Icom IC-740

Marker Unit
(inspired by Icom IC-EX241)

It is almost impossible to get this optional module todays. I decided to make my own one.
The original Icom module is controlled by a simple 3.2 MHz crystal (in HC49/U). The below module is controlled by 12.8 MHz VC-TCXO.
The function is quite identical as the original one but it is more stable.

The sinus signal from VC-TCXO is converted to TTL levels by a Schmitt trigger, then divided by 74HC4040 ripple counter, then switched by 74LS00.

The bottom view of the unit.

The unit mounted at its standard position on the RF BOARD.

Schematics diagram

PCB layout (top view):

Green: bottom cuprum
Blue: non-isolated wires under the ICs. They must be placed before ICs are soldered. They are mounted on the top side of PCB.

Mind the three parts mounted on the bottom side. There are two SMD condensers there and one 1N4148 diode. The diode is soldered between pins 4 and 11 of the 74LS00.

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