Nagra III - Page 19

Page 16
Motor spindle. The motor spindle turns in a ball race indise the motor and
on a bearing holder und erneath on the end plate. It can happen that a film
of lubricating oil and, on the bearing holder, a l ayer of aluminium oxide
which protects the bearing holder and the chassis from corrosion, becomes
sufficiently insulating so that the spindle is no longer effectively earthed.
In this case the parasitic in the motor find another route to earth. The
parasitics so passin g may in truth be extremely small but it is possible
that this may happen. This trouble can be diagnosed when it is found that
the noise disappears, then the spindle is earthed by touching the capstan
with a wire to earth. In general, it is sufficient to eliminate these
parasitics by carefully earthing the end bearing holder and removing
the oxide on the seat of the screw holding the bearing holder, but in a
very bad case a little metallic brush on the back of the capstan is
obviously the most certain method.