Zoom the screen with Alt+Scroll in KDE
Install xbindkeys, qdbus.
Enable KWin zoom effect. For best experience, lower the zoom multiplier.
Add this to .xbindkeysrc in your home folder (or create the file):
It is possible that
qdbus is available under a different name, like
qdbus-qt4. Try the command itself (without quotes) and see if it has any effect.
You may want a different modifier. For Meta/Super key, replace
m:0x50 + c:133.
killall xbindkeys xbindkeys
xbindkeys to startup.