Reading capacitance on SM capacitor

[nospam_needed]

Hi,

I'm looking at a laptop (Toshiba Sat 3000, to be specific) motherboard
that having some SMD suspecting leaky capacitors; Some basic questions
if someone can bring me up-to-date to the world of surface mount device,
that would be nice:

* There are four of them in parallel; ohm reading both way, in circuit,
about 50 Ohm. They are around the power charging area, and the circuit
having a blown fuse. Would this sound like a strong posibilty for leaky
cap ? (I can take them out one by one for sure...)

* The capacitors are the good size ones in the SMD world (6mmx4mmx3mm);
There is + sign printed on one end, and the printed note say "220" on
first line and "g14" the next line. Would that be 220 pF ? Seem little
for that size...

Thanks for any advice.

Cheers,

 

[J. Clarke]

Hi,

I'm looking at a laptop (Toshiba Sat 3000, to be specific) motherboard
that having some SMD suspecting leaky capacitors; Some basic questions
if someone can bring me up-to-date to the world of surface mount device,
that would be nice:

* There are four of them in parallel; ohm reading both way, in circuit,
about 50 Ohm. They are around the power charging area, and the circuit
having a blown fuse. Would this sound like a strong posibilty for leaky
cap ? (I can take them out one by one for sure...)

* The capacitors are the good size ones in the SMD world (6mmx4mmx3mm);
There is + sign printed on one end, and the printed note say "220" on
first line and "g14" the next line. Would that be 220 pF ? Seem little
for that size...

220 pf is the best bet. If they are showing 50 ohm both directions then
either they're completely dead or you're measuring resistance through some
other part of the circuit--for a capacitor you should be seeing a low
initial resistance that increases over time as the capacitor charges.

 

[mike]

nospam_needed wrote:




220 pf is the best bet. If they are showing 50 ohm both directions then
either they're completely dead or you're measuring resistance through some
other part of the circuit--for a capacitor you should be seeing a low
initial resistance that increases over time as the capacitor charges.

They probalby exist, but I've never seen a 220pF cap with a polarity
marking. For their size, I'd bet on 220uF.
I wouldn't count on your resistance measurement meaning bad caps.

mike

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[Frank346]

Hi,

I'm looking at a laptop (Toshiba Sat 3000, to be specific) motherboard
that having some SMD suspecting leaky capacitors; Some basic questions
if someone can bring me up-to-date to the world of surface mount device,
that would be nice:

* There are four of them in parallel; ohm reading both way, in circuit,
about 50 Ohm. They are around the power charging area, and the circuit
having a blown fuse. Would this sound like a strong posibilty for leaky
cap ? (I can take them out one by one for sure...)

* The capacitors are the good size ones in the SMD world (6mmx4mmx3mm);
There is + sign printed on one end, and the printed note say "220" on
first line and "g14" the next line. Would that be 220 pF ? Seem little
for that size...

Thanks for any advice.

Cheers,

Those are 220 uF, probably tantalum. The ordinary failure mode is a short
circuit in which case you would read much less than 50 Ohms. Some other part
of the circuit is responsible for the 50 Ohm reading.

 

[nospam_needed]

Those are 220 uF, probably tantalum. The ordinary failure mode is a short
circuit in which case you would read much less than 50 Ohms. Some other part
of the circuit is responsible for the 50 Ohm reading.

I tend to think that's 220uF as well, but all the references I've read
so far on-line indicate that the number refer to pico Fara, with the
last digit indicate the number of zero's to follow... That would make
this 22 pF, which is against any other indicators (polarity sign is not
popular for small cap, physical size of the cap...) Unless I'm still
missing other way to read capacitor from a specific manufaturer.

I know measuring resistance in circuit is not conclusive; but before
taking the cap out, I need the replacement ready just in case, therefore
I need to read the capacitance value ...

Any other hint ? Thanks for the opinion so far.