I have a wired Shimano Flightdeck SC6502. The head set battery failed and when I replaced it the display showed only Km/h which is the initial screen for setting data. I followed the manual instructions for entering data but neither the B or A switches had any effect. I ultimately gave up and ordered a new head set from Amazon. Not much better. I hit the AC switch and get to Km/h. I have been able to get that changed to mph using the A switch and set it using the B switch. After that the problems begin. Sometimes the A switch works to change setting, sometimes it doesn't. Sometimes the B switch works to lock in a setting, sometimes it doesn't. Sometimes that data I am expecting shows up, sometimes it doesn't.

Does anyone know of any tricks to get these switches to actually perform the job they are supposed to perform?