expert question about detecting bad caps

[hifihifi]

On most recent laptop motherboards, almost no electrolitic capacitors are used anymore.

They use a lot tantalium and ceramic capacitors in parallel.
This is very good to create low ESR but sometimes there are about 50 very little capacitors in parallel. Here is a picture http://www.behardware.com/medias/pho...IMG0039304.jpg


Because it is "impossible" to remove all capacitors and measure one by one and then resolder one by one, is there a way to "test" what capacitor is broken, sow I only have to replace one capacitor?

I tried with LeakSeaker 89 but without succes.

Never tried heat camera...

[dj_ricoh]

Re: expert question about detecting bad caps

i just bought a lab psu.
i`m trying to inject some voltage and see the behavour;
still learning

[hifihifi]

Re: expert question about detecting bad caps

Respect max voltages, these chips cannot handle many voltage, max cpu voltage is around 1V.

[mariushm]

Re: expert question about detecting bad caps

Those capacitors under the cpu are usually within 0.01uF - 0.1uF - 1uF, they're decoupling capacitors.

They're ceramic, probably 10v rated max... and it's so high simply because of voltage bias in ceramic capacitors or to put it in some simpler words with ceramic capacitors the actual capacitance goes down as you get close to the capacitor's maximum voltage rating... a 1uF 10v capacitor will have 1uF at 1-2v but may have only 0.5uF at 7-9v)
Less often you'll find some larger ceramic capacitors (0805 or higher) which will generally be 4.7uf-10uF 50v or something like that

The larger surface mount capacitors, usually the ones that also have a line drawn on them (for polarity) are tantalum capacitors. Those are generally used for their higher capacity (10-47uF) and because they aren't affected by the circuit voltage as ceramics are affected.
Also, above around 10uF, ceramic capacitors are hard to make, expensive, and due to the large number of layers such large ceramics tend to get microphonic effects or break down from vibrations, flexing of board etc.

Tantalums are however more expensive than normal ceramic capacitors and they're used less often because they have a tendency to burst in flames or explode violently when damaged.

Both tantalum capacitors and ceramic capacitors have very low ESR. At least with ceramic capacitors as far as I know there's no mechanism through which a ceramic capacitor would get higher ESR.

Like I said above tantalum capacitor tend to fail short so you can measure continuity if the tantalum didn't burst in flames already. Some tantalum capacitors nowadays have an integrated fuse which breaks when tantalum shorts, so you may also see full open circuit when trying to measure continuity on that tantalum, but you won't read a capacitance with the meter.

Ceramic capacitors tend to fail open or become intermittent due to layers separating, ceramic chip cracking, poor solder joints etc. Not really much you can do to check such capacitors except doing continuity checks, measuring capacitance (but with one leg desoldered from mb), doing measurements while heating the board etc

[hifihifi]

Re: expert question about detecting bad caps

Great info.