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Thread: microair 760 low volume

  1. #1

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    microair 760 low volume

    I have a microair 760 radio that I bought used. the volume level is so low I cant hear it when flying. I tried 3 different headsets, Zulu, Bose and soft com all with the same results.
    with plane not running it sounds great and has good transmission quality. I adjusted side tone to the max and no change.
    I'm wondering if anyone has any suggestions on what to check or if someone's had a similar issue.
    Thanks in advance, Aurele

  2. #2
    wireweinie's Avatar
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    More info please. What is the complete model number? I.e. M760- L, M, N, P, etc. Which particular volume level is to low? Receive volume (listening to radio traffic)? Side tone volume (listening to your own voice while transmitting)? Intercom volume (what you hear during intercom operation)? Do you have this radio hooked up to a stand alone intercom or is it using the internal intercom? Was this radio installed with new wires or was it 'adapted' to existing wiring?

    A couple of points; All the headsets you listed are stereo and this is a mono only radio. so are the headsets set up for mono operation? Also, the side tone pot only adjusts side tone volume, so it will only change the volume of your own voice while transmitting.

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  3. #3

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    Hello
    model #760 VHF am transceiver
    Serial# M760 005878
    Manufacturers code N10408
    it came with the connector DB15 with wires soldered to it. I soldered on extensions and have the pilot and copilot head phones conected to pin 14. Nothing is connected to speaker pin 15.
    i don't have it wired to a intercom. I have the internal intercom switched but have not tried it yet.
    it is the receiver volume that is to low. Sounds good when plane is not running but not enough volume when flying for me to hear what's being said. I've traced wires and think all is good. Towere said it sounds good on transmit. I hooked my icon handheld to antenna lead and handheld worked great with normal volume.
    i was thinking of ordering a new connector and redoing the wiring to see if I made a mistake when connecting it. But then was wondering if something in the radio could have failed resulting in lowered receiver volume.
    thanks for your interest in my problem. Aurele

  4. #4
    wireweinie's Avatar
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    Quote Originally Posted by A BELLAND View Post
    Hello
    model #760 VHF am transceiver
    Serial# M760 005878
    Manufacturers code N10408
    it came with the connector DB15 with wires soldered to it. I soldered on extensions and have the pilot and copilot head phones conected to pin 14. Nothing is connected to speaker pin 15.
    i don't have it wired to a intercom. I have the internal intercom switched but have not tried it yet.
    it is the receiver volume that is to low. Sounds good when plane is not running but not enough volume when flying for me to hear what's being said. I've traced wires and think all is good. Towere said it sounds good on transmit. I hooked my icon handheld to antenna lead and handheld worked great with normal volume.
    i was thinking of ordering a new connector and redoing the wiring to see if I made a mistake when connecting it. But then was wondering if something in the radio could have failed resulting in lowered receiver volume.
    thanks for your interest in my problem. Aurele
    I still need the 'letter' at the end of the M760. Early and late models differ slightly. It's on the data tag.

    To start with, find an old school David Clark headset to troubleshoot with. It needs to be mono. That means that the phone plug (the fatter one) only has one black band separating the tip from the base. Don't use it if it has two black bands as that is stereo headset and may be part of this problem. How are the jacks grounded? Are they mounted directly to a metal panel or are they mounted with isolation washers? They should be on the washers. Do you have a music jack wired into this line? What condition are the solder joints at the plug? Are they clean with no 'feelers' touching each other? How did you trace the wires from jack to plug? Visually or with an ohmmeter?

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  5. #5

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    Your fast.��
    There is no letter at the end of the Model#760, just a M in the serial #M760-005878 and a N in the manufacturers code N10408.
    The jacks are mounted without isolation washers.no music jack installed. Soldering was clean. I have removed the complete panel and traced the wires visually. I think I have a old mono headset and can remove the jacks from the panel to see if it makes a difference. Will not get to work on it again for a couple days.
    Aurele

  6. #6
    wireweinie's Avatar
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    If you remove the phone jacks from the panel, check to see if wires are soldered on both tabs or only one. If you have wires on one tab, for testing you will need to clip a ground wire from the threads on the jack to the same ground point as the radio. If you have wires on both tabs, insure that they are on the correct ones, i.e. ground wire on the tab that corresponds to the threads and the audio hi wire on the tab that corresponds to the spring contact.

    And since you have two phone jacks (pilot and co-pilot) make sure that the ground and audio high wires are not connected correctly on one jack and incorrectly on the other. Yeah. There's a story there . . .

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  7. #7
    wireweinie's Avatar
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    Just for info on M760's:

    Top line on data tag = base model number 'M760 AM Transceiver'
    Second line = 'Part No: M760-01' followed by a series of letters, L, M, N, O, P, Q, R
    Bottom line = 'SERIAL NUMBER 12345'

    One of the letters on the second line will be marked. That letter is the specific version. There are a couple of wiring changes and a bunch of programing changes between the early and later versions. Visually, the earlier versions have smaller knobs, on the faceplate, than the later ones do.

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  8. #8

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    Thank you for all the help.
    I have ground wires from radio ground pin to each jack. Need to verify both jacks are wired to correct jack connections. Do know both jacks work and low volume to each jack.
    will do some checking later this week and report back. I’m thinking this is a old radio. Will take a couple pictures and post.
    Aurele

  9. #9

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    Traced all connections with a ohmmeter and all wired according to version N wiring diagram. Tryed a old mono headset and a stereo headset and can not hear a difference. Also used mono headphone jacks when doing original wiring. I have panel removed from the plane and powered up on bench and now volume level seems good. Only thing is no isolation washers were used for jacks. I have some ordered. I'm wondering if the jacks being grounded to the panel could have caused a reduction in the volume level? Thanks for all your suggestions wireweinie! Aurele

  10. #10
    wireweinie's Avatar
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    It's possible. But usually no isolation washers = lots of noise.

    When installing the iso washers, make sure the shoulder of one fits INTO the hole in the panel and the flat one goes on the opposite side of the panel. I like to put the shouldered washer on the jack threads first. Slide the jack into the hole, from the back side of the panel, and center the shoulder in the hole. On the front side of the panel, slip the flat iso washer over the threads, put the thin metal washer over it, and thread on the nut.

    For anyone that needs washers, use Switchcraft part number S1028 and S1029.

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  11. #11

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    I found the problem. One end of the shielding in the headphone circuit was grounded. At the other end there was a couple of strands of shielding that when flexed or wiggled contacted the headphone circuit. This was not visible under shrink tube. Found by wiggling wires while listening to transmissions.thank you again wireweinie for all your suggestions. Aurele
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  12. #12
    wireweinie's Avatar
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    Glad to hear you found the problem. Sometimes the simplest discrepancies are the hardest to diagnose.

    Since you have verified that ground wires are soldered to the jacks, I would recommend installing the isolation washers when you re install this radio. Should minimize any noise generated in the airframe.

    Let us know how it flight tests.

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