Microphone Failed - Page 1
Forum section: electronics / repair

author: hpibmx
author_rank: Regular Contributor
timestamp: June 03, 2020, 01:49:27 pm
content: 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

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 03, 2020, 02:39:06 pm
content: 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.

author: hpibmx
author_rank: Regular Contributor
timestamp: June 03, 2020, 02:55:00 pm
content: 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.

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 03, 2020, 03:15:48 pm
content: 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"

author: CaptDon
author_rank: Super Contributor
timestamp: June 03, 2020, 03:33:02 pm
content: That SMD cap may only be a few 10's of picofarads.There is no problem being across the mic to trimfrequency response at the high end. It will indeedhave to be plugged into a circuit that supplies powerthrough a few Kohms, like found in 99% of laptopsever made.

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 03, 2020, 03:36:37 pm
content: Quote from: CaptDon on June 03, 2020, 03:33:02 pmYes, you could be right. It looks like an MLCC but the only logical explanation must be that it is just a few pf's.

author: hpibmx
author_rank: Regular Contributor
timestamp: June 03, 2020, 04:09:32 pm
content: 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.

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 03, 2020, 06:28:01 pm
content: We already told you a couple of times how it should be connected, what is not clear?

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: June 03, 2020, 10:02:46 pm
content: 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

author: hpibmx
author_rank: Regular Contributor
timestamp: June 04, 2020, 07:29:57 am
content: Thank you Wally for your explanation

author: mikerj
author_rank: Super Contributor
timestamp: June 04, 2020, 08:17:52 am
content: 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.

author: brabus
author_rank: Frequent Contributor
timestamp: June 04, 2020, 08:53:43 am
content: That cap seems damaged. Have you checked it's not shorted?

author: mikerj
author_rank: Super Contributor
timestamp: June 07, 2020, 05:17:38 pm
content: Quote from: hpibmx on June 04, 2020, 02:57:59 pmLook 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.

author: floobydust
author_rank: Super Contributor
timestamp: June 07, 2020, 11:40:36 pm
content: Quote from: hpibmx on June 04, 2020, 02:57:59 pmIt's a common JFET2SK596special for electret mic use. They are always stuffed inside the can.