Disk detection on the Persci 270 series drives (and I think on the 299 series drives as well) is simply a microswitch triggered by the leading edge of the diskette. There are NO electronics in the insert detection / clamp / eject mechanism. It is a trivial circuit consisting ONLY of a DC electric motor (24 volts, I think) and 4 microswitches (two of these are operated by cams on the motor shaft, one is the front panel eject switch and one is triggered by the diskette itself when it's pushed in). All you need to troubleshoot it is a multimeter. It has no connection to the actual "electronics" of the drive. It's just straight DC electricity. Schematics are available on the Harte site and in other places if you don't have the manuals. The only thing different about the CS3 implementation is that they removed the front bezel of the drives, and then replaced the eject switches that had been part of the drive's own front bezel (now removed) with a switch on the CS3 chassis. I don't remember if they connected this through the switch wires left over from the (removed) Persci front bezel or if they did eject through the 50-pin data interface connector (Persci did allow an eject function through the 50-pin data cable).