docs or software for Quay 900 (uses Quay 90F/MPS board)

Based on a fairly limited amount of testing, it does seem that the data separator circuitry in the Quay 900 might be inadequate for reliable double density operation. My formatter program does a verify pass after formatting, and disks formatted in single density on either drive read back consistently, but double density with an 0xe5 fill byte gets a few read errors on the inner (higher-numbered) tracks on drive 1, and many read errors on the inner tracks on drive 0. I've tried writing other data patterns after formatting, such as 00, 11, aa, 6db6db, 924924, and pseudo-random data, and some of those patterns cause noticably higher read error rates, though I haven't yet collected enough data to draw any conclusions about specific patterns. I also don't know how much write precompensation the Quay is doing, nor whether they enable precomp based on TG43. I suppose it's possible that the electronics of the drive is not performing as well as it should. Unfortunately the CDC/MPI manual on Bitsavers doesn't cover the specific variant of drive in the Quay. It has a PWA that is noticeably different than the ones covered by the manual, with fewer ICs and more potentiometers. Without matching documentation I'm not about to start tweaking pots, though it's entirely possible that their values have drifted to suboptimal settings. I'm considering tracing out the schematic of the FDC to drive interface enough to hack in an SMC FDC9216B data separator.