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testing components

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ulot

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hi
i'ld like to know how to test if a capacitor is working fine
and i saw this kind of switch that 's connected to the circuit board in 4places how do you test that too for efficiency?
Lastly,
i have an mp3 player that just refused to come on some time ago
what could be the problem? i mean the most likely problem cos' it wasn't droped or misshandled in anyway
thanks
 
ulot said:
hi
i'ld like to know how to test if a capacitor is working fine
and i saw this kind of switch that 's connected to the circuit board in 4places how do you test that too for efficiency?
Lastly,

i have an mp3 player that just refused to come on some time ago
what could be the problem? i mean the most likely problem cos' it wasn't droped or misshandled in anyway
thanks



its probably a worn out switch..
 
Which kind of capacitor do you want to measure?
The capacitance measuring is not a simple thing. The method depends on the kind of it (ceramic, tantalum, electrolyte…) and the value of it. For 100pF to 100nF the easiest way is to connect it in a known LC oscillator (where the value of coil is known) and measure the output frequency. The unknown capacitance can be calculated. For lower values is not as simple. For the higher values >10uF is unusable the LC oscillator theory. Try to charge it with current generator and measure (or draw) the voltage on the capacitor pin. From the charging time and charging current you can calculate the capacitor value.
 
An analog ohmmeter is useful for checking larger caps. The needle will swing momentarily and return to zero if the cap is good. Make sure the cap does not have a charge on it or the meter could be damaged!
 
Russlk said:
An analog ohmmeter is useful for checking larger caps. The needle will swing momentarily and return to zero if the cap is good. Make sure the cap does not have a charge on it or the meter could be damaged!
I don’t understand exactly. For ex.: if I have a capacitor of 1000uF used as a bypass cap after a rectifier and it is dried up. The real capacitance can be 100uF. If you measure it using an Ohmmeter it looks like good. Is this really good?
 
With a little experience, you can tell the difference between 1000 uF and 100 uF by how fast the needle swings. Also, a cap that old and bad probably has enuf leakage that the needle won't go to zero.
 
Edmond said:
Russlk said:
An analog ohmmeter is useful for checking larger caps. The needle will swing momentarily and return to zero if the cap is good. Make sure the cap does not have a charge on it or the meter could be damaged!
I don’t understand exactly. For ex.: if I have a capacitor of 1000uF used as a bypass cap after a rectifier and it is dried up. The real capacitance can be 100uF. If you measure it using an Ohmmeter it looks like good. Is this really good?

The most common failure mode of electrolytics is high ESR (Effectice Series Resistance) - although it still tests as the correct value (1000uF or whatever) it no longer works correctly. You can buy or build ESR meters which measure this for you, and do it in-circuit as well - you test for ESR at 100KHz, as this is the frequency it's specified at in the datasheets.
 
thanks alot everyone but it seams you were all interested in the capacitor what about the other components?
the switch?
and the mp3 player in working now. i clean out a few parts but i think it's memory is bad cos' it stops functioning on pressing play.
 
ulot said:
thanks alot everyone but it seams you were all interested in the capacitor what about the other components?
the switch?
and the mp3 player in working now. i clean out a few parts but i think it's memory is bad cos' it stops functioning on pressing play.

A switch is easy to test, simply connect an ohmmeter across it, when the switch is ON the contacts read S/C, when they are OFF the contacts read O/C.
 
Test it using the RC time constant.

resistor in parallel with a cap.

You will have to remove the cap to test it right? So then RC constant is useful here.
 
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