I have a Hyster B60ZAC, serial number is B230N04001J with a Iskra controller in it, that will chatter when you first take off, then will smooth out after you get going. I've replaced the encoder, due to channel issues, then the motor itself along with the drive unit. With no change. I do not see any wiring issues and connections appear to be good at all connectors. I have run it with the brake assembly off of the unit with no change, it still chatters. I also tried a different tiller card. I have been unable to find the correct schematic for it. Any help would be greatly appreciated.