needing some help on the reason why the direction contactors trip twice as soon as the start switch is closed or creep speed then trips open. if I hold the forward direction contactor or reverse contactor in manually while I have someone operate the controls ithe traction motors runs fine bbut *** soon as I let go it trips back to open. I have replaced the following with new parts and have not solved it. new scr1 scr2 scr5 direction contactors, control card,ix transformer. voltage is good at control panel. what am I missing