The microphone inside the radio is an electret. The membrane to which I believe you
are referring too is a formed rubber dampener. The microphone is about 0.25 inch
in diameter and a cylinder about 0.25 inches high. Printed circuit board vibrations
on which the electret microphone is mounted are dampened by a rubber sheath
placed over the microphone. That sheath also has a lip that folds over and under
the microphone to mechanically isolate it from the printed circuit board. The gap
formed under the microphone by the rollover of the sheath is critical and the sheath
is in place when the microphone is soldered to the board.
The opening in the sheath for audio does little to alter the bass audio frequencies.
Rather I suspect the electret microphone simply is out of spec.? The diagram below
displays the covering cloth on a typical CUI design electret microphone. Notice they
show a 'non-woven fabric layer'. Also notice that is all that stands in the way of dust,
dirt, debris and spit encroaching on the inside of your microphone. You can remove
it, but you are inviting Murphy to throw a party down the road.
As the old label on radios and telephones use to say, "There are no internal
consumer serviceable parts". The pictorial below shows the assembled micro-
phone stack up. You can see why the fabric layer is critical to leave alone.
In all probability if your reports indicate poor audio, the microphone audio
response was bad from the beginning or debris and/or moisture has ingressed
the microphone. The fix is to replace the microphone. Last time I purchased
an electret from Icom (not Yaesu but Icom for an Icom repair) the microphone
was $1.35 and the shipping was $11.50. So call Yaesu and ask for the replacement
microphone. Alternatively if you can indentify the manufacturer's label and
model number on the 'make you squint your eyes to read' printing on the
microphone case you may find it listed in Mouser, Digikey, or other distributors
catalog. I buy direct from the radio manufacturer when possible and also
purchase the rubber dampener at the same time. Being rubber they do break
down and nothing is more aggravating than trying to find a glue that does not
stick you to yourself while trying to coax the torn rubber of the dampener to
stick together.
Please do not use a Weller soldering gun or a soldering iron rated more than
30 watts to desolder the microphone. Do use 'Desoldering Wick' such as
Chemtronics or similar desoldering braid. A substitute is a scrap of coax braid
dipped in liquid flux intended for electronic use. Make sure to determine what
solvent is needed to clean the flux. Many modern fluxes are intended to be
cleaned in a water/saponfier solution and will resist cleaning with many
differing alcohols. If the flux cleans with alcohol buy a box of 'Alcohol Swabs'
like used to clean the skin before a hypodermic injection. You can buy a box
at the pharmacy or Sam's Club in the home medical supplies aisle for less than
about $2.50. Clean the board three or four times with the swabs if used. Don't
use toilet paper soaked in alcohol or paper towel soaked in alcohol. Been
there, done that and cussed for three hours while using tweezers under a
stereo zoom microscope picking out paper fibers that caught misc sharp
points on the tracks and protruding leads.
Displayed below is the typical electret microphone frequency response.
The audio circuitry in the FT-60 will add some pre-emphasis so the flat
curve of the microphone will be altered to produce a positive slope. The
audio chain schematic is shown below if you would like to observe the
audio passband processing used in the FT-60R. If the microphone is
not the problem than there is likely an issue with one of the audio
gain stages that amplifies and filters the microphone audio. My money
is on the microphone.
Regards
Chuck WD4HXG
Nick N6VOA
Chris Smart
Clint Bradford