Microphone Failed

[hpibmx]

Hi,
I’ve got an old microphone which is failing to records,
It was disconnected from the mic at first I just solder it back again, but still the same.

Can anyone please help me, if the cap should be parallel like that?
And if there is anyway to measure the mic?

Thank you

[PA0PBZ]

How did the cap get there? It looks like an electret microphone and with the cap over the 2 connections like that there will be no signal left.
Look at this:



That is how it should be connected.

[hpibmx]

I really have no idea, i just opened it and there it was, so i assumed that's how it should be right?
my knowledge is basic if you know more please help me.

I even did continues mode measurement just to clarify if the cable is good.

Thank you.
 

[PA0PBZ]

I'm very puzzled by the cap, the microphone has only 2 wires and if you put a cap like that over the 2 wires you will short out the signal.
Also keep in mind that the microphone needs a voltage to work, if you just hook it up to an amplifier it will not work, see the diagram in my previous response or search the internet for "electret microphone"

[CaptDon]

That SMD cap may only be a few 10's of picofarads.
There is no problem being across the mic to trim
frequency response at the high end. It will indeed
have to be plugged into a circuit that supplies power
through a few Kohms, like found in 99% of laptops
ever made.

[PA0PBZ]

That SMD cap may only be a few 10's of picofarads.

Yes, you could be right. It looks like an MLCC but the only logical explanation must be that it is just a few pf's.

[hpibmx]

Thank you guys for your responses, let’s say the cap is normal and soldered where it should be,

What are the other ways I can test it?
What do you think of it failing?

I replay appropriate your help.

[PA0PBZ]

We already told you a couple of times how it should be connected, what is not clear?

[Wallace Gasiewicz]

You can test the electret by hooking it up as described in the previously posted schematic, these things take maybe 5 to 9 volts There is a FET intrinsic in the package. Hook up the mic to a oscilloscope if you have one, You should  see a voice pattern.
Otherwise' plug it into your computer and make sure there is voltage to the mic coming from your computer. If it does not work with volts to the mike, and it is connected correctly, it is dead. This would be terrible, I think these things are maybe a buck. If no volts to mic, check your wires.

Usually the three pin ones are better than the two pin ones.

About the cap: These electrets have a pretty flat audio response from 20 Hz to 20 KHz, maybe someone wanted to filter out the higher freq to get a better voice response, as another person postulated. With only a few volts going to the mic it is unlikely the cap has failed. You can remove it though. Maybe there is a solder problem. You could check the cap with an ohmeter for a short just like it is now without removing it.

Wally

[hpibmx]

Thank you Wally for your explanation

[mikerj]

If you are going to hook it up as per the schematic the resistor will typically need to be in the 1k-10k range.  Check that the output is biased somewhere near the middle of the supply range, though it's not critical to get it right in the middle as the output swing is pretty small.

Did you check to make sure that cap is not shorted?  If you have no way of measuring its capacitance it may be worth temporarily removing it, it's possible a previous person has fitted a part with an unsuitably high value.

[brabus]

That cap seems damaged. Have you checked it's not shorted?

[mikerj]

I just tear it down more out of curiosity, it was nothing but a transistor I guess?! A transistor microphone combined?

Look at the schematic that PA0PBZ posted above and you will see a JFET.  An electret microphone capsule would have an unusably high output impedance by itself so they are always combined with a JFET transistor.

[floobydust]

[...] I took a picture and the number is 596B.

It's a common JFET 2SK596 special for electret mic use. They are always stuffed inside the can.