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KB2LJJ Radio Mods Database
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Alinco DX-77T
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
**********
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.
http://www.kb2ljj.com/data/alinco/dx-77t.htm20/08/2009 18.30.25