After years of CHDK use on my A540, the print/alt button does not give me the alt screen. With several dozen attempts, I did have a couple of successes.
There are a couple of things that might be happening here. There could be a mechanical problem with the button, there could be a problem with the way you are pressing the button, or there might be CHDK configuration issue.
First of all, you need to press and release the Print button fairly quickly to enter <ALT>
mode. If you press and hold then you get the original Canon Print functionality.
Secondly, it's possible to reconfigure CHDK for the A540 so that the DISP button acts as the <ALT>
button. Again, a short press goes to <ALT>
and a longer press changes the display mode. The option is in the CHDK Settings
menu - down near the bottom where it says <ALT> Mode Button
. This should help out if your Print button has become flakey / defective.