There is a jumper inside the Alinco DX-77T to provide +8v bias on the 
microphone audio + line.  If you enable this Jumper you can use 
Electret microphones with out having to build a separate voltage 
insertion circuit.

JP1 is just to the rear of VR14 the Microphone Gain control on the PC 
board.  You can find JP1 on the schematic (which came with the radio) 
Just above VR14, and just left of TP1. The bias circuit consists of 
R338, R339 and C281 all of which are already present on the board.  
Actual bias voltage will be less than 8v depending on the load 
presented by your microphone.

I used a magnifying glass, and a sharp grounded soldering iron to 
bridge the solder pads JP1. Be sure to open up the original hand MIC 
and install a capacitor in the audio line to avoid having DC running 
through the coil of the dynamic microphone.

       KA9CAR
       John Dewey
       
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I have also seen a mod to change the radio's band plan.  One jumper 
sets US Bands,  One sets Japanese bands.  Both set EPROM bands  and 
NONE sets the radio unrestricted.  I saw this information in a 
copyrighted book, and once on a news group. I have no need to go out of 
band, so I did not note the details.  I suspect this would upset the 
radio's "band scan" feature, which causes it to scan with in a 
specified amateur band.
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