Hi Dave,
See comments interspersed.
On Fri,1/16/2015 7:47 AM, Dave Hachadorian wrote:
The microphone in my Yamaha CM500 Headset has failed. DC measurements
at the plug show:
tip and ring shorted
That's normal -- it's wired that way, I think, for compatibility with a
wide range of computer stuff.
1270 ohms tip to shell with negative ohmmeter lead on shell
810 ohms tip to shell with positive ohmmeter lead on shell
The output of the mic is a FET-follower that gets the very high Z of the
mic element to an impedance that can drive our circuits. That bias is
applied through R on the order of 5K to the tip, and the 5K resistor
serves as the load. As I recall, Elecraft is using 5.6K. So the FET is
what you're reading with the Ohmmeter.
The above measurements lead me to believe that the problem is not at
the connector end, but rather in the element. I'd like to take a crack
at repairing the unit. Mouser has a wide selection of electret
elements, starting at $0.58.
I've been using CM500s for nearly 5 years now. I've had two with broken
cables, both of which I have retired and replaced with a new CM500.
Any ideas as to how would I go about disassembling the mic enclosure,
and can someone recommend a specific electret element?
Electret capsules are pretty generic, so almost anything would likely
work if it fits. No ideas about getting it apart. However -- is it
possible that the bias circuit or connector adapter has failed?
I really like the CM500 for radio, but the difficulty of repair is a
negative. The way I look at it is that I can buy several of these for
the cost of other stuff that is less comfortable and doesn't sound as
good. :)
73, Jim K9YC
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