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Flex 6300 Hum on TX Monitor-No RF power and No Mic Connected

N2FAN2FA Member
edited August 2019 in FLEX-6000 Signature Series

I have owned a Flex 6300 for a while. I just went from Tech to Extra so I was tuning my my mic up to embark on 20M phone. I was listening via the monitor and headphone when I noticed a hum/noise in the TX monitor audio. I had the  power on 0, so no RF. I removed the MIC and the hum was still there. I moved the unit to another part of the house with a different power supply and only the power lead,headphones, and Ethernet connected. On TX the hum and noise was still there. Here is a recording I made with an Iphone.


It sounds louder in the recording then it is. I'm holding the earphone to the Iphone mic so the clicking in the beginning  is me placing the earphone up to it.When I'm talking the noise becomes more faint and it is not as noticeable.With the DEXP on it does not present itself until I talk. 

The audio TX meter pulses with no mic connected and I'm not transmitting. If I shut the 20DB preamp off the sound goes away. It almost sounds like the preamp is picking up some fan noise. 

I tried TX and listening on a RS shortwave radio and I could hear some noise when I spoke but I cannot be sure it was not the RS portable either.

I have done some research on here, but did not want to jump to conclusions until I heard from some of the experts here.


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  • Tim - W4TMETim - W4TME Administrator, FlexRadio Employee admin
    edited August 2019
    I have converted this topic to a support HelpDesk ticket (http://helpdesk.flexradio.com) for expedited issue resolution.  If anyone else is experiencing an issue similar to this one, please submit a HelpDesk support ticket for issue resolution.
  • Steve W6SDMSteve W6SDM Member ✭✭
    edited August 2015
    Congrats on your Extra, Paul.  This is the 50th year since I was first licensed and I am still having fun.

    I see that Tim opened a help desk ticket for you, which makes sense.  I listened to your recording and it sounds nothing like the usual suspects, which are bad ground, RF, or mic/speaker impedance mismatch. 

    I'm sure they will track it down.


  • N2FAN2FA Member
    edited March 2018
    Congrats on your 50th year.  I hope I can can live long enough to accomplish the same thing one day.

    Tim was quick with the initial assessment and a return label.  It may be an internal  ground line that picks up some internal noise in the radio and allows it to get into the mic input. It will be on it's way for repair tomorrow.

  • PA1ECPA1EC Member
    edited March 2018
    Hi Tim,

    I have exactly the same problem, is there a solution for this? Because this post is 3 years old? Could it be a bad grounding of the flex?

    Eric PA1EC
  • Jay NationJay Nation Member
    edited March 2018
    Without more details, I'd guess that you have an audio ground loop. Do you need some tips on preventing them? Might seem complicated, but there are simple fixes, that usually only need to be dealt with correctly once.

    Some problems get quickly self-resolved and don't receive any replies, they then hang around in the community's search history forever. Many of us have run into ground hum issues that we had to correct for. 

    73 Jay / NO5J 
  • N2FAN2FA Member
    edited March 2018
    I recall it being an a ground point issue with the mic circuit that allowed the ground line to pick up some internal noise in the radio and allowed it to get into the mic input. I don't have the part number that Flex said was replaced, but it sounded like it was a known issue that some users experienced. I can't say for sure we have the same issue but that solved it for me.
  • Bill -VA3WTBBill -VA3WTB Member ✭✭✭
    edited March 2018
    Can you try unplugging the headphones, speakers, anything you can. then try it again? so the only thing you have connected is the mic, antenna, and lan.
  • Jay NationJay Nation Member
    edited March 2018
    There was an issue like that with some of the early 6300's, but later radio's were said to have had that corrected before they were shipped. but Eric's might be one of those that were never caught. 

    73, Jay / NO5J

  • PA1ECPA1EC Member
    edited March 2018
    Mine has week 42 2014 as production date, so the early version i gues?
  • Jay NationJay Nation Member
    edited March 2018
    Flexradio knows which radios did, or didn't get the modification.
    You should probably submit a helpdesk ticket to get the service department actively assisting you. They may not see this Community thread.

    This was all discussed for several weeks here in Community threads so you might find your answers by searching, but Flexradio can probably find the answer much easier. 

    73, Jay / NO5J

  • edited August 2019
    Does anyone know what the actual fix was for this issue?

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