RK05 alignment - without alignment pack?

I don;t know what manuals you have, I am working from a printset (only). I find it much easier in the end to start from the schematics (which are probably the most accurate representation of the actual device). I've found too many erorrs and unclear statements in circuit descriptions (not just DEC!) over the years... No, 3 sensors. SIN, COS, LIMIT. There are 6 wires, hut the 'L' side of each sensor is earthed (check the chassis wiring diagram and the backplane wirelist in the printset). The 'H' side of the 3 sensors go to the servo analogue/preamp PCB I think you're getting confused by DECs (confusing, I'll agree) terminology. The limit switch -- the microswitch on the positioner -- produces the HOME L signal (it also, as I thought, disconnectes the emergency-retract battery). The HOME L signal is used as part of the spin-up enable circuit (I think it won't try to start a drive if the heads aren't home), and also to disable the servo REV signal on a normal retract. The OUTER LIMIT signal comes from the servo analogue/preamp board, and is derrived from the LIMIT optical sensor. Not a switch. I suspect that is the problem. Those 3 signals are critical to the operation of the positioner. Look at the G938 schematics in the printset. E14 is the the servo summing amplifier, it drives the power amplifer (on a separate PCB), otuput on pin BU2. It can take a velocity signal from E12 (for seeks) and a position signal from E6 (derrived from the SIN POSITION signal, aka SIN H) for holding on track. Also on that schematic see how the COUNT PULSE FWD and COUNT PULSE REV signals are produced (they are the track crossing signals to drive the current cylinder counter) and the OUTER LIMIT L and INNER LIMIT L signal. My experience (with anything, not just RK05s) says that if you have a problem, correct it. The drive (in this case) can't possibly work if the outputs from the optical transducer are incorrect. Disable the servo drive(put the switch on the power amplifer PCB down) and look at TP2 (pin AM1), TP4 (AS1) and TP10 (AJ1) while moving the carriage by hand (disk loaded and spinning, or you'll ruin the heads!) Next trap for the unwary. The 2 15V regulators (+ve and -ve) are _indentical_./ The mains transformer hs 2 secondary windings, both feeding bridge rectiifers and smoothing capacitors. One provides the +ve voltages (+5V, +15V), the -ve side of that bridge is logic ground. The other supplies a 15V regulator unit, and the +ve output of the regulator is connected to ground. The result is that the -ve side of the bridge/capacitor (and the common point of the regulator) is at -15V wrt ground. It's a swtiching regulator of course. What seems to have failed? -tony