I've been using the same dual stage controller for 4 years....(knocking on wood)
They seem to be pretty hit or miss. Not sure about repairing them, what is the problem you are experiencing with it? Also, did you wire it yourself, or did it come wired?
I have 4 of them, 2 of which I've had for ~5 years. bought them prewired.
sorry to hear your bad luck man.
the people at ranco seem pretty responsive, and I know of one case where they flat out replaced a friend's unit at no cost, no questions asked. give their website a try.