Icom IC-740
Electronic Keyer (IC-EX243) Modification
The original keyer has a small flaw. When it is powered on it sets the key down momentarily. By design this happens whenever you switch to CW mode. When you switch any other mode the power (8V) is disconnected from the board. This is actually a behaviour of the chip Curtis 8044 as described in 8044print.pdf.
To prevent this unexpected keying I made the following modification, see mainly the schematics diagram.