I think there is supposed to be a trim pot for the Silent Circuit on the Cutlass circuit card - like there was on the original Silent Circuits (the canister-shaped device on Silhouette Specials, SSS Albert Lees, and used to be on EBMMs that had the MM90 pickups) - to adjust the hum cancelling for the individual instrument.
I found a photo of the Cutlass circuit card on a Reverb.com listing for a loaded pickguard: