Find out that the problem is not with the stepper motor. I checked two of its windings, the resistance of both is 22 ohms. oiled the spindle but did not give any results. the motors are controlled by two Darlington assemblies of the STA434A transistor. they are very hot over 50-60 degrees Celsius. I watched the signals with an oscilloscope on these assemblies of transformers, at one output of a constant voltage of 12 volts, and at the other output a high-frequency signal of more than 1 MHz and an amplitude of 12 volts is generated. It looks like self-excitation, due to the breakdown of the trasistor. if I move the head from the initial position with my hands (it is mandatory with rotating discs), then when I turn it on again, the head returns to its initial position. assuming Darlington transistors are punctured. I'm currently looking for where to buy them.