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Need help on Electro Voice MT2500 Wireless Microphone

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    Need help on Electro Voice MT2500 Wireless Microphone

    Recently, I got the Electro Voice MT2500 Wireless Microphone system. It consists of a receiver and a microphone.

    According to the manual, there is a transmitter mic-level control on the microphone. And we should turn it up so that the audio level meter (consist of 10 leds) with 8 leds light up. I found that I only got 1 or 2 leds light up. Also, I have to turn the volume of the amplifier higher than normal to have enough audio output from the speakers. Therefore, I tried to turn up the mic-level control but I found that it is already on the maximum level. So I think that there may be something wrong with the microphone.

    I opened up the microphone. I sprayed the mic-level control with contact cleaner but that does not change anything. I looked at the bottom of the pcb and found that it seems a smt component is missing.

    Attached please find the photos. One of them is with a red circle showing the suspected area with missing component.

    Is it really a component had fallen off or just left open? Will that affect the microphone output? What else will cause the low microphone output?
    ps: I could not find the circuit from the internet.





    Is there a component missing or just leave open?




    the red circled component is the mic-level control
    Attached Files
    Last edited by tmho; 05-14-2018, 01:27 AM.

    #2
    Re: Need help on Electro Voice MT2500 Wireless Microphone

    Can you post a better picture of that mic board, where we can see everything?
    That JRC 2043 is a dual low noise pre-amp. So depending on where these pins connect to and from that IC, it is very well possible that this missing resistor has something to do with not having enough gain.

    Comment


      #3
      Re: Need help on Electro Voice MT2500 Wireless Microphone

      Originally posted by CapLeaker View Post
      Can you post a better picture of that mic board, where we can see everything?
      That JRC 2043 is a dual low noise pre-amp. So depending on where these pins connect to and from that IC, it is very well possible that this missing resistor has something to do with not having enough gain.
      Thanks for your reply.
      Attached please find some more photos on the board.





      Attached Files

      Comment


        #4
        Re: Need help on Electro Voice MT2500 Wireless Microphone

        Are you sure the component is actually missing? it sure looks similar to the other green components in the circuit and 3572 would be its value. Could be 35.7K, measure it, they seem to be 1% resistors
        Last edited by R_J; 05-14-2018, 10:37 AM.

        Comment


          #5
          Re: Need help on Electro Voice MT2500 Wireless Microphone

          Originally posted by R_J View Post
          Are you sure the component is actually missing? it sure looks similar to the other green components in the circuit and 3572 would be its value. Could be 35.7K, measure it, they seem to be 1% resistors
          I am not sure if a component is missing there. I do not know what 3572 represents. Also, I do not find any component left in the housing which might be from that location.

          Comment


            #6
            Re: Need help on Electro Voice MT2500 Wireless Microphone

            35.7k precision resistor.
            and it's there.

            maybe you have low gain in the reciever.

            Comment


              #7
              Re: Need help on Electro Voice MT2500 Wireless Microphone

              Originally posted by stj View Post
              35.7k precision resistor.
              and it's there.

              maybe you have low gain in the reciever.
              Yes, when I look at that again, the red circle area is already with a green component with the marking of 3572. It is quite thin that made me thought that a component is missing and also thought that the marking 3572 is on the pcb.
              Last edited by tmho; 05-14-2018, 12:35 PM.

              Comment


                #8
                Re: Need help on Electro Voice MT2500 Wireless Microphone

                Originally posted by tmho View Post
                I am not sure if a component is missing there. I do not know what 3572 represents. Also, I do not find any component left in the housing which might be from that location.
                Yes, you are right. Nothing missing.

                Comment


                  #9
                  Re: Need help on Electro Voice MT2500 Wireless Microphone

                  Originally posted by R_J View Post
                  Are you sure the component is actually missing? it sure looks similar to the other green components in the circuit and 3572 would be its value. Could be 35.7K, measure it, they seem to be 1% resistors
                  Yes, you are right. Nothing missing.

                  Comment


                    #10
                    Re: Need help on Electro Voice MT2500 Wireless Microphone

                    I agree, nothing missing. Right about now and oscilloscope would come in handy to check for gain at the various stages. Do you have a second identical mic?

                    Comment


                      #11
                      Re: Need help on Electro Voice MT2500 Wireless Microphone

                      Originally posted by CapLeaker View Post
                      I agree, nothing missing. Right about now and oscilloscope would come in handy to check for gain at the various stages. Do you have a second identical mic?
                      Sorry, I do not have a second identical mic. Also, I do not have an oscilloscope. I even do not know how to use one.

                      I have a ham radio which can receive the signal from that microphone. The ham radio shows full scale signal strength no matter what the mic-level control is at. But the audio receive from the ham radio response properly to the mic-level control. Will that mean the microphone is working properly or not?
                      Last edited by tmho; 05-14-2018, 01:39 PM.

                      Comment


                        #12
                        Re: Need help on Electro Voice MT2500 Wireless Microphone

                        There are a "audio adjust" and a "squelch adjust" at the back of the back of the receiver. I have tried adjusting them and they could not help.

                        I open up the receiver. There are several "controls" for adjustment. Will there be one can help on this?
                        (I have a multimeter and know how to use it to measure voltage and current.)

                        Attached Files
                        Last edited by tmho; 05-14-2018, 02:05 PM.

                        Comment


                          #13
                          Re: Need help on Electro Voice MT2500 Wireless Microphone

                          Since this is an FM mic and receiver, the deviation and or frequency could be off on either side or even both. That would lower your "volume" as such too. Another thing that does come to my mind is if an IF gain amp is bad.

                          To check the mic properly, I'd get a hold of some tech in your radio club that has a service monitor or something that can measure the deviation of the mic rf output. If you get at least 3.5khz deviation out of it, it's fine.
                          Last edited by CapLeaker; 05-14-2018, 03:55 PM.

                          Comment


                            #14
                            Re: Need help on Electro Voice MT2500 Wireless Microphone

                            Originally posted by CapLeaker View Post
                            Since this is an FM mic and receiver, the deviation and or frequency could be off on either side or even both. That would lower your "volume" as such too. Another thing that does come to my mind is if an IF gain amp is bad.

                            To check the mic properly, I'd get a hold of some tech in your radio club that has a service monitor or something that can measure the deviation of the mic rf output. If you get at least 3.5khz deviation out of it, it's fine.
                            Thanks for your suggestion. Although I am a licensed ham operator, I did not join any radio club nor has friends with such equipment to help on that.

                            Comment


                              #15
                              Re: Need help on Electro Voice MT2500 Wireless Microphone

                              Sounds like the mic's R.F. output is ok (but could be off frequency) but the modulation is poor, could even be a bad mic. element If it is an electret mic, there should be a dc voltage on the 2 wires going to the element
                              Last edited by R_J; 05-14-2018, 05:48 PM.

                              Comment


                                #16
                                Re: Need help on Electro Voice MT2500 Wireless Microphone

                                Originally posted by tmho View Post
                                Sorry, I do not have a second identical mic. Also, I do not have an oscilloscope. I even do not know how to use one.

                                I have a ham radio which can receive the signal from that microphone. The ham radio shows full scale signal strength no matter what the mic-level control is at. But the audio receive from the ham radio response properly to the mic-level control. Will that mean the microphone is working properly or not?
                                Since you know the FM frequency, do you have any radio equipment to transmit into that receiver via a dummy load?

                                Comment


                                  #17
                                  Re: Need help on Electro Voice MT2500 Wireless Microphone

                                  Originally posted by CapLeaker View Post
                                  Since you know the FM frequency, do you have any radio equipment to transmit into that receiver via a dummy load?
                                  My radios can only receive but not transmit on that frequency which is 188.20Mhz.
                                  But I am interested to know why via a dummy load. I have thought of if I have the radio which can transmit on that frequency, I will transmit to see how many LED will turn on. If more LEDs will turn on, then I think the problem is with the microphone. If still only 1 or 2 LEDs will turn on, then the problem is with the receiver.
                                  Last edited by tmho; 05-14-2018, 07:34 PM.

                                  Comment


                                    #18
                                    Re: Need help on Electro Voice MT2500 Wireless Microphone

                                    right on. There will be sufficient RF radiated for the receiver to receive the signal if the dummy load is next to it. Also you won't overload the RF receive section and do damage. I've blown RX preamps before with an HT on 0.5W and 2 ft distance between the HT and the preamp. That's why the dummy load idea came into my mind, unless you have a propper RF ATT and I doubt that.

                                    Comment

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