IC02AT.5

ICOM HS-10SAVOX MODIFICATION
The ICOM headset VOX model HS-10SA for the IC-O2AT can be a
handy unit for mobile use but it has a serious limitation as
it comes from the box.  There is no way to turn it off other
than unplugging it!  This means any conversation with a
passenger, cough or sneeze goes out over the air.
Fortunately there is any easy remedy.  Remove the 3 screws
holding on the rear cover and the single screw holding the
circuit board.  Carefully lift out the board and locate R23.
It is a 4.7K 1/8 W resistor located near the lower edge of
the board.
One end of it connects to the white lead of the cable to the
HT.  The other end connects to the collector of Q7.  This is
the keying circuit.  In normal operation, Q7 is saturated
when the VOX is active.  Since the emitter of Q7 is grounded,
R23 is effectively connected from the white lead to ground,
keying the HT.  Carefully unsolder the end of R23 which goes
to Q7 and lift this lead out.
Drill a 1/4 inch hole in the center of the end of the case
and mount a SPDT switch.  The switch the author used was a C
& K 7207 which is a 3 position, center off, SPDT, with one
side spring return momentary and the other side latching.
This allows the momentary side to be used to key the HT
manually, the latching side for the VOX operation, and the
center OFF.
Now connect the center pole of the switch to the end of R23
which used to go to Q7.  Connect the latching side of the
switch to the hole in the board where R23 was (Q7) and the
momentary side of the switch to ground (shield of cable to
HT).  Now reassemble the unit and test.
                        RELAYED  BY...N0KGX...GENE