On 7 Mrz., 21:18, "Terry Stewart" <te..._at_email.domain.hidden> wrote:
> I've been in discussion with folk on the classic computer mailing list about
> this. The feeling was it could have either been the TA7259 motor controller
> IC, the associated caps or on of the hall-effect devices in the motor
> controller IC itself.
Usually this is attributed to the hall effect sensors which get a
voltage offset.
With a good sensor, you can measure half the supply voltage at the
outputs when no magnetic field is applied. The difference between both
output terminals goes positive or negative, depending on the field
direction.
With a bad part, this signal is shifted towards the positve or
negative direction. Therefore its zero crossing is not at the point
where the controller expects it, which makes the signal unreadable.
A drive with one faulty sensor will spin when started manually,
otherwise it will do nothing or oscillate. With two broken sensor, the
motor cannot operate at all.
Up to now I did not find suitable replacements for the passive hall
sensors used in the 400k drives.