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mettula

caps

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Hi mettula

Test for open circuit (which a capacitor should be) using high Ohms range, there may be an initial 'kick' of the meter display but it should become infinity.

Test for short circuit, anything lower than infinity Ohms indicates leakage and the worst case being a short circuit (0 Ohms).

Test for good: One way is to connect a battery or power supply to the capacitor via a high value resistor and at the same time measure the voltage across the capacitor.  From a knowledge of the supply voltage and resistance of the resistor you can make a reasonably accurate guess at the capacitors value using the voltage rise time formula for a capacitor.

Hope that helps

Ed

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what i really mean is how to know which capacitor is faulty if it is in a circuit. For example - I
have an amplifier and it has its'left channel - no sound is coming out - the coupling cap is off and how to locate it.
Also when no input signal the sub makes a 100Hz noise is it the decoupling cap?if yes how to locate it

thanks for your patience

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Hi mettula!

A shematic is always a great help and amplifiers with two equal channels is also a great help when you are into fault finding cause you can compare the signals by following it's way through the two channels.
100hz in your sub amp sounds like a bad filtering or that something have happend with your input stage, measure for dc at the output of the amp there should be no more than tens of mV, there could be a few decoupling and filter caps in your amp so where they are is not that simple to say unless you have schematic to upload.
If you have a scope it is much easier to check for open capacitors in the way of the signal but another way of doing it is as EdwardM mentioned in his post.
What brand is it and do you have any schematic?

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the brand is labtec and has also written with 3D spatilizer 3Ds sound.as for version on the main board there is written labtec BG main REV 1.5. it uses a pait of tda2005 as amplifiers, also present there are 2 LM386, 2 TL074, LM13600 and PSZ740P :-[ :-[ :-[

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It is rare for a capacitor to short. They usually "open".
Are you sure the problem is a cap?
The best way to find out where the sound stops in an amp is to introduce a tone into the input of the amplifier and follow the signal through the circuit until it stops. This could be done with a tone generator and scope or a signal injector / receiver circuit.

MP

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