[ICOM] Mic problem on IC-756-ProIII

[Bill Wehling]

Jim-
If you have no voltage on pin 1 as Ken mentioned, then it is likely a blown 
RF choke. These are connected in series to various lines on the back of the 
microphone jack.  They may also be mounted on a small circuit board, 
depending on the model of your radio.  It is strongly recommended you 
replace it with another choke, if blown.  This is designed to keep RF 
feedback out of the radio.

Bill Wehling
Amateur radio N5VE
----- Original Message ----- 
From: "George Waschka" <awaschka at bellsouth.net>
To: "ICOM Reflector" <icom at mailman.qth.net>
Sent: Wednesday, June 26, 2019 12:24 PM
Subject: Re: [ICOM] Mic problem on IC-756-ProIII


>I don???t know about the 756 series but one of my other Icoms had a low value 
>resistor in line, I suspect as a fuse. It was blown, perhaps due to some 
>accessory that shorted the pin to ground.
>
> Al, K5TAN
>
> Sent from my iPhone
>
>> On Jun 26, 2019, at 12:09 PM, Ken Winterling <wa2lbi at gmail.com> wrote:
>>
>> Jim,
>>
>> There may be a loss of the DC voltage that coexists with mic audio on Pin 
>> 1
>> of the mic jack.  Check that Pin 1 of the mic jack has approximately 
>> +8VDC.
>> as measured to Pin 7.  The Icom electret mics require that voltage for
>> operation.  The Heil mics, I believe, are dynamic and do not use the
>> voltage. They have a DC blocking cap.
>>
>> Ken
>> WA2LBI
>>
>>
>>
>>
>>
>>> On Wed, Jun 26, 2019 at 11:35 AM JimR <KD1YV at oneyv.org> wrote:
>>>
>>> After being in non-climate-controlled winter storage and a 500 mile
>>> move, I put my 756-III in service.  I tried the stock mic, an HM-36, but
>>> have no RF power, and no indication on the ALC meter. I swap in my Heil
>>> pro headset, and the mic in that works fine.
>>>
>>> So I figure my HM-36 did not survive the cold.  I call HRO to order a
>>> replacement, but they tell me it is discontinued, and offer me an HM-219
>>> which I buy.  I plug that in, but it has the exact same symptoms.  No
>>> RF, no ALC.  Again the Heil headset mic works fine.
>>>
>>> As an aside, I plug in my SM-30 mic, and it has the same symptoms, but
>>> it has been a bit flaky for a long time, so I can't say that is a valid
>>> test.
>>>
>>> Has anybody already solved this problem?  Thanks!
>>>
>>> --
>>> 73 de Jim, KD1YV
>>>
>>> -
>> ----
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>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
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>
> ----
> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/
> To support QSL/QTH.net: http://www.qsl.net/donate.html