add a key-binding in emacs init file:
(global-set-key (kbd "C-:") 'avy-goto-char)
for avy-goto-char function.
When I press down Ctrl and :(with Shift pressed), nothing happens. But when use Meta-x avy-goto-char, the commands list window shows C-: already bound to this function. And this function works well.
And if I replace char : to j (for example), it works fine. Anyone met this problem before. Please help