this houghton gear sounds alot like our johns and waygood stuff with motor control. we have fs1,fs2 etc to control the stepping out of the pattern cct which in turn are controlled via inductors going thru vanes in the shaft. i would be looking at the other controller and do a basic system watch to see the slowdown of common relays that step up and down. it should be easy to notice 3 or 4 relays that go in/out in sequence and they should be your speed relays. it also could be like others have said that a section of your resistor bank might be open cct. if your reed switches are shorted you might see these speed switches jump 2 relays at a time, while if not it could be your resistors. let us know how you go mate.
