Need help on a project and possible article

Michael Chisena ka2zev at
Wed Dec 9 08:47:33 CST 2009

There has been some issues with Icom DTMF microphones.
Worked on two of them so far.
The symptoms seem to be 'hang up' in transmit and flaky audio.
What I found on the first one was weak SMT electrolytic caps.

As some of you know I have an ESR meter. 
It measures the 'equivalent series resistance' of a cap.
A good cap measures less than .5 ohm. 
The ones in the Icom Mics were in the 5 to 15 ohm range. 
As a percentage it's huge.
Anyhow, I fixed the first one by removing the failed electrolytic caps. Replaced one 100uF with a new part and the two 10uF's with SMT monolithic caps.
So far it has not failed since.
Got a second Icom microphone from a client on the West Virginia border.
It too had bad caps, but the 'hang up' in ptt was caused mostly by gunk in the switch it's self. 
Cleaned and lubricated the switch, and it's been working fine since.
What I would like to do is 'borrow' a couple of failed or weak Icom DTMF mics and see if my 'fix' works on more than two examples.
I would be willing to do this repair at no charge and 'loan' out a 2m radio for the duration so that you have something to talk on.
Share a thought.
Mike Chisena
ka2zev at

"You are, what you do, when it counts" 
The Masso

"Gravity, the quickest way down" 
Mayor John Almafi

"You ever drop an egg, and on the floor you see it break? 

You go and get a mop so you can clean up your mistake. 

But did you ever stop to ponder why we know it's true? 

If you drop a broken egg you will not get an egg that's new?" 

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