If you are trying to get it to work in an A650, you will have to make the SD card bootable.. it is in the CHDK wiki about how to do this. You will need a card reader of course to do this. Once it the card formatted and made bootable, copy the diskboot.bin to the card, then LOCK the card with the little switch. place the card in the camera, turn it on, and CHDK will load:D NO PS.fir file is needed.