HI there
An Update

Thanks to the information sent through, we managed to work out the feed for this contactor called the balance contactor comes from the unit, but for some reason does not alway send the feed. We stripped the sevcon sc2000 and soldered the base pcb along with some connections on the card. The circuit components appear ok from the checks we can do but the problem still persists. Sometimes the balance contactor comes in immediately othertimes after a few seconds or few minutes...can anyone suggest if there is a method of getting round this problem. (customers site engineer tried bridging contactor out, but still will not work unless contactor energises)