Yaesu MH-31A8J issue

Discussion in 'Microphones, Speakers & Audio Processing' started by KF6BL, Jun 10, 2021.

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  1. KF6BL

    KF6BL Ham Member QRZ Page

    The other day I went to use my FT-857D with a new VHF antenna. Wanted to test to see if I was hitting all the repeaters I have programmed in. Keyed the mic and announced my call sign. Repeater activated and I moved on. Went down to HF Maritime Mobile Net and tried to check in and got no reply yet I can hear the Net Controller clearly and loud. I noticed when I keyed the mic and spoke, there was no movement on the ALC meter. Changed to MOD meter and same, no movement. Went back to FM, turned on the handheld to 146.52, keyed the mic, no audio out of the handheld. So I guess I have a bad mic. Ordered a new one.

    Now, I took apart the mic and disconnected the element. Test with an ohm meter and got no value, not even zero ohms. It is as if the meter leads were not connecting to the element. Does this confirm that the mic element is DOA? I read that I should at least see the impedance value, I believe for this mic element that would be 600Ω.

    Since the microphone is still in really nice condition, I don't want to discard it. I would like to replace the mic element. Does anyone have a recommendation for a replacement element? I read that the Monacor SA-18 is a good candidate. Anything else?

    Thanks in advance
    Brian D

    added - Not interested in modifying the microphone, just want to replace the bad element.
    Last edited: Jun 10, 2021
  2. N1VAU

    N1VAU XML Subscriber QRZ Page

    Yup, the mic element is dead as a door nail, meaning it's "open" no ohms.
    Had one on an FT-817 recently. Ended up with an eBay generic replacement that worked well for $26 delivered.
    I couldn't as easily found a replacement element to fix the old mic.
  3. KB0MNM

    KB0MNM Ham Member QRZ Page

    Attached Files:

  4. KF6BL

    KF6BL Ham Member QRZ Page

    Thanks for confirming that N1VAU.

    I will check out those links you sent KB0MNM. Thanks
    N1VAU likes this.
  5. W9GB

    W9GB Ham Member QRZ Page

    It is a Old Design (now about 20 years).

    Dynamic Element Yaesu MH-31A8J Technical Supplement (2003)
    MANY Modifications for the Yaesu MH-31 microphone are posted on the Internet
    (use GOOGLE or your favorite Search engine to FIND),
    including a Voice Keyer by DH8BQA (Germany) that totally replaces the Factory PC board.
    Original MH-31 Dynamic Element on LEFT; DH8BQA Voice keyer (w/Elecret element on RIGHT)
    Most frequent modifications are fitting a replacement Dynamic microphone element
    (like the Shure R96) OR changing to an Elecret microphone element.
    Wimo (Germany) sell a replacement PC board for Yaesu MH31A8J and MH31B8 microphones.
    MH-31 PCB, Reasonable price: € 5.46 without VAT, plus shipping.
    Earlier QRZ Tech Forum discussion, September 2020
    Last edited: Jun 11, 2021
  6. KF6BL

    KF6BL Ham Member QRZ Page

    Don't think I want to venture that far. Also not a contester anymore so the voice keyer would be an overkill. LOL Thanks for the info and links, W9GB.
  7. W9GB

    W9GB Ham Member QRZ Page

    There are a number of Dynamic microphone elements available.
    Your most important criteria is to measure the Diameter and Thickness of the old Yaesu MH-31 dynamic element, so that you can choose a New Element — with minimal Retrofit work.

    Electronics Surplus (Mentor, OH) routinely has Overstock or Discontinued Microphone elements from CTI Audio (former Astatic Corp. professional division) as well as the highly regarded Panasonic Elecret mic elements (Panasonic left Elecret market, a few years ago)
    Here is a 400 ohm Z element, unknown mfg.

    Electronics Surplus has a Dynamic element from Taiwan (FV272/1740)
    that is same form factor as the old Heil HC-5 element. Unknown if identical.
    Shure R96 Dynamic element was used on the Series II of the 450 and 526 models.
    Nice sounding element, about $25 on the market (Google for best price, in stock).
    Frequency Response Chart found in Figure 2
    Last edited: Jun 17, 2021

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