Hofmann Snap-on Y2k Service Manual Download

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At reaching the pre-set speed, torque is cut back. The low torque is set to a rate, compensating
the friction, for the most part, caused by the belt and by air drag of the wheel.
Torque reduction is accomplished by lowering the voltage supplied to the motor with an AC
controller, located on the Power Interface board. Utilising semiconductor devices, this novel
AC controller provides arc-less switching for a long service life.
Unbalance measurement is carried out with reduced torque at slightly in- or decreasing speed
of the main shaft, hence avoiding pendulum oscillations in the motor.
Measurement speed can be held within set bounds to any length of time by varying the motor
torque. Detecting the speed via the incremental encoder B8, speed control is implemented in
software by varying the pulse-duty factor to the AC controller. Subsequently, the already
reduced voltage supplied to the motor is varied by 5% (dual-mode control).
With more than 150 RPM of main shaft speed, the torque capacitor C

is switched off by

relay K4 under program control. With increasing speed, the effect of C

on torque drops and

reactive current increases.
Direction of rotation of the main shaft is appointed by the order of wires attached to connector
X42. Connect motor wire marked 2 to the left-hand terminal 1, wire 3 to terminal 2 and wire 3
to terminal 3, the red/green wire to the right-hand terminal 4 of connector X42.
ATTENTION! There were IGBT failures within the drive system on the Power Interface
board.
To improve reliability,

remove the Surge Arrester F8 from Power Interface board.

CAUTION! There are two Surge Arresters on the Power Interface board. Do not remove the
one with the red coloured body!
The Power Interface board equipped the four black heat sinks; the Surge Arrester is located
between the heat sinks and the relays beside a 2k Ohm 2 Watt resistor.
The more recent Power Interface with one heat sink, the Surge Arrester marked F8 is located
in front of the heat sink.
The Surge Arrester F8 has a cylindrical white ceramic body with red printing on it, metal
discs on both ends with wires welded to in the middle of the discs.

Belt tension

With the Y2K drive system, belt tension is crucial as it has great influence on friction.
Friction can hinder extended measurement runs, e.g. service code C63. If friction uses up
more energy than supplied to the motor during prolonged measurement, the speed will drop
and measurement will be terminated. During a normal balancing cycle (10 revolutions) with a
wheel clamped on, the effect of friction will hardly be noticed. Before the speed reduction
becomes significant, unbalance data collection is completed and the brake is turned on.
Excess belt tension puts extra load on the ball bearings and can reduce measurement accuracy.
With the belt too slack, it will slip causing premature wear and in most cases, disturbing
squeaking noises as well.

Exchanging the belt and adjusting belt tension

Tools required: open-end wrench 13-mm width across flats, big screwdriver,

¼" ratchet with hexagon socket wrench 10-mm width across flats.

Four hexagon distance bolts are fastened to the shield of the electric motor, in order to obtain
room for the Multirib belt between motor and its support bracket, welded to the vibratory
tube.
To exchange the belt, the motor together with the distance bolts has to be taken off from the
bracket.
For the three upper spacer bolts, curved oblong holes are punched in the bracket. The lower
bolt serves as a swivel pin for the motor.
To adjust the belt tension, slacken the four screws (10 and 13 mm across flats, since two are

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