps to hold it together.

Be Happy

So, everything is a bit more ugly but works as fine as before. I am glad that I tried that before ordering a replacement power supply for 59 EUR.

So if your power supply unit or anything else stops working, try asking the Interwebs for some suggestions. Most problems have been there before and the discussions might give you some clues on how to fix it.


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12 Comments leave one →
  1. October 22, 2011 3:50 pm

    I always like when somebody tries to fix broken things instead of throwing away as waste and buying a new one. Good job.

  2. October 22, 2011 4:56 pm

    Great. Gives me motivation to try fixing my old laptop with some hardware trouble myself now! :D

  3. Vladimir Prus permalink
    October 24, 2011 6:03 am

    Funny, I’ve just opened my AC brick to do a similar repair a few hours before reading this post. Now, given that I solder once every 10 years, I don’t even have a braid around, which delays this project by one more week ;-)

  4. October 24, 2011 6:25 am

    @Andras: Thanks. And it is a good feeling, too.

    @Vishesh: Do it! Once you accept, it is already broken, things become easier. :)

    @Vladimir: Hehe, yeah, I had to dig deep as well to find the equipment. :D

  5. Paul Gideon Dann permalink
    October 24, 2011 9:49 am

    I wonder if that stuff was thermal paste?

  6. October 24, 2011 10:30 am

    Probably not. It was rather hard. And thermal paste is only efficient when it fills the air gaps between two adjoining uneven surfaces.
    I guess the silicone is there for better shock resistance of the parts or to avoid high frequenzy sounds coming from the unit.

  7. vespas permalink
    October 24, 2011 10:46 am

    hmm that doesnt look very waterproof… even a small spill will find its way in and that can be quite dangerous. try getting some heatshrink film, you can find large sizes to put the whole power supply in. something like this: http://www.hobbyking.com/hobbyking/store/catalog/HXT30A.jpg

  8. October 24, 2011 1:12 pm

    Hey, that’s excellent advice. :D
    I never thought of it because my electronic stuff does not come near water.

  9. tornekov permalink
    October 24, 2011 1:19 pm

    Great job!
    I think more people should get used to fix things themselves instead of just throwing away and buying new things when it isn’t really needed!

  10. October 24, 2011 7:48 pm

    I had exactly the problem. I used electrical tape though

  11. forivall permalink
    November 3, 2011 8:35 am

    Your post got me to post about my power adapter hacking. I took a different, long term approach. http://forivall.wordpress.com/2011/11/03/my-collection-of-zombie-power-supplies/
    My laptop is 4 years old, but the only thing that’s broken is the battery, and it still has ~60% of its original capacity.

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