Testing SMD caps

[sam67]

When testing SMD capacitors on pcb using 200 ohm setting does it give reliable readings when testing for shorts and opens ?

Just thought i'd ask ,what other methods do you use ?..i do have mike's Esr v4 for the electrolytic caps.

[999999999]

Re: Testing SMD caps

No. Some circuits will have parallel paths, though if you had a reading of totally open you can be sure the cap isn't shorted at that particular moment.

[sam67]

Re: Testing SMD caps

Thanks for your reply ,what is the best method that can give a reliable reading when using either digital or analogue meter.

[shadow]

Re: Testing SMD caps

In reality, to test nearly all components reliably requires you to remove the component from the circuit. Test it and either put it back in circuit if it is alright or replace it if it has failed.

[sam67]

Re: Testing SMD caps

In reality, to test nearly all components reliably requires you to remove the component from the circuit. Test it and either put it back in circuit if it is alright or replace it if it has failed.

Trouble is there are loads of smd caps on a main board and to remove them one at a time would take forever.. surly there must be an easier way

[999999999]

Re: Testing SMD caps

Do you really need to test all the SMD caps? I'm sure there are some SMD 'lytics on mainboards somewhere, but generally most, the rest aren't very prone to failure unless the solder joints crack from flexing the board too much.

What you can do is check for the expected values in each subcircuit when power is applied. A multimeter will do that for some circuits, or a scope for the rest. If circuit meets needed parameters the caps can be assumed sufficient/ok/good enough/etc.

[stj]

Re: Testing SMD caps

SMD leak like government.

put a soldering iron on the "-" pin and see if it stinks - that's the first test.

[sam67]

Re: Testing SMD caps

Hi guys ,

Thanks for the response ..I just wanted to get more info on testing smds like caps resistors e.t.c in case i come across a problem in the future ..Just looking for a quick way of confirming which are bad and which are good so i can eliminate them.

The SMD components are that small and trying to desolder them one at a time would be a real pain just to see which ones had gone bad.

[stj]

Re: Testing SMD caps

they leak far more often than they fail "in secret" if you know what i mean.

[999999999]

Re: Testing SMD caps

sam67, be more specific. Testing a circuit is all about exactly what the circuit does. There is no one way to test "a mainboard" because it is comprised of so many circuits.

Generally speaking the only way to have a clear and sure determination that a capacitor is good, within specs, is to desolder it. Yes it would be a real pain but if you are speaking of the non-electrolytic capacitors there is not any real reason to suspect them at all unless you have a specific reason and in that case, you would replace any that are suspect.

A suspect part would have visual abnormality, or if you just suspect a cracked solder joint you can reflow that joint. If you measure a short you have to pull all parts in the subcircuit till you find it. If you measure too much ripple, only then suspect a drift in capacitance value or open circuit at capacitor(s).

Generally speaking though, we have a paradox. Electrolytic capacitors are among the most likely discrete components to fail in switching power supply subcircuits, but non-electrolytic surface mount capacitors are among the least likely parts to fail in subcircuits so the better thing to wonder is what else in that subcircuit is the first place to look.

[sam67]

Re: Testing SMD caps

Thanks 999999999 ,

I was just curious about the small SMD components but your answer ,

Well, answered that for me

Cheers

sam67