the heads (more precisely the tape path) rarely go out of alignment. more likely they are dirty- leave a 3hr tape running overnight and see if the pic returns: failing that, clean them with a piece of chamois leather and alcohol from the chemists .see www.repairfaq.org for a guide on how to do it safely
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cassette recorders.