G2 is the screen grid voltage, the AKB is to do with regulating beam current and image brightness and helps limit the set for x-ray protection. The two are very much linked in that the higher the screen grid voltage the the higher the beam current, causing AKB to regulate other voltages and make sure the beam current doesn't get too high.
Unless i have this totally wrong, and AKB is like the black level balance. This is related to the timing of the back porch following the sync interval and preceding a new burst/line, and would actually have more to do with the vertical sync pulse not being caught, now i think about it. If this is the case, i don't think it will be flyback-related.
None of which helps you in particular, sorry! Just telling you to have a look at the vertical sync section is pretty vague, but so is telling you to look at voltages.