Sprocket Slip Boards

Where the sprocket slip board sits in the drawworks

The drawworks takes power from the (DC) drilling motor through a chain & sprocket train to the drum. That train is positively engaged by design, which is exactly why trouble in it deserves its own annunciator rather than being left to a general overload: a chain drive is not supposed to slip, so evidence that it has is worth a lamp of its own. On the (Ross Hill) Model 1400 & 2400 line-ups the function is carried on a discrete board, catalogued as sprocket slip, sitting alongside the (DC) slide, power limit, generator exciter, & ground fault boards.

Two details from the parts list tell you how it is wired. It is fed from a small three phase sensing transformer — the same 600 V delta to 31 V type the power limit circuit uses, which is why the two are catalogued on one line — so its input is an electrical measurement taken off the 600 V system rather than a signal borrowed from the driller's throttle. & it drives its own lamp assembly on the panel, separate from the ground fault & power limit lamps beside it. When that lamp starts calling with the drawworks behaving normally, or stays dark through a condition that should raise it, the board & its sensing transformer are both worth checking before anything is torn into on the mechanical side.

Board level identification is the whole game here. These boards were built over a long production life across several company names, the legend screened on the laminate is what distinguishes one revision from the next, & a board that looks identical across the bench may not behave identically in the rack.