I have dissablembled 4 broken seagate HDD, retired the logic board and cover top, I noticed that not all HDD are the same model because not all have the same number of plates inside, I thought that all 4 disk would be the same model because all looks identilcal and none have its external labels.
Whatever looking the related circuitry of the VCM the coil connections are exposed to pins used to connect to logic board, so I use a multimeter and search for a low resistante value.
On these pins I have 10 Ohms value, I applied 5V and the actuator arm moved fast, reversed the polatrity and the actuator arm move to opposite direction, the same test on the other 3 HDD revealed that despite they are different models all use the same two pins and read 10 Ohms value.
Starting from here I think that a operating voltage of 4.5 to 5 Vcd for each VCM is good enough for this experiment.
Is needed to remove a little piece of metal near the VCM, is used to maintain the actuator arm on rest position when is not in use, this because it doesn't allow a free movement of the HDD arm because when the arm is on certain position the magnets atract it to rest position.
Using pliers I carefully remove the metal post...
Now the HDD actuator arm can move freely on his restricted range.