Wednesday, 12 September 2012

Fixing my broken laptop

Last  Saturday saw a huge tropospheric lift on VHF and UHF. The amateur bands were apparently buzzing with activity and scanner enthusiasts were reporting lots of new signals. Unfortunately I wasn't at home so missed most of the action.

However I did manage to have a Sunday to tinker to my hearts content, I will post up some details of what I got up to when I have more time. I did get an excellent capture of the ISS downlink for the ARISS school contact and did some experiments with receiving some UHF Satcom stuff.

One thing I finally got around to doing was removing the motherboard from a sick laptop. It is a HP/Compaq laptop and suddenly died one evening. It would no longer boot and flashing a diagnostic code on one of the LEDs. The code was "GENERAL SYSTEM BOARD FAILURE". The laptop is quite nice and was going to form a key component of the shack and so I was determined to repair it if necessary.

I did some googling and it seems the model in question is prone to failure of the GPU, or more specifically failure of  the contacts between the GPU and motherboardl. This is a common fault now in many devices especially those with components that run hot (Xbox/PS3 etc)

It is thought that the temperature and thermal stresses involved cause one or more of the contacts to break. On inspection of the heat sink over the GPU and CPU I was shocked at the poor mounting and application of thermal pads/paste which undoubtedly made the problem worse.

The suspected faulty GPU is mounted using a ball grid array, where the contacts are under the component the problem with this is you cannot easily repair or replace the contact without specialist equipment. What is required is to reflow the solder joints, heating up the component sufficient so the solder underneath melts reforming the contact.

Several methods of 'homebrew' repair are available using heat guns, blow lamps or placing the board in a hot oven but due to the delicate nature of the board and risk to surrounding components aren't recommended.

As luck would have it I had access to a Infra-red rework station, this device has a high intensity infra-red lamp which heats the component and a heat pad underneath to pre-heat the circuit board. The advantage of this is there is no risk of movement to the components during the process and the temperature can be accurately controlled.

Well I had a go, and can report the motherboard is now working or at least now boots up. I just now have to replace the thermal bonding under the heat sink to hopefully prevent it happening again and then the small matter of putting it all back together!

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