Fw: [Kenwood] MC-60A RF

[Walt Breining]

----- Original Message ----- 
From: "Walt Breining" <n9wb at nltc.net>
To: "Roy Sakabu" <rsakabu at comcast.net>
Sent: Sunday, April 10, 2005 6:57 AM
Subject: Re: [Kenwood] MC-60A RF


> I see a clue here.
> (> Mike hooked directly to rig (MC-60A base bypassed) worked OK.
>
> I do not have an MC-60A but I became curious when I heard that several
> people were having problems with these mikes picking up RF when the base
was
> used.  So I downloaded the Schematic.
>
> Please note, that this diagram has the audio and shield leads (pin 1 and
7)
> on the mike itself reversed.
>
> ftp://80.162.141.166/manuals1/kenwood/MC-60A_Schematic@gt.pdf
>
>
> Unless I have been working too late again I found the following:
>
> On the microphone pin 1 is the Mike ground.  Pin 7 is the mike hot audio.
> But on the cord, the shield is connected to pin 7 and the yellow wire that
> is surrounded by the shield is connected to pin 1  On the stand, pin 1 is
> the hot audio in and out whether or not the preamp is in or out. Pin 7 is
> used as the audio and stand ground.
>
> So it there an error in just the diagram, or were some mikes wired this
way
> and maybe even incorrectly wired in the cord or base to correct for this?
> We recently ran into a problem with a Yaesu where the diagram and some of
> the radios both had incorrectly wired phone jacks
>
> If some of the mikes were actually Mis-wired this way, so the hot audio
wire
> went to pin 7 and the mike ground that attached to the mike case went to
pin
> 1,  This certainly would cause an RF problem that would be worsened when
the
> stand was used.
>
> You should check the inside of the stand and see that the stand ground
goes
> to pin 7 on the stand male and female.  Also check the cable to be sure
that
> the shield connects to pin 7 on each end.
>
> If you can get the plug apart on the mike, you can check to be sure that
the
> mike case, the mike element ground, and the transformer common wires all
> connect together electrically and connect to pin 7 on the mike.  The
> transformer common wires will be the wires that do NOT go to the Hi Low
> impedance switch.
>
> If you cannot get the plug apart from the mike, there is another way you
can
> check if you can get to the element.  Before you use an ohm meter on the
> mike note you can magnetize the transformer.  To do an ohm check on the
> mike, you must disconnect the hot mike element wire from the impedance
> switch and place the switch in 500 (Low) Pin 7 should show continuity to
> mike case ground.  Pin 1 should show continuity to the switch terminal
where
> the hot element wire was removed with the switch still in low.  There
should
> be no continuity between pins 1 or 7 or pins 1 or 2 when the cord is not
> plugged into the mike.
>
> If you are using a cord with a 6 pin plug on one end, Pin 7 on the 8 wire
> plug is connected to the center pin 6 of the 6 wire plug by the shield
wire.
>
> If you are using a cord with a 4 pin plug on one end, Pin 7 on the 8 wire
> plug is connected to pin 4 of the 4 pin plug by the shield wire.
>
>
>
>
> ----- Original Message ----- 
> From: "Roy Sakabu" <rsakabu at comcast.net>
> To: "'egon loeckel'" <egonaggie2 at juno.com>; <kenwood at mailman.qth.net>
> Sent: Saturday, April 09, 2005 10:58 AM
> Subject: RE: [Kenwood] HELP-Ken mc-60
>
>
> > My symptoms were:
> > ALC getting pegged and distortion on any reasonable mike gain setting
with
> > mike hooked up through base and radios hooked up to an antenna.  This
> > happened whether the amplifier was switched in or out (the amplifier is
> not
> > needed in SSB mode).
> >
> > Problems went away with any one of these changes:
> > -Rig hooked to dummy load
> > -Any other mike, including other base mikes with/without amplifiers in
the
> > base
> > -Mike hooked directly to rig (MC-60A base bypassed)
> >
> > I first put bypass capacitors between the up, down, PTT lines and
ground.
> > It helped, but the mike still had distortion on voice peaks.  I then put
a
> > 220 uH inductor in series with the mike audio line and that killed off
all
> > RF feedback.  Rather than doing the true scientific thing and removing
the
> > caps to see if they really helped, I simply stopped there and kept
> > everything in.  This can all be done right on the base PC board.
> > I've also heard that adding a ground strap from the ground wire to the
> metal
> > base plate could also help in some cases.
> >
> > Hope that helps,
> > 73
> > Roy
> > AD6ZU
> >
> >
> > -----Original Message-----
> > From: kenwood-bounces at mailman.qth.net
> > [mailto:kenwood-bounces at mailman.qth.net] On Behalf Of egon loeckel
> > Sent: Friday, April 08, 2005 9:59 PM
> > To: kenwood at mailman.qth.net
> > Subject: [Kenwood] HELP-Ken mc-60
> >
> > I have a mc-60 mike that goes in to distortion some times,
> > I think it may be the element.Does any one know of a good
> > element as a replacement? Or shoud I use kenwood ?
> > tnx egon n8el
>