This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
Reference: FAQs Resource file R006SPDKNOB.GIF Adding a Speed Control Knob to your Disk ][ Drive This article tells how to move speed adjustment from the Disk ]['s dark interior to a handy front-panel location and how to "tune" the drive for optimal performance. One drive-test software vendor states that Disk ][ is good for about 500 hours of normal use between speed adjustments-- not exactly a strong argument for placing the control on the front panel! On the other hand many of today's Disk ][ owners are interested in applications which go beyond "normal use". Some utilities (e.g. DiversiCopy II) report rotational speed during ongoing applications; so, relocating the speed adjuster to the front panel is especially helpful. Similarly, users who want to back up their old, copy- protected wares know that ready access to speed control is essential. Finally, there is no question that, whatever your applications, periodic speed trimming will be required. When it is, you'll be very glad your Disk ] [ has a front panel Speed Knob! Adding Speed Knob To install Speed Knob you will need a good quality, linear taper 5k Ohm potentiometer, some wires, and a knob with a pointer mark or some other way to show position (e.g. a ring of numbers). Most of the work, really, consists of opening the drive and drilling a hole. There is no need to disconnect the drive from the controller card. 1. Remove the 4 bottom bolts and slip off the case. Unscrew the 4 bottom bolts holding the drive to the case bottom, and unplug the main ribbon cable. The drive can now be moved to your work area. 2. Drill a hole properly sized and centered for mounting your 5k Ohm pot in the upper right front panel. 3. Place the drive on its face and unscrew the 2 bolts which hold the small daughter board to the drive. (Be ready to catch loose spacers, washers, etc..) 4. Turn the small board over to the bottom side. Locate and cut the traces going to the mini-pot speed adjuster as shown in pic R006SPDKNOB.GIF. 5. Cut three wires, White, Gray, Black, long enough to reach from the board to the front panel. Connect these to your 5k Ohm pot and to the small circuit board as shown in pic R006SPDKNOB.GIF. (In case you cannot view the pic, what you're doing is substituting the new pot for the mini-pot. ) 6. Re-mount the daughter board. Mount the 5k Ohm pot. Install knob. 7. Bring the drive back to the computer. Slide it onto the case bottom plate, reconnect main ribbon cable, replace bottom bolts, slide on and re-fasten case top. You can use Copy II Plus, XPS, APEX, or one of several other utilities to set speed (see next question). A good starting adjustment will be near the center of Speed Knob's range. Once speed is adjusted, you can loosen and re-set the knob so that its position indicates a "correct" speed setting. ----------------------------