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

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Hi,

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.

https://app.box.com/s/cs50f1g301hzmxsz5annp13kbgopukyb

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.

Thanks 
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N2FA

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Posted 3 years ago

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Tim - W4TME, Customer Experience Manager

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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.
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PA1EC

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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?

73,
Eric PA1EC
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Jay / NO5J

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Eric 
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 
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N2FA

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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.
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Jay / NO5J

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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. 
 
#Flexradio

73, Jay / NO5J

(Edited)
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PA1EC

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Mine has week 42 2014 as production date, so the early version i gues?
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Jay / NO5J

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PA1EC
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. 
 
#Flexradio

73, Jay / NO5J

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Steve W6SDM

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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.

73,

Steve
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N2FA

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Steve,
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.

73's
Paul
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Bill -VA3WTB

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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.