[ICOM] RE: HM-56a Very Low Audio

[Hsu, Aaron (NBC Universal)]

Hi Mark,

I remember my IC-2410's mic also had low audio.  The solution I was given was to remove the clamping diode that's across the mic leads.  Sorry, don't remember exactly where that diode is located anymore, but it's near the mic element - might even have been on the mic element itself. 

OK, just found this via Google:

http://www.wb4hfn.com/Modifications/SM6140

Specifically about fixing low-audio with the HM-56/A

Also found references to leaky caps on the HM-56 circuit board that causes a stuck TX condition.  Here's a link to a PDF of the Icom service bulletin.  Shows the location and values of all the caps affected.

http://www.radagast.org/~dplatt/hamradio/hm-56_electrolytic_replacement.pdf


If you have problems with either of these links, Google "icom hm-56" (without the quotes) and you should be able to find lots of info.

73,

  - Aaron Hsu, NN6O


-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On Behalf Of butwheat
Sent: Thursday, March 13, 2008 11:15 AM
To: icom at mailman.qth.net
Subject: [ICOM] HM-56a Very Low Audio

Howdee,

Anyone run into this and find the cure? The TT pad fully modulates the
radio, but talk audio is waaaaaay down. Do condenser microphones go weak?
The battery measures O.K. (albeit under no load).

adTHANKSvance,

Mark
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