Jay B. calls. Pete Francis, et al. have gone looking for signals that might be present on various corrector coils even when the FFB (fast feedback) or beam modulation systems are off... the goal being to try to find the source of the y-position double-peaking.
They have verified that when the FFB system is off, the relevant coils have no current sent to them. Good.
However, they find that even with the beam modulation off, the modulation coils apparently receive a 240 Hz square wave with something like a 75 mV amplitude, which seems to come from the LEMS current transducers (which come after the Trim cards, but before the coils themselves). Somehow these transducers can apparently create a signal, not just measure one (shades of Heisenberg....).
So, as a test, they have powered off the box in which these LEMS current transducers sit (and, I believe, they have checked that the coils no longer see any signal).
We should leave these off, at least for this evening, so we can run some beam and look to see if the y-double-peaking is there or not.