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Application Note 10

DXD Modification

Fix for Random Key Down or PTT Activated Upon Computer Bootup

Note: This mod is installed in current production units.

Background:

As shipped, the DXD allows passing to the radio a random CW key down or PTT active state created by the computer when it is first booted up. This modification will prevent this from happening.

Modification:

1. Tools needed: Small diagonal cutter (sim. to Craftsman 45660), 25W soldering pencil, thin solder wick (Radio Shack 64-2090B), and thin electronic solder.

2. Remove the DXD cover. Remove the two screws holding the rear panel to the chassis. Remove the five screws holding the printed circuit board to its mounting posts. Separate the printed circuit board/rear panel from the main chassis.

3. Locate Q3 and Q4. See Photo 1.

Q3 and Q4 Locations

4. Using a small diagonal cutter, snip all three leads of Q3 and Q4. See Photo 2.

Remove Q3 and Q4

5. Remove the remaining leads from the printed circuit board holes and clean any remaining solder from the holes using solder wick.

6. Using a small drill about 1/16 diameter, chamfer the top and bottom of the emitter pads for Q3 and Q4. Note: This action will unground the emitters.

7. Install two new 2N4401s in the Q3 and Q4 spots and solder only the collector and base leads. See Photo 3.

Q3 and Q4 emitter leads

8. Connect a jumper between the two emitters. Connect a second jumper from Q3 emitter to pin 1 of the DB25. See Photo 4.

Completed Modification

9. Reassemble the unit in reverse order from Step 2.

Total time required to do this modification will be approximately 1 hour.

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