Amstrad 3in disc drive troubleshooting

Well, if th sell has 2 piles of similar devices (in the case I mentioned, IDE hard drives), it's very hard to avoid assuming that 'untested' realy means 'not working'... I haev no problem with 'sold as seen' or 'not working' or whatever. And I do rememebr that in most cases I am buying something that's 30 years old or more, so I don't expect it to look and work like it's just left the factory. Howeever, it should not have parts missing (particularly not complete PCBs or subassemblies) unless I am told about it before I buy it. For example, some years ago I bought a non-working HP9820 calcualtor on E-bay., Indeed it wasn't working, but it was complete (the fault turned out to be a 7495 chip on the memroy address PCB). I was therefore happy with my purchase. Had there been PCBs missing, while the description would still I suppose have been correct, I would have been unhappy. I learnt years ago that having a reasoanble hand tool kit upstairs (screwdrivers, torx drivers, pliers, etc) saved a lot of going up and down stairs to fetch tools for minor repairs, or to check I'd pulled the right machine out of the spare bedroom :-) Good idea. Even if the coercivity is differnet, the signals will look much the same, just different amplitudes. The one exception to that might be the Sony single-sided full-height 3.5" drive, which has a step-up transfoemr between the head and the read amplifier, apparently the head signal amplitude was too low otherwsie. But you'd recognise that it you saw it. I wonder if you you use parts from the Amstrad 3" drive, and bits from other drives to make soemthign that works. As I said, the read circuit in the ASIC of the Amstrad drive looks awfully like an MC3740 from the external components... -tony