110. HP Computer Repair

HP Desktop computers suffer from low quality capacitors. I am confused as to why they use motherboards from manufacturers that create low quality products.

Below is the motherboard that was taken from an HP Desktop computer.

Figure 1 Marks faulty capacitors located on a HP Desktop motherboard

I have marketed the capacitors that need the most attention. They are about 1000 mkf 16V, depending on the design. If you see just one faulty area, it is better to replace all capacitors that have the same capacity as the motherboard. If you have an oscilloscope, it is possible to find out if it is actually the problem of the capacitors, and even determine which one is faulty.

I use the following method to test them out on the motherboard. Most of the 1000 mkf range capacitors are used to make a stabilized voltage. On the capacitor’s pin, which is “+”, there will be a reading which will be +1.5, +3.3 or +5V depending on what circuit is checked. The reading should be stable, with no fluctuations or problems that arise.

Figure 2 Stable voltage located on the capacitor pin “+”

Make sure to use the oscilloscopes trigger for this, move the trigger line close to the signal level and move it below and above the signal. If the signal tries to “follow” the trigger level, you can be 100 percent sure that this is the bad capacitor. When on the screen shows obscure wording, rectangles or other kind of figures, this indicates a fault with the capacitor. Simply, capacitors used in the integrator circuit sums up the signal, and makes the average voltage. I would not go into further mathematics at this point.

When you first connect the capacitor “+” pin, simply use the auto function, as well as the default settings. If the symptoms described above are found on one capacitor, the capacitor replacement will help in most cases. The same procedures I would suggest on all the capacitors are left on the board, and the capacitor appearance is changed, like a bumpy appearance, or the top changed with the color gone.

To diagnose other common faults on HP desktops, like the Power Supply Unit connecting the oscilloscope probe to the +5 or +12V rail, then the diagnostic steps are like above. Usually, it means it has also faulty capacitors. I personally do not check other voltages from the PSU as they are not on a heavy load, and have less chance to fail.

The third part involves all the usual steps that deal with the hard drive. This can be checked with HDTune or GSmartControl.

The stability check can be checked using QA+Win32, which will cost money. In my opinion, GSmartControl, Memtest, HeavyLoad and Windows installation disk are tools that work well in order to verify the repair. Windows setup has certain protection features that check the file integrity on the hard drive, this is used for if something goes wrong with the system, and it will indicate the problem with an error. What should be done after the capacitor replacement, or PSU replacement stressing the system, is called verifying the repair. I have been looking for an effective and free stress test utility that is reliable, but, unfortunately, I haven’t found one good enough, so I’m using a few of them rather than just one.

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