Yaesu ft-990 mic feedback during RX ONLY in LSB & USB MODES

Discussion in 'Microphones, Speakers & Audio Processing' started by K3RJB, Aug 31, 2021.

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  1. K3RJB

    K3RJB Ham Member QRZ Page

    Good Day

    New to me Yaesu ft-990, with stock mh-1b8 mic. radio chks out well on tx and rx.

    Except in RX ONLY [ receive ONLY ] LSB and USB MODE ONLY
    there is a loud feedback (aka hot mic. ) if I speak into the mic it's like a pa thru the rig speaker.
    Tried an external speaker. same issue.
    I checked the mic plug for shorts. clean solder joints as per schematic.
    I tried an mc--60 base mic same issue.
    I performed a gen. ent. reset..... same issue

    rig is clean. I cleaned and reseated all the boards...

    filters installed.

    Any help is appreciated....

  2. K8DO

    K8DO Ham Member QRZ Page

    Is the radio transmitting when you just speak into the mic and the vox is off?
    If so that is an issue in the vox circuit and a different discussion.

    It appears that the mic audio out is somehow getting into the receiver audio chain.

    If there is anything plugged in the accessory ports, or any port, remove it. Should be power and coax only.

    If that is OK I am leaning towards a corrupted internal plug - misplaced, wrong jack, bent pins, shorted pins. broken pins, broken wire, and on and on..
    Take it apart again and go ever every board and connection with a magnifier and strong light.
  3. K8DO

    K8DO Ham Member QRZ Page

    Any change in the 990?

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