D700 Interface Battery Elimination Modification

The D700 Keyboard Interface can be operated without a nine volt battery if certain care is used in ensuring that it does not draw too much current. The Kenwood D700 can supply up to 200 ma of current from one of the pins on its microphone jack. Only 20 - 22 ma is actually consumed by the microphone, leaving on the order of 175 ma available for the keyboard interface and the keyboard that is attached to it. The IBM PC keyboard specifies that no keyboard should consume more than 300 ma, so it is possible that you might come across a keyboard that consumes too much power. However, I have yet to find one that consumed more than about 125 ma, so it is quite likely that the keyboard that you have chosen to use will fall well short of the 175 ma limit (even taking into account the minimal power consumption of the interface itself. To be on the safe side, it is essential that you use a 175 ma (or lower - ) fast blow fuse in this circuit to protect the radio. The parts you will need to modify your interface are as follows:

1. Fuse block
2. 150 or 175 ma fuse
3. 1 foot wire

To install the modification first cut about 3 inches (8 cm) of wire and strip a quarter of an inch of insulation off each end. Connect one end to the top left corner pin of the RJ-45 connector in the corner of the PC board. Make absolutely certain that this wire does not short against any of the other pins. See photo below:

 

Note: As described in the manual, the unit will power itself off after 3 minutes. You may wish to defeat this feature if you are not running the unit on a battery. To defeat the timer feature, simply install a short piece of wire between the back two pins on the right side of the pushbutton switch.

Cut a six inch (16 cm) piece of wire, strip both ends and connect one end to the positive side where the nine volt battery connect attaches to the board (if you like, you can remove the 9 volt connector first). Solder the other ends of these wires to the fuse block. Hot glue (or glue) the fuse block to any convenient place on the case (in the middle of the battery clip is a good choice). Insert the fuse. Double check your work to make sure that as you assemble the box the added wires do not short against anything else.

A kit of parts is available from Coastal ChipWorks if you would prefer to not gather the parts yourself. It is can be purchased for $5 + $2 shipping:

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