W3 HHCH mic hum repair

[SD70MAC]

I been racking my brain to fix my W3's transmit hum and I finally found a way to fix it and here it is. I raised the mic element above the board with a piece of plastic tubing and this stopped the crosstalk hum completely. The tubing is 3/8 diameter X 7/16 H with a notch. It is attached to the board with Black Silicone ,a very small amount applied with a toothpick. I put some dense foam(not pictured) in the tube and around it to deaden any noise of your hand moving on the mic. I tried using a smaller diameter tubing ,but it cut the audio into the mic. I also twisted the mic element tightly and bent the wiring toward the bottom on HHCH.

This is very common problem on the W3 Astro Spectra.

 

[cmdrwill]

The problem is the shield/housing of the mic element not contacting the - side of the element.

Same problems in humming Maxtracs.

BTDT

 

[SD70MAC]

The problem is the shield/housing of the mic element not contacting the - side of the element.

Same problems in humming Maxtracs.

BTDT

This gets the mic element away from the board all together and stops the problem.The mic element never contacted the the board anyway,but when you move the element more than 1/4 away from the board it stops the hum. I agree its a shielding problem.

 

[SD70MAC]

I have added a shield over the board that got rid of a very faint hum it had after moving the mic. It is an Electro magnetic shield. The shield alone will not work ,but both items fixed it. I have a link to the picture of the shield in place. I just checked it again with another W3 user and the hum is gone.


2012-08-28_16-19-03_552.jpg picture by railroadradionc - Photobucket

 

[SD70MAC]

Here is the Mouser Part # for sheet of the shield material. It is 0.1mm thick and about 8" x 11" before you cut it to fit.





Mouser P/N 517-AB5010S

 

[SD70MAC]

revision to mod

I was fixing another W3 and it did not have as hot of a mic as the one I have so I had to make a revision to my mod.


Cut out the mic holder that it fits in from the factory.(picture 3)

This one had a worse hum so I had to go with a copper tube instead of plastic.( It is still 3/8 X 1/2) Wrap the copper tubbing in the EM shield before you instal the tube. Put a piece wire insulation around the mic element so it does not make contact with the copper(picture 2). Twist the mic element wire as tight as possible then instal it in the tubing. Place a small piece of the EM shield over the mic element plug also.

Picture uploaded in the wrong order. The top picture is the finished product,2nd picture is the wire insulation to protect the mic element and #3 is what I cut out to help the mic gain issue.