Hello, a question for people with detailed knowledge of the 550EX's internals. I just realized the manual mode (M) on my old 550EX does not work - no matter what flash power I set, the flash always fires on full power (on a 5D, G6, and an old fully manual Yashica SLR). The flash works perfectly well in ETTL (except perhaps at very short distances where it tends to overexpose, but maybe that's a design limitation). Any ideas what is wrong and which part (or circuit board) needs to be checked and/or changed? I have already fixed two minor problems with the flash and am fairly confident with taking it apart, changing parts, and putting it back together. I'd rather do it myself than go through the hassle of getting it to the Canon service center and having to pay a fat flat fee for the repair. Thanks in advance for all suggestions.