RD54 Stopped Spinning

Thanks for that, it is something I have been looking for for some time. Page 9 of that .pdf seems to show the spindle motor controller. My guess is the 3 signals H1, H2, H3 are the signals from the 3 hall sensors in the motor. I think I would start by seeing what is there (look as though they should be TTL signals, so easy to check) and also see what the Z8 is sending to the motor driver circuits. Y1 is the clock crystal, see page 12 of that pdf. I assume it is oscillating, do you see the expected 6MHz on pin 9 of U41? I don't think it'll be possible (or at least not at all easy to replace the hall sensors. My guess is that the angular position of the platters is critical and they won't centralise accurately enough either. So I would only dismantle the HDA as a (very) last resort. -tony