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How can I easily find damaged SMD capacitors without removing them from the PCB? I want to repair my laptop's graphics card (ATI Mobility Radeon x300). I have done a visual inspection of the board and I couldn't find any damaged parts on it. I think it might be a capacitor problem. I tried using a digital multimeter to find damaged components but did not find any. Whenever I take my damaged computer parts to the repair shop, the repair guy easily finds the faulty part with the same multimeter that I have and repairs it in less than 15 minutes but they charge a large fee so I am trying to do it by myself. I am new to SMDs.

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  • \$\begingroup\$ There isn't anything different about SMD capacitors that would be detected with a multimeter vs. through-hole ones. Could you find it for through-hole? \$\endgroup\$ – Brian Carlton Jun 14 '12 at 22:11
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    \$\begingroup\$ The one time I had a problem with a graphics card, the capacitor(s) that were faulty were little electrolytics that had literally blown their tops off (they are scored with an X on the top just to allow this to happen safely). So you might want to inspect those first. \$\endgroup\$ – tcrosley Jun 14 '12 at 22:20
  • \$\begingroup\$ @BrianCarlton - There is no hole on the bord, because it is SMD.Are you talking about this en.wikipedia.org/wiki/Through-hole_technology ? \$\endgroup\$ – Farid-ur-Rahman Jun 14 '12 at 22:20
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    \$\begingroup\$ There are plenty of electrolytic capacitors in SMT packages, so that wasn't clear from the question. \$\endgroup\$ – tcrosley Jun 14 '12 at 22:23
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    \$\begingroup\$ Those can look like multimeters, but they are actually impedance analyzers. People use them as ESR meters for caps. Good ones cost a lot. \$\endgroup\$ – user924 Jun 14 '12 at 23:20
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Detecting ceramic SMD capacitors with a multimeter is going to be very difficult, basically impossible in a practical sense. Forgettaboutit.

Capacitors look like opens at DC, which is what multimeters measure. You can try inspecting every one with a jeweler's loupe and looking for cracks in the caps and their solder joints, but the chances of seeing even a truly cracked cap are small.

Ceramic caps aren't the likely suspects when the board fails. Electrolytic caps are much more likely to fail, and some of the failure modes are visually obvious. You say you only have SMD caps and later say they are not electrolytic, but I am not convinced you understand that SMD and electrolytic are orthogonal and how to spot a SMD electrolytic. Look for anything that is roughly cylindrical and check if the top is really flat. As tcrosley said, the larger electrolytic caps have scoring in the metal at the top so that they fail in a controlled way if they rupture, and are less likely to take other parts with them. Replace anything that looks bulged, it doesn't need to be outright ruptured.

Still, the chance of finding a fault on something as complicated with sophisticated construction as a modern graphics card by using a meter and visual inspection is slim. Unless you value your time at pennies/hour, you'd be better off just getting a new graphics card.

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Ultra-simple Integrator & Differentiator for in-circuit capacitor testing:

The following but should be usable in many cases.
Cost (apart from the oscilloscope :-) ) is a few cents - but you will probably have the parts already available.

Equipment:

  • Oscilloscope
    Square wave generator
    Resistor
    Signal Probe
    Ground probe.

Remove all power from target board.
Float target board (no power connections etc.)
Conmnect target board to ground with ESD strap or 10 megohm resistor from true ground to target ground .

Feed signal via resistor to Oscilloscope.
Common scope ground with signal source ground. A square wave will be seen on scope.

Place probe ground on one end of capacitor and signal probe
Capacitor will affect signal and you will get characteristic rounded edges square wave.
This is a classic integrator.

Value of cap and resistor will affect result.

enter image description here enter image description here

Diagrams from here


If there is lots of loading on the PCB the above response may be excessively "swamped" to be useful.

Equipment:

  • As above but no resistor.
    Extra lead to feed signal to Capacitor "input"

"Ground" connection is other end of any device etc that may be loading cap down.

Apply signal source directly to one side of capacitor. Apply ground to other side of any load on other side of cap. Observe with scope at other side away from signal generator.

Thusly:

Capacitor shown characteristic "spike" with exponential delay. This is a classic differentiator.

enter image description here

Again, frequency, and capacitor and load values will affect result.

Diagram from here
Site reference is here but it would not load properly for me.

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All caps including SMD's can be measured the same way with a cap meter or and an ESR meter. Just don't be intimidated by the size and shape of the SMD because they all still can be measured the same.

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    \$\begingroup\$ He did say the capacitor is in-circuit. \$\endgroup\$ – stevenvh Aug 14 '12 at 16:04
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Appling 100V peak is a sure way to guarantee you will need a new board. Most capacitance meters use a voltage source less than the turn to on voltage of the IC in the circuit. This allows the measurement of the cap not be hidden by the IC's. Once you have determined that some caps are bad, (because you have a schematic diagram), you don't know which ones because they are all in parallel, you can start unsoldering them one at time until you find the bad ones, you know, like finding the bad bulbs in Christmas tree lights. Save your money and buy a new board.

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